Toto jsou nejlepší fotografie z Hubbleova teleskopu za rok 2023!

Galerie

2. 1. 2024

Týden co týden máme možnost sledovat fotografie z Hubbleova teleskopu a toto jsou ty nejlepší, které pořídil v uplynulém roce 2023.

Leaving on a jet — This spectacular image shows a region called G35.2-0.7N, which is known as a hotbed of high-mass star formation. The kind of stars that form here are so massive that they will end their lives as destructive supernovae. However, even as they form they greatly impact their surroundings. At least one B-type star — the second most massive type — lurks within the region pictured here, and a powerful protostellar jet that it is launching towards us is the source of the spectacular light show. The image was taken with the Wide Field Camera 3 (WFC3), which is mounted on the NASA/ESA Hubble Space Telescope, and the region G35.2-0.7N lies around 7200 light-years from Earth in the constellation Aquila. This beautiful picture was assembled using data that were collected primarily for very specific research purposes, as are many of the Hubble Pictures of the Week. The research conducted using these data included measuring the extent of ionisation in the jets being blasted out of the protostar buried within G35.2-0.7N. Ionisation is a process by which atoms or molecules become charged, often because they are in such a high-energy environment that they have lost some of their electrons (the tiny negatively charged particles that orbit nuclei in atoms and molecules). Protostellar jets are enormous collimated beams of matter that are ejected from protostars. Collimated simply means that the matter is ejected in parallel (column-like) streams, which in turn means that the jets do not spread out much, but extend out very far in relatively straight lines. The visual result of the ejected matter is the glorious display visible in this image. Much of the nebula is dark, with light being blocked from Hubble’s view by the rich dust clouds that produce these massive stars. Near the very centre can be seen the location of the star and the jet of material it is emitting. The small, bright orange streak there is a cavity in the dust carved out by the ferocity of the jet as it streams tow

The dancer in Dorado — This vibrant and dynamic-looking image features the spiral galaxy NGC 1566, which is sometimes informally referred to as the ‘Spanish Dancer Galaxy’. Like the subject of another recent Hubble Picture of the Week, NGC 1566 is a weakly-barred or intermediate spiral galaxy, meaning that it does not have either a clearly present or a clearly absent bar-shaped structure at its centre. The galaxy owes its nickname to the vivid and dramatic swirling lines of its spiral arms, which could evoke the shapes and colours of a dancer’s moving form. NGC 1566 lies around 60 million light-years from Earth in the constellation Dorado, and is also a member of the Dorado galaxy group. Galaxy groups are assemblages of gravitationally bound galaxies. Groups differ from galaxy clusters in size and mass: galaxy clusters may contain hundreds of galaxies, whereas groups might contain several tens of galaxies. That said, there is not a precise delineation between the definition of a galaxy group and a galaxy cluster. Some astronomers have proposed that the definitions be sharpened up, with one suggestion that galaxy aggregations with less mass than 80 trillion Suns should qualify as galaxy groups. The Dorado group has had a fluctuating membership over the past few decades, with various scientific papers changing its list of constituent galaxies. As an example of why it is so challenging for astronomers to pin down members of groups such as the Dorado group, we can imagine a photograph of an adult human and a large oak tree. We have foreknowledge of the approximate size of the person and the tree, so if we were to see a photo where the person appeared roughly the same size as the tree, then we would be able to guess that, in reality, the person was positioned much closer to the camera than the tree was, giving the false impression that they were the same size. When working out members of a galaxy group, astronomers are not necessarily equipped with the knowledge of the size of the in

Same galaxy, different filters — This luminous tangle of stars and dust is the barred spiral galaxy NGC 1385, that lies about 30 million light-years from Earth. The same galaxy was the subject of another Hubble Picture of the Week, but the two images are notably different. This more recent image has far more pinkish-red and umber shades, whereas the former image was dominated by cool blues. This chromatic variation is not just a creative choice, but also a technical one, made in order to represent the different number and type of filters used to collect the data that were used to make the respective images. It is understandable to be a bit confused as to how the same galaxy, imaged twice by the same telescope, could be represented so differently in two different images. The reason is that — like all powerful telescopes used by professional astronomers for scientific research — Hubble is equipped with a range of filters. These highly specialised components have little similarity to filters used on social media: those software-powered filters are added after the image has been taken, and cause information to be lost from the image as certain colours are exaggerated or reduced for aesthetic effect. In contrast, telescope filters are pieces of physical hardware that only allow very specific wavelengths of light to enter the telescope as the data are being collected. This does cause light to be lost, but means that astronomers can probe extremely specific parts of the electromagnetic spectrum. This is very useful for a number of reasons; for example, physical processes within certain elements emit light at very specific wavelengths, and filters can be optimised to these wavelengths. Take a look at this week's image and the earlier image of NGC 1385. What are the differences? Can you see the extra detail (due to extra filters being used) in this week’s image? [Image Description: A spiral galaxy. It has several arms that are mixed together and an overall oval shape. The centre of the galaxy glows br

The protostellar object OH 339.88-1.26, which lies 8 900 light-years from Earth in the constellation Ara, lurks in this dust-filled image from the NASA/ESA Hubble Space Telescope. Winding lanes of dark dust thread through this image, which is also studded with bright stars crowned with criss-crossing diffraction spikes. The dark vertical streak at the centre of this image hides OH 339.88-1.26, which is an astrophysical maser. A maser — which is an acronym for “microwave amplification by stimulated emission of radiation” — is essentially a laser that produces coherent light at microwave wavelengths. Such objects can occur naturally in astrophysical situations, in environments ranging from the north pole of Jupiter to star-forming regions such as the one pictured here. This image comes from a set of Hubble observations that peer into the hearts of regions where massive stars are born to constrain the nature of massive protostars and test theories of their formation. Astronomers turned to Hubble’s Wide Field Camera 3 to explore the massive protostar G339.88-1.26, which is estimated to be about 20 times the mass of the Sun and is lurking in the dusty clouds in the center of the image. The Hubble observations were supported by other state-of-the-art observatories including ALMA, the Atacama Large Millimeter/submillimeter Array. ALMA is composed of 66 moveable high-precision antennas which can be arranged over distances of up to 16 kilometres on a plateau perched high in the Chilean Andes. Further data were contributed by the Stratospheric Observatory For Infrared Astronomy (SOFIA), which is a telescope that — until recently — operated out of a converted 747 aircraft. [Image Description: The field is filled with hundreds of bright stars. They are primarily blue in colour, with scattered smaller stars visible in yellow/orange. The background is dominated by cloudy grey dust, with permeating regions of dark black and orange.] Links Pan: Stellar cradle

Exploring a Turbulent Tarantula — A snapshot of the Tarantula Nebula (also known as 30 Doradus) is the most recent Picture of the Week from the NASA/ESA Hubble Space Telescope. The Tarantula Nebula is a large star-forming region of ionised hydrogen gas that lies 161 000 light years from Earth in the Large Magellanic Cloud, and its turbulent clouds of gas and dust can be seen swirling between the region’s bright, newly-formed stars. The Tarantula Nebula is a familiar site for Hubble. It is the brightest star-forming region in our galactic neighbourhood and home to the hottest, most massive stars known. This makes it a perfect natural laboratory in which to test out theories of star formation and evolution, and a rich variety of Hubble images of this region have been released to the public in recent years. The NASA/ESA/CSA James Webb Space Telescope also recently delved into this region, revealing thousands of never-before-seen young stars. This new image combines data from two different observing proposals. The first was designed to explore the properties of the dust grains that exist in the void between stars and which make up the dark clouds winding through this image. This proposal, which astronomers named Scylla, complements another Hubble observing proposal called Ulysses and is revealing how interstellar dust interacts with starlight in a variety of environments. This image also incorporates data from an observing programme studying star formation in conditions similar to the early Universe, as well as cataloguing the stars of the Tarantula Nebula for future science with Webb. [Image description: Wispy, nebulous clouds extend from the lower-left of the image. At the top and right the dark background of space can be seen through the sparse nebula. Along the left and in the corner are many layers of brightly-coloured gas and dark, obscuring dust. A cluster of small, bright blue stars in the same corner expands out across the image. Many much smaller stars cover the background.] Links Video of

A clear view of a galaxy cluster — The massive cluster Abell 3322 is featured in this image from the NASA/ESA Hubble Space Telescope, in which the galaxy 2MASX J05101744-4519179 basks in the centre. This distant galaxy cluster is a cosmic leviathan that is highly luminous at X-ray wavelengths. Observing galaxy clusters like Abell 3322 can advance our understanding of the evolution and interactions of dark and luminous matter in galaxy clusters, and also reveals powerful gravitational ‘telescopes’ that magnify distant objects through gravitational lensing. Knowing the location of these lenses can enable future observations with both Hubble and the NASA/ESA/CSA James Webb Space Telescope. The galaxy cluster is located in the constellation Pictor, around 2.6 billion light-years from Earth. The unusual alignment of the three brightest cluster galaxies in this image (two in a close pair in the centre of the image and a third in the upper right region) suggests that A3322 is observed in the process of formation. This is because at least two smaller clusters collide along an axis defined by the locations of their individual brightest cluster galaxies. However, the diffuse super-hot gas that permeates all massive galaxy clusters (and is visible only at x-ray wavelengths) is understood to be distributed in a single, almost perfectly spherical halo. In other words, it neither exhibits an elongation that follows the three-galaxy lineup, nor does it show signs of two (or more) individual cluster cores. Discrepancies like this are of great interest for astronomers who want to explore the differences in the dynamic behaviour of gas, galaxies, dark matter, and cluster collisions. Two of Hubble’s instruments joined forces to create this image: Wide Field Camera 3 and the Advanced Camera for Surveys. Both are third-generation instruments that offer superb image quality and high sensitivity to astronomers studying a range of scientific questions. Both instruments provide images of wide areas of the night sky, b

Galactic isolation — The swirls of the galaxy IC 1776 stand in splendid isolation in this image from the NASA/ESA Hubble Space Telescope. This galaxy lies over 150 million light-years from Earth in the constellation Pisces. IC 1776 recently played host to a catastrophically violent explosion — a supernova — which was discovered in 2015 by the Lick Observatory Supernova Search, a robotic telescope which scours the night sky in search of transient phenomena such as supernovae. A network of automatic robotic telescopes are spread across the globe, operated by both professional and amateur astronomers, and, without human intervention, reveal short-lived astronomical phenomena such as wandering asteroids, gravitational microlensing, or supernovae. Hubble investigated the aftermath of the supernova SN 2015ap during two different observing programmes, both designed to comb through the debris left by supernovae explosions in order to better understand these energetic events. A variety of telescopes automatically follow up the detection of supernovae to obtain early measurements of these events’ brightnesses and spectra. Complementing these measurements with later observations which reveal the lingering energy of supernovae can shed light on the systems which gave rise to these cosmic cataclysms in the first place. [Image description: A spiral galaxy. It is irregularly-shaped and its spiral arms are difficult to distinguish. The edges are faint and the core has a pale yellow glow. It is dotted with small, wispy, blue regions where stars are forming. A few stars and small galaxies in warm colours are visible around it.]

Measure of a great galactic disc — This dream-like Picture of the Week features the galaxy known as NGC 3156. It is a lenticular galaxy, meaning that it falls somewhere between an elliptical and a spiral galaxy. It lies about 73 million light-years from Earth, in the minor equatorial constellation Sextans. Sextans is a small constellation that belongs to the Hercules family of constellations. It itself is a constellation with an astronomical theme, being named for the instrument known as the sextant. Sextants are often thought of as navigational instruments that were invented in the 18th century. However, the sextant as an astronomical tool has been around for much longer than that: Islamic scholars developed astronomical sextants many hundreds of years earlier in order to measure angles in the sky. A particularly striking example is the enormous sextant with a radius of 36 metres that was developed by Ulugh Beg of the Timurid dynasty in the fifteenth century, located in Samarkand in present-day Uzbekistan. These early sextants may have been a development of the quadrant, a measuring device proposed by Ptolemy. A sextant, as the name suggests, is shaped like one-sixth of a circle, approximately the shape of the constellation. Sextants are no longer in use in modern astronomy, having been replaced by instruments that are capable of measuring the positions of stars and astronomical objects much more accurately and precisely. NGC 3156 has been studied in many ways other than determining its precise position — from its cohort of globular clusters, to its relatively recent star formation, to the stars that are being destroyed by the supermassive black hole at its centre. [Image Description: A large lenticular galaxy. It appears to be formed of faint, grey, concentric ovals that grow progressively brighter towards the core, where there is a very bright point, and fade away at the edge. Two threads of dark red dust cross the galaxy’s disc, near the centre. The background is black and mostly empty, wit

This Hubble Picture of the Week — taken using the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys (ACS) — shows Arp 107, a celestial object that comprises a pair of galaxies in the midst of a collision. The larger galaxy (on the left of this image) is an extremely energetic galaxy of a type known as a Seyfert galaxy, which house active galactic nuclei at their cores. Seyfert galaxies are notable because, despite the immense brightness of the active core, radiation from the entire galaxy can be observed. This is evident in this image, where the spiraling whorls of the whole galaxy are readily visible. The smaller companion is connected to the larger by a seemingly tenuous ‘bridge’, composed of dust and gas. The colliding galactic duo lies about 465 million light-years from Earth. Arp 107 is included in a catalogue of 338 galaxies known as the Atlas of Peculiar Galaxies, which was compiled in 1966 by Halton Arp. It was observed by Hubble as part of an observing programme that specifically sought to fill in an observational ‘gap’, by taking limited observations of members of the Arp catalogue. Part of the intention of the observing programme was to provide the public with images of these spectacular and not-easily-defined galaxies, and it has provided a rich source for Hubble Pictures of the Week. In fact, several recent releases, including this one and this one, have made use of observations from the same observing programme. [Image Description: A pair of merging galaxies. The galaxy on the left has a single, large spiral arm curving out from the core and around to below it, with very visible glowing dust and gas. The right-hand galaxy has a bright core but only a bit of very faint material. A broad curtain of gas connects the two galaxies’ cores and hangs beneath them. A few small stars and galaxies are scattered around the black background.] Links Pan: A peculiar proceeding

What’s in a name? — This Hubble Picture of the Week includes the pithily-named galaxy SDSS J103512.07+461412.2, visible in the centre of this image as a dispersed sweep of dust and stars with a denser, brighter core. SDSS J103512.07+461412.2 is located 23 million light-years from Earth in the constellation Ursa Major. The seemingly rambling name is because this galaxy was observed as part of the Sloan Digital Sky Survey (SDSS), a massive survey that began in 2000 with the aim of observing and cataloguing vast numbers of astronomical objects. So far, it has recorded several hundred million astronomical objects. In the early days of astronomy catalogues, astronomers painstakingly recorded individual objects one by one. As an example, the Messier catalogue includes only 110 objects, identified by the astronomer Charles Messier because they were all getting in the way of his comet-hunting efforts. As the Messier catalogue is so limited, it is sufficient to simply refer to those objects as M1 to M110. In contrast, when a survey as massive in scope as the SDSS is involved, and when huge volumes of data need to be processed in an automated manner, the names assigned to objects need to be both longer, and more informative. To that end, every SDSS object has a designation that follows the format of: ‘SDSS J’, followed by the right ascension (RA), and then the declination (Dec). RA and Dec define the position of an astronomical object in the night sky. RA is analogous to longitude here on Earth, whilst the Dec corresponds to latitude. To be more exact, RA measures the longitudinal distance of an astronomical object from the point where the celestial equator (the mid-point between the north and south celestial poles) intersects with the ecliptic (the plane in which Earth orbits around the Sun). The entire night sky is then carved into 24 slices, known as ‘hours’, measured eastwards from that starting point (which is designated as zero hour). This means that the RA can be expressed in

LINER on collision course — This Picture of the Week prominently features two galaxies: NGC 3558 in the lower left, and LEDA 83465 in the upper right. Both galaxies lie roughly 450 million light years from Earth. The two galaxies are separated from one another by a distance of roughly 150 000 light years, which might sound vast, until we consider that our nearest galactic neighbour — the Andromeda galaxy — is a whopping 2.5 million light years distant from the Milky Way galaxy. In galactic terms, the two galaxies pictured here are practically on top of one another. This is because they belong to a crowded and chaotic galaxy cluster known as Abell 1185, which is packed with galaxies that are interacting with one another via gravity. These galactic interactions have sometimes led to dramatic results, such as galaxies being torn apart completely. This fate has not befallen NGC 3558, which currently retains its integrity as both an elliptical galaxy and a low-ionisation nuclear emission-line region, or LINER. In fact, it probably attained its present form by devouring smaller galaxies in the cluster — galaxies much like LEDA 83465. LINERs are a particular type of galactic nucleus or core, and are distinguished by the chemical fingerprints written into the light that they emit. As their name suggests, LINERs emit light which suggests that many of the atoms and molecules within these galactic cores have either been weakly ionised or not ionised at all. Ionisation is the process by which atoms or molecules lose or gain electrons. In galaxies, it is driven by a variety of processes — from shockwaves travelling through galaxies, to radiation from massive stars or from hot gas in accretion discs. In the case of LINERs, this means that many of the atoms and molecules within the galaxies have lost either a single electron, or have retained all their electrons. The mechanism that drives this weak ionisation in LINERs such as NGC 3558 is still debated amongst astronomers. [Image Description: Two g

‘S’ is for ‘Spiral’, ‘AB’ is for … ‘Weakly Barre — This glittering image shows the spiral galaxy IC 5332, which lies about 30 million light-years away in the constellation Sculptor, and has an almost face-on orientation to Earth. To explain what is meant by ‘face-on’, it is helpful to visualise a spiral galaxy as an (extremely) large disc. If the galaxy is oriented so that it appears circular and disc-shaped from our perspective here on Earth, then we can say that it is ‘face-on’. In contrast, if it is oriented so that it appears squashed and oval-shaped, then we would say that it is ‘edge-on’. The key thing is that the same galaxy would look extremely different from our perspective depending on whether it was face-on or edge-on as seen from Earth. Check out these previous Hubble Pictures of the Week for examples of another face-on spiral galaxy and an almost edge-on spiral galaxy. IC 5332 is designated as an SABc-type galaxy in the De Vaucouleurs system of galaxy classification. The ‘S’ is straightforward, identifying it as a spiral galaxy, which it clearly is, given the well-defined arms of bright stars and darker dust that curl outwards from the galaxy’s dense and bright core. The ‘AB’ is a little more complex. It means that the galaxy is weakly barred, which refers to the shape of the galaxy’s centre. The majority of spiral galaxies do not spiral out from a single point, but rather from an elongated bar-type structure. SAB galaxies — which are also known as intermediate spiral galaxies — do not have a clear bar-shape at their core, but also do not spiral out from a single point, instead falling somewhere in between. The lowercase ‘c’ describes how tightly wound the spiral arms are: ‘a’ would indicate very tightly wound, and ‘d’ very loosely wound. Thus, IC 5332 is quite an intermediate spiral galaxy on many fronts: weakly barred, with quite loosely wound arms, and almost completely face-on! [Image Description: A close-in view of a spiral galaxy. It is seen face-on, showi

A dynamic duo … or trio? — This striking image captures the interacting galaxy pair known as Arp-Madore 2339-661, so named because they belong to the Arp-Madore catalogue of peculiar galaxies. However, this particular peculiarity might be even odder than first meets the eye, as there are in fact three galaxies interacting here, not just two. The two clearly defined galaxies are NGC 7733 (smaller, lower right) and NGC 7734 (larger, upper left). The third galaxy is currently referred to as NGC 7733N, and can actually be spotted in this picture if you look carefully at the upper arm of NGC 7733, where there is a visually notable knot-like structure, glowing with a different colour to the arm and obscured by dark dust. This could easily pass as part of NGC 7733, but analysis of the velocities (speed, but also considering direction) involved in the galaxy shows that this knot has a considerable additional redshift, meaning that it is very likely its own entity and not part of NGC 7733. This is actually one of the many challenges that observational astronomers face: working out whether an astronomical object really is just one, or one lying in front of another as seen from Earth’s perspective! All three galaxies lie quite close to each other, roughly 500 million light-years from Earth in the constellation Tucana, and, as this image shows, they are interacting gravitationally with one another. In fact, some science literature refers to them as a ‘merging group’, meaning that they are on a course to ultimately become a single entity. [Image Description: Two spiral galaxies. Each glows brightly in the centre, where a bar stretches from side to side. The upper one is more round and its arms form two thin rings. The lower galaxy is flatter and its arms make one outer ring; a dusty knot atop its upper arm marks out a third object. Gravity is pulling gas and dust together where the galaxies come close. A number of small galaxies surround them on a black background.] Links Pan: A dynamic duo … o

When amateur astronomers point the way — This image features the spiral galaxy NGC 941, which lies about 55 million light-years from Earth. The data used for this image were collected by Hubble’s Advanced Camera for Surveys (ACS). The beautiful NGC 941 is undoubtedly the main attraction in this image; however, this hazy-looking galaxy was not the motivation for the data being collected. That distinction belongs to an astronomical event that took place in the galaxy years before: the supernova SN 2005ad. The location of this faded supernova was observed as part of a study of multiple hydrogen-rich supernovae, also known as type II supernovae, in order to better understand the environments in which certain types of supernovae take place. Whilst the study was conducted by professional astronomers, SN 2005ad itself owes its discovery to a distinguished amateur astronomer named Kōichi Itagaki, who has discovered over 170 supernovae. This might raise the question of how an amateur astronomer could spot something like a supernova event before professional astronomers — who have access to telescopes such as Hubble. The answer is in part that the detection of supernovae is a mixture of skill, facilities and luck. Most astronomical events happen over time spans that dwarf human lifetimes, but supernova explosions are extraordinarily fast, appearing very suddenly and then brightening and dimming over a period of days or weeks. Another aspect is that professional astronomers often do not spend that much time actually observing. There is a great deal of competition for time on telescopes such as Hubble, and then data from a few hours of observations might take weeks, months, or sometimes even years to process and analyse to their full potential. Amateur astronomers can spend much more time actually observing the skies, and sometimes have extremely impressive systems of telescopes, computers and software that they can put to use. So many supernovae are spotted by skilful amateurs such as Itagaki that there is act

“Late-type” galaxy? — This Hubble Picture of the Week features NGC 2814, an irregular galaxy that lies about 85 million light years from Earth. In this image, which was captured using Hubble’s Advanced Camera for Surveys (ACS), the galaxy appears to be quite isolated: visually, it looks a little like a loose stroke of bright paint across a dark background. However, looks can be deceiving. NGC 2814 actually has three close (in astronomical terms) galactic neighbours: a side-on spiral galaxy known as NGC 2820; an irregular galaxy named IC 2458; and a face-on non-barred spiral galaxy called NGC 2805. Collectively, the four galaxies make up a galaxy group known as Holmberg 124. In some literature these galaxies are referred to as a group of ‘late-type galaxies’. The terminology ‘late-type’ refers to spiral and irregular galaxies, whilst ‘early-type’ refers to elliptical galaxies. This rather confusing terminology has led to a common misconception within the astronomy community. It is still quite widely believed that Edwin Hubble inaccurately thought that elliptical galaxies were the evolutionary precursors to spiral and irregular galaxies, and that that is the reason why ellipticals are classed as ‘early-type’ and spirals and irregulars are classed as ‘late-type’. This misconception is due to the Hubble ‘tuning fork’ of galactic classification, which visually shows galaxy types proceeding from elliptical to spiral, in a sequence that could easily be interpreted as a temporal evolution. However, Hubble actually adopted the terms ‘early-type’ and ‘late-type’ from much older astronomical terminology for stellar classifications, and did not mean to state that ellipticals were literally evolutionary precursors to spiral and irregular galaxies. In fact, he explicitly said in his 1927 paper that ‘the nomenclature … [early and late] … refers to position in the sequence, and temporal connotations are made at one’s peril’. Despite Hubble himself being quite

One cluster or two? — This Hubble Picture of the Week features a massive cluster of brightly glowing galaxies, first identified as Abell 3192. Like all galaxy clusters, this one is suffused with hot gas that emits powerful X-rays, and it is enveloped in a halo of invisible dark matter. All this unseen material — not to mention the many galaxies visible in this image — comprises such a huge amount of mass that the galaxy cluster noticeably curves spacetime around it, making it into a gravitational lens. Smaller galaxies behind the cluster appear distorted into long, warped arcs around the cluster’s edges. The galaxy cluster is located in the constellation Eridanus, but the question of its distance from Earth is a more complicated one. Abell 3192 was originally documented in the 1989 update of the Abell catalogue, a catalogue of galaxy clusters that was first published in 1958. At that time, Abell 3192 was thought to comprise a single cluster of galaxies, concentrated at a single distance. However, further research revealed something surprising: the cluster’s mass seemed to be densest at two distinct points rather than one. It was subsequently shown that the original Abell cluster actually comprised two independent galaxy clusters — a foreground group around 2.3 billion light-years from Earth, and a further group at the greater distance of about 5.4 billion light-years from our planet. The more distant galaxy cluster, included in the Massive Cluster Survey as MCS J0358.8-2955, is central in this image. The two galaxy groups are thought to have masses equivalent to around 30 trillion and 120 trillion times the mass of the Sun, respectively. Both of the two largest galaxies at the centre of this image are part of MCS J0358.8-2955; the smaller galaxies you see here, however, are a mixture of the two groups within Abell 3192. [Image Description: A cluster of galaxies, concentrated around what appear to be two large elliptical galaxies. The rest of the black background is covered in

This striking image shows the densely packed globular cluster known as NGC 2210, which is situated in the Large Magellanic Cloud (LMC). The LMC lies about 157 000 light-years from Earth, and is a so-called satellite galaxy of the Milky Way, meaning that the two galaxies are gravitationally bound. Globular clusters are very stable, tightly bound clusters of thousands or even millions of stars. Their stability means that they can last a long time, and therefore globular clusters are often studied in order to investigate potentially very old stellar populations. In fact, 2017 research that made use of some of the data that were also used to build this image revealed that a sample of LMC globular clusters were incredibly close in age to some of the oldest stellar clusters found in the Milky Way’s halo. They found that NGC 2210 specifically probably clocks in at around 11.6 billion years of age. Even though this is only a couple of billion years younger than the Universe itself, it made NGC 2210 by far the youngest globular cluster in their sample. All other LMC globular clusters studied in the same work were found to be even older, with four of them over 13 billion years old. This is interesting, because it tells astronomers that the oldest globular clusters in the LMC formed contemporaneously with the oldest clusters in the Milky Way, even though the two galaxies formed independently. As well as being a source of interesting research, this old-but-relatively-young cluster is also extremely beautiful, with its highly concentrated population of stars. The night sky would look very different from the perspective of an inhabitant of a planet orbiting one of the stars in a globular cluster’s centre: the sky would appear to be stuffed full of stars, in a stellar environment that is thousands of times more crowded than our own. Links Science paper in the Monthly Notices of the Royal Astronomical Society Pan video: Cluster in the cloud [Image Description: A dense clu

All lined up — This image features an interacting galaxy system known as Arp-Madore 2105-332, that lies about 200 million light-years from Earth in the constellation Microscopium. Like other recent Hubble Pictures of the Week, this system belongs to the Arp-Madore catalogue of peculiar galaxies. The wonderful quality of this image also reveals several further galaxies, not associated with this system but fortuitously positioned in such a way that they appear to be forming a line that approaches the leftmost (in this image) component of Arp-Madore 2105-332, which is known individually as 2MASX J21080752-3314337. The rightmost galaxy, meanwhile, is known as 2MASX J21080362-3313196. These hefty names do not lend themselves to easy memorisation, but they do actually contain valuable information: they are coordinates in the right ascension and declination system used widely by astronomers to locate astronomical objects. Both the galaxies are of a type known as emission-line galaxies. This simply means that, when observed with spectrometers, the spectra of both galaxies exhibit characteristic bright peaks, known as emission lines. This is distinct from, for example, absorption-line galaxies whose spectra contain distinct gaps, known as absorption lines. Emission lines are produced when gases are very hot, and therefore have sufficient energy that the atoms and molecules are ‘excited’ and emit light. In other words, emission-line galaxies are highly energetic places, marking them out as likely hotbeds of star formation. As with many galaxy types, categorising a galaxy as an emission-line galaxy does not exclude it from having other descriptions that refer to its other properties. Arp-Madore 2105-332, for example, is also a ‘peculiar’ galaxy, reflecting the atypical shapes of its two constituent galaxies. [Image Description: A pair of interacting galaxies, one smaller than the other. Each has a bright spot at the centre and two loosely-wound spiral arms, with threads of dark dust

Sighting forbidden light — This whirling image features a bright spiral galaxy known as MCG-01-24-014, which is located about 275 million light-years from Earth. In addition to being a well-defined spiral galaxy, MCG-01-24-014 has an extremely energetic core, known as an active galactic nucleus (AGN), so it is referred to as an active galaxy. Even more specifically, it is categorised as a Type-2 Seyfert galaxy. Seyfert galaxies host one of the most common subclasses of AGN, alongside quasars. Whilst the precise categorisation of AGNs is nuanced, Seyfert galaxies tend to be relatively nearby ones where the host galaxy remains plainly detectable alongside its central AGN, while quasars are invariably very distant AGNs whose incredible luminosities outshine their host galaxies. There are further subclasses of both Seyfert galaxies and quasars. In the case of Seyfert galaxies, the predominant subcategories are Type-1 and Type-2. These are differentiated from one another by their spectra — the pattern that results when light is split into its constituent wavelengths — where the spectral lines that Type-2 Seyfert galaxies emit are particularly associated with specific so-called ‘forbidden’ emission. To understand why emitted light from a galaxy could be considered forbidden, it helps to understand why spectra exist in the first place. Spectra look the way they do because certain atoms and molecules will absorb and emit light very reliably at very specific wavelengths. The reason for this is quantum physics: electrons (the tiny particles that orbit the nuclei of atoms and molecules) can only exist at very specific energies, and therefore electrons can only lose or gain very specific amounts of energy. These very specific amounts of energy correspond to certain light wavelengths being absorbed or emitted. Forbidden emission lines, therefore, are spectral emission lines that should not exist according to certain rules of quantum physics. But quantum physics is complex, and some of the rules us

It’s all relative — This Hubble Picture of the Week features a richness of spiral galaxies: the large, prominent spiral galaxy on the right side of the image is NGC 1356; the two apparently smaller spiral galaxies flanking it are LEDA 467699 (above it) and LEDA 95415 (very close at its left) respectively; and finally, IC 1947 sits along the left side of the image. ThIs image is a really interesting example of how challenging it can be to tell whether two galaxies are actually close together, or just seem to be from our perspective here on Earth. A quick glance at this image would likely lead you to think that NGC 1356, LEDA 467699 and LEDA 95415 were all close companions, whilst IC 1947 was more remote. However, we have to remember that two-dimensional images such as this one only give an indication of angular separation: that is, how objects are spread across the sphere of the night sky. What they cannot represent is the distance objects are from Earth. For instance, whilst NGC 1356 and LEDA 95415 appear to be so close that they must surely be interacting, the former is about 550 million light-years from Earth and the latter is roughly 840 million light-years away, so there is nearly a whopping 300 million light-year separation between them. That also means that LEDA 95415 is likely nowhere near as much smaller than NGC 1356 as it appears to be. On the other hand, whilst NGC 1356 and IC 1947 seem to be separated by a relative gulf in this image, IC 1947 is only about 500 million light-years from Earth. The angular distance apparent between them in this image only works out to less than four hundred thousand light-years, so they are actually much much closer neighbours in three-dimensional space than NGC 1356 and LEDA 95415! [Image Description: A collection of galaxies. On the left side a large spiral galaxy with swirling, twisted arms is flanked by a smaller, but still detailed, spiral behind its arm on the left, and a smaller spiral above it. On the right side is a fourth, round

Portrait of a Ghostly Galactic Peacock — The lenticular galaxy NGC 6684 bathes this image from the NASA/ESA Hubble Space Telescope in a pale light. Captured with Hubble’s Advanced Camera for Surveys, this lenticular galaxy is around 44 million light-years from Earth in the constellation Pavo. Pavo — whose name is Latin for peacock — is a constellation in the southern sky and one of four constellations collectively known as the Southern Birds. Lenticular galaxies like NGC 6684 (lenticular means lens-shaped) possess a large disc but lack the prominent spiral arms of galaxies like the Andromeda Galaxy. This leaves them somewhere between elliptical galaxies and spiral galaxies, and lends these galaxies a diffuse, ghostly experience. NGC 6684 also lacks the dark dust lanes that thread through other galaxies, adding to its spectral, insubstantial appearance. The data in this image were captured during a census of the nearby Universe entitled Every Known Nearby Galaxy which aims to observe all galaxies within 10 megaparsecs (32.6 million light-years) that the telescope has not already visited. Before this programme began Hubble had observed roughly 75% of these nearby galaxies, and completing this census will reveal insights into the stars making up a wide variety of galaxies, in a wide variety of environments. [Image Description: A galaxy, large and occupying most of the view from the centre. The whole galaxy is made of smooth, diffuse light. The galaxy is surrounded by a smoky grey halo. Many stars shine around the galaxy, on a black background.]

The glittering, glitzy contents of the globular cluster NGC 6652 sparkle in this star-studded image from the NASA/ESA Hubble Space Telescope. The core of the cluster is suffused with the pale blue light of countless stars, and a handful of particularly bright foreground stars are adorned with criss-crossing diffraction spikes. NGC 6652 lies in our own Milky Way galaxy in the constellation Sagittarius, just under 30 000 light-years from Earth and only 6500 light-years from the Galactic centre. Globular clusters are stable, tightly gravitationally bound clusters containing anywhere between tens of thousands and millions of stars. The intense gravitational attraction between the closely packed stars in globular clusters is what gives these star-studded objects their regular, spherical shape. This image combines data from two of Hubble’s third-generation instruments; the Advanced Camera for Surveys and Wide Field Camera 3. As well as two instruments, this image draws on two different observing programmes from two different teams of astronomers. The first team set out to survey globular clusters in the Milky Way galaxy in the hope of shedding light on topics ranging from the ages of these objects to the gravitational potential of the galaxy as a whole. The second team of astronomers used a trio of exquisitely sensitive filters in Hubble’s Wide Field Camera 3 to disentangle the proportions of carbon, nitrogen, and oxygen in globular clusters such as NGC 6652. [Image Description: A dense spherical cluster of stars. The stars merge into a bright core in the centre, and spread out to the edges gradually, giving way to an empty, dark background. Most of the stars are small points of light. A few stars with cross-shaped diffraction spikes appear larger, and stand out in front.]

Galactic island of tranquillity — The tranquil spiral galaxy UGC 12295 basks leisurely in this image from the NASA/ESA Hubble Space Telescope. This galaxy lies around 192 million light-years away in the constellation Pisces, and is almost face-on when viewed from Earth, displaying a bright central bar and tightly wound spiral arms. Despite appearing as an island of tranquillity in this image, UGC 12295 played host to a catastrophically violent explosion — a supernova — that was first detected in 2015. This supernova prompted two different teams of astronomers to propose Hubble observations of UGC 12295 that would sift through the wreckage of this vast stellar explosion. Supernovae are the explosive deaths of massive stars, and are responsible for forging many of the elements found here on Earth. The first team of astronomers used Hubble’s Wide Field Camera 3 (WFC3) to examine the detritus left behind by the supernova in order to better understand the evolution of matter in our Universe. The second team of astronomers also used WFC3 to explore the aftermath of UGC 12295’s supernova, but their investigation focused on returning to the sites of some of the best-studied nearby supernovae. Hubble’s keen vision can reveal lingering traces of these energetic events, shedding light on the nature of the systems that host supernovae. [Image Description: A broad spiral galaxy seen directly face-on. It has two bright spiral arms that extend from a bar, which shines from the very centre. Additional fainter arms branch off from these, studded with bright blue patches of star formation. Small, distant galaxies are dotted around it, on a dark background.]

Starstruck image of Arp 263 — The irregular galaxy Arp 263 lurks in the background of this image from the NASA/ESA Hubble Space Telescope, but the view is dominated by a stellar photobomber; the bright star BD+17 2217. Arp 263 — also known as NGC 3239 — is a patchy, irregular galaxy studded with regions of recent star formation, and astronomers believe that its ragged appearance is due to its having formed from the merger of two galaxies. It lies around 25 million light-years away in the constellation Leo. Two different Hubble investigations into Arp 263, using two of Hubble’s third-generation instruments, contributed data to this image. The first investigation was part of an effort to observe the sites of recent supernovae, such as the supernova SN 2012A that was detected just over a decade ago in Arp 263. Astronomers used Hubble’s powerful Wide Field Camera 3 to search for lingering remnants of the colossal stellar explosion. The second investigation is part of a campaign using Hubble’s Advanced Camera for Surveys to image all the previously unobserved peculiar galaxies in the Arp catalogue, including Arp 263, in order to find promising subjects for further study using the NASA/ESA/CSA James Webb Space Telescope. The interloping foreground star, BD+17 2217, is adorned with two sets of criss-crossing diffraction spikes. The interaction of light with Hubble’s internal structure means that concentrated bright objects such as stars are surrounded by four prominent spikes. Since this image of BD+17 2217 was created using two sets of Hubble data, the spikes from both images surround this stellar photobomber. The spikes are at different angles because Hubble was at different orientations when it collected the two datasets. [Image Description: An irregular galaxy that appears like a triangle-shaped patch of tiny stars. It is densest in the centre and along one edge, growing faint out to the opposite corner. Several bright pink patches mark areas of star formation, and the galaxy’s bright

Galactic monster mash — The NASA/ESA Hubble Space Telescope has captured a monster in the making in this observation of the exceptional galaxy cluster eMACS J1353.7+4329, which lies about eight billion light-years from Earth in the constellation Canes Venatici. This disturbed collection of at least two galaxy clusters is in the process of merging together to create a cosmic monster, a single gargantuan cluster acting as a gravitational lens. Gravitational lensing is a dramatic example of Einstein’s general theory of relativity in action. A celestial body such as a galaxy cluster is sufficiently massive to distort spacetime, which causes the path of light around the object to be visibly bent as if by a vast lens. Gravitational lensing can also magnify distant objects, allowing astronomers to observe objects that would otherwise be too faint and too far away to be detected. It can also distort the images of background galaxies, turning them into streaks of light. The first hints of gravitational lensing are already visible in this image as bright arcs which mingle with the throng of galaxies in eMACS J1353.7+4329. The data in this image are drawn from an observing proposal called Monsters in the Making, which used two of Hubble’s instruments to observe five exceptional galaxy clusters at multiple wavelengths. These multi-wavelength observations were made possible by Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys. The astronomers behind these observations hope to lay the groundwork for future studies of vast gravitational lenses with next-generation telescopes such as the NASA/ESA/CSA James Webb Space Telescope. [Image Description: A cluster of elliptical galaxies, visible as a dense crowd of oval shapes, each glowing orange around a bright core. Right of the largest, central galaxy, a background galaxy is stretched into two connected, thin arcs by the cluster’s gravity. Various other galaxies are dotted all around, a few being small spirals. A bright star with four long

Serene Supernova Aftermath — The spiral galaxy UGC 11860 seems to float serenely against a field of background galaxies in this image from the NASA/ESA Hubble Space Telescope. UGC 11860 lies around 184 million light-years away in the constellation Pegasus, and its untroubled appearance is deceiving; this galaxy recently played host to an almost unimaginably energetic stellar explosion. A supernova explosion — the catastrophically violent end of a massive star’s life — was detected in UGC 11860 in 2014 by a robotic telescope dedicated to scouring the skies for transient astronomical phenomena — astronomical objects that are only visible for a short period of time. Two different teams of astronomers used Hubble’s Wide Field Camera 3 to search through the aftermath and unpick the lingering remnants of this vast cosmic explosion. One team explored UGC 11860 to understand more about the progenitor star systems that eventually meet their demise in supernovae. The hugely energetic processes during supernova explosions are predominantly responsible for forging the elements between silicon and nickel on the periodic table. This means that understanding the influence of the masses and compositions of the progenitor star systems is vital to explaining how many of the chemical elements here on Earth originated. The other group of astronomers used Hubble to follow up supernovae that were detected by robotic telescopes. These automated eyes on the sky function without human intervention, and capture transient events in the night sky. Robotic telescopes allow astronomers to detect everything from unexpected asteroids to rare, unpredictable supernovae, and can identify intriguing objects that can then be investigated in more detail by powerful telescopes such as Hubble. [Image Description: A spiral galaxy, a fuzzy oval tilted diagonally and partially towards the viewer. The centre glows in warm colours, and has two prominent spiral arms around it, with bright points of star formation. The galaxy ap

On the edge of the Lagoon — The teeming stars of the globular cluster NGC 6544 glisten in this image from the NASA/ESA Hubble Space Telescope. This cluster of tightly bound stars lies more than 8000 light-years away from Earth and is — like all globular clusters — a densely populated region of tens of thousands of stars. This image of NGC 6544 combines data from two of Hubble’s instruments — the Advanced Camera for Surveys and Wide Field Camera 3 — as well as two separate astronomical observations. The first observation was designed to find a visible counterpart to the radio pulsar discovered in NGC 6544. A pulsar is the rapidly spinning remnant of a dead star, emitting twin beams of electromagnetic radiation like a vast astronomical lighthouse. This pulsar rotates particularly quickly, and astronomers turned to Hubble to help determine how this object evolved in NGC 6544. The second observation which contributed data to this image was also designed to find the visible counterparts of objects detected at other electromagnetic wavelengths. Instead of matching up sources to a pulsar, however, astronomers used Hubble to search for the counterparts of faint X-ray sources. Their observations could help explain how clusters like NGC 6544 change over time. NGC 6544 lies in the constellation Sagittarius, close to the vast Lagoon Nebula, a hazy labyrinth of gas and dust sculpted by the fierce winds of newly born stars. The Lagoon Nebula is truly colossal — even by astronomical standards — and measures 55 light-years across and 20 light-years from top to bottom. Previous Hubble images of the nebula incorporated infrared observations to reveal young stars and intricate structures that would be obscured at visible wavelengths by clouds of gas and dust. [Image Description: A cluster of stars in warm and cool colours. The whole view is filled with small stars, which become much denser and brighter around a core just right of centre. Most of the stars are small, but some are larger with a rou

A dishevelled irregular galaxy — The galaxy NGC 7292 billows across this image from the NASA/ESA Hubble Space Telescope, accompanied by a handful of bright stars and the indistinct smudges of extremely distant galaxies in the background. It lies around 44 million light-years from Earth in the constellation Pegasus. This slightly dishevelled galaxy is irregular, meaning that it lacks the distinct spiral arms of galaxies like the Whirlpool Galaxy or the smooth elliptical shape of galaxies like Messier 59. Unusually, its core is stretched out into a distinct bar, a feature seen in many spiral galaxies. Alongside its hazy shape, NGC 7292 is remarkably faint. As a result, astronomers classify NGC 7292 as a low surface brightness galaxy, barely distinguishable against the backdrop of the night sky. Such galaxies are typically dominated by gas and dark matter rather than stars. Astronomers directed Hubble to inspect NGC 7292 during an observational campaign studying the aftermath of Type II supernovae. These colossal explosions happen when a massive star collapses and then violently rebounds in a catastrophic explosion that tears the star apart. Astronomers hope to learn more about the diversity of Type II supernovae they have observed by scrutinising the aftermath and remaining nearby stars of a large sample of historical Type II supernovae. NGC 7292’s supernova was observed in 1964 and accordingly given the identifier SN 1964H. Studying the stellar neighbourhood of SN 1964H helps astronomers estimate the initial mass of the star that went supernova, and could uncover surviving stellar companions that once shared a system with the star that would become SN 1964H. [Image Description: A galaxy fills up most of the frame from the right. It is fuzzy and diffuse, but made up of numerous tiny stars. In the core, the stars merge into a glowing bar shape. The gas and stars in the galaxy vary between warm and cool colours. They are spread over a large area, the colours mixing like clouds. The glow of the galaxy

Under the Sea — The jellyfish galaxy JO206 trails across this image from the NASA/ESA Hubble Space Telescope, showcasing a colourful star-forming disc surrounded by a pale, luminous cloud of dust. A handful of bright stars with criss-cross diffraction spikes stand out against an inky black backdrop at the bottom of the image. JO206 lies over 700 million light-years from Earth in the constellation Aquarius, and this image of the galaxy is the sixth and final instalment in a series of observations of jellyfish galaxies. Some of Hubble's other observations of these peculiar galaxies — which range from grandiose to ghostly — are available here. Jellyfish galaxies are so-called because of their resemblance to their aquatic namesakes. In this image, the disc of JO206 is trailed by long tendrils of bright star formation that stretch towards the bottom right of this image, just as jellyfish trail tentacles behind them. The tendrils of jellyfish galaxies are formed by the interaction between galaxies and the intra-cluster medium, a tenuous superheated plasma that pervades galaxy clusters. As galaxies move through galaxy clusters they ram into the intracluster medium, which strips gas from the galaxies and draws it into the long tendrils of star formation. The tentacles of jellyfish galaxies give astronomers a unique opportunity to study star formation under extreme conditions, far from the influence of the main disc of the galaxy. Surprisingly, Hubble revealed that there are no striking differences between star formation in the discs of jellyfish galaxies and star formation in their tentacles, which suggests the environment of newly-formed stars has only a minor influence on their formation. [Image Description: A spiral galaxy that is tilted partially toward us. Its inner disc is bright and colourful, with bluish and reddish spots of star formation throughout the arms. An outer disc of pale, dim dust surrounds it. It has many arms, which are being pulled away from the disc, down and t

The spiral galaxy NGC 298 basks in this image from the NASA/ESA Hubble Space Telescope. NGC 298 lies around 89 million light-years away in the constellation Cetus, and appears isolated in this image — only a handful of distant galaxies and foreground stars accompany the lonely galaxy. While NGC 298 seems peaceful, in 1986 it was host to one of astronomy's most extreme events: a catastrophic stellar explosion known as a Type II supernova. Hubble’s Advanced Camera for Surveys captured NGC 298 as part of an investigation into the origins of Type II supernovae. All Type II supernovae are produced by the collapse and subsequent explosion of young, massive stars, but they can produce a spectacular diversity of brightnesses and spectral features. Astronomers suspect that the diversity of this cosmic firework show might be due to gas and dust being stripped from the stars that will eventually produce Type II supernovae. Observing the region surrounding supernova explosions can reveal traces of the progenitor star’s history preserved in this lost mass, as well as revealing any companion stars that survived the supernova. Hubble used the brief periods between scheduled observations to explore the aftermath of a number of Type II supernovae, hoping to piece together the relationship between Type II supernovae and the stellar systems which give rise to them. [Image description: A spiral galaxy. It is tilted diagonally, and slightly towards the viewer, making its core and disc separately visible. Its disc is speckled by small stars, has threads of dark reddish dust and bubbles of bright, glowing gas. The core shines brightly in a warmer colour. Several tiny stars and small galaxies are included in the black background.] Links Pan: Hubble explores explosive aftermath in NGC 298

A jellyfish galaxy adrift — The jellyfish galaxy JW39 hangs serenely in this image from the NASA/ESA Hubble Space Telescope. This galaxy lies over 900 million light-years away in the constellation Coma Berenices, and is one of several jellyfish galaxies that Hubble has been studying over the past two years. Despite this jellyfish galaxy’s serene appearance, it is adrift in a ferociously hostile environment; a galaxy cluster. Compared to their more isolated counterparts, the galaxies in galaxy clusters are often distorted by the gravitational pull of larger neighbours, which can twist galaxies into a variety of weird and wonderful shapes. If that was not enough, the space between galaxies in a cluster is also pervaded with a searingly hot plasma known as the intracluster medium. While this plasma is extremely tenuous, galaxies moving through it experience it almost like swimmers fighting against a current, and this interaction can strip galaxies of their star-forming gas. This interaction between the intracluster medium and the galaxies is called ram-pressure stripping, and is the process responsible for the trailing tendrils of this jellyfish galaxy. As JW39 has moved through the cluster the pressure of the intracluster medium has stripped away gas and dust into long trailing ribbons of star formation that now stretch away from the disc of the galaxy. Astronomers using Hubble’s Wide Field Camera 3 studied these trailing tendrils in detail, as they are a particularly extreme environment for star formation. Surprisingly, they found that star formation in the ‘tentacles’ of jellyfish galaxies was not noticeably different from star formation in the galaxy disc. [Image Description: A spiral galaxy. It is large in the centre with a lot of detail visible. The core glows brightly and is surrounded by concentric rings of dark and light dust. The spiral arms are thick and puffy with grey dust and glowing blue areas of star formation. They wrap around the galaxy to form a ring. Part of the arm is

Scrutinising a star-studded cluster — The densely packed globular cluster NGC 6325 glistens in this image from the NASA/ESA Hubble Space Telescope. This concentrated group of stars lies around 26 000 light years from Earth in the constellation Ophiuchus. Globular clusters like NGC 6325 are tightly bound collections of stars with anywhere from tens of thousands to millions of members. They can be found in all types of galaxies, and act as natural laboratories for astronomers studying star formation. This is because the constituent stars of globular clusters tend to form at roughly the same time and with similar initial composition, meaning that astronomers can use them to fine-tune their theories of how stars evolve. Astronomers inspected this particular cluster not to understand star formation, but to search for a hidden monster. Though it might look peaceful, astronomers suspect this cluster could contain an intermediate-mass black hole that is subtly affecting the motion of surrounding stars. Previous research found that the distribution of stars in some highly concentrated globular clusters — those with stars packed relatively tightly together — was slightly different from what astronomers expected. This discrepancy suggested that at least some of these densely packed globular clusters — including perhaps NGC 6325 — could have a black hole lurking at the centre. To explore this hypothesis further, astronomers turned to Hubble’s Wide Field Camera 3 to observe a larger sample of densely populated globular clusters, which included this star-studded image of NGC 6325. Additional data from Hubble’s Advanced Camera for Surveys were also incorporated into this image. [Image Description: A dense cluster of bright stars. The core of the cluster is to the left and has a distinct group of blue stars. Surrounding the core are a multitude of stars in warmer colours. These stars are very numerous near the core and become more and more sparse, and more small and distant, out to the sides of the image

Cosmic leviathan — A vast galaxy cluster lurks in the centre of this image from the NASA/ESA Hubble Space Telescope. Like a submerged sea monster causing waves on the surface, this cosmic leviathan can be identified by the distortions in spacetime around it. The mass of the cluster has caused the images of background galaxies to be gravitationally lensed; the galaxy cluster has caused a sufficient curvature of spacetime to bend the path of light and cause background galaxies to appear distorted into streaks and arcs of light. A host of other galaxies can be seen surrounding the cluster, and a handful of foreground stars with tell-tale diffraction spikes are scattered throughout the image. This particular galaxy cluster is called eMACS J1823.1+7822, and lies almost nine billion light-years away in the constellation Draco. It is one of five exceptionally massive galaxy clusters explored by Hubble in the hopes of measuring the strengths of these gravitational lenses and providing insights into the distribution of dark matter in galaxy clusters. Strong gravitational lenses like eMACS J1823.1+7822 can help astronomers study distant galaxies by acting as vast natural telescopes which magnify objects that would otherwise be too faint or distant to resolve. This multiwavelength image layers data from eight different filters and two different instruments: Hubble’s Advanced Camera for Surveys and Wide Field Camera 3. Both instruments have the ability to view astronomical objects in just a small slice of the electromagnetic spectrum using filters, which allow astronomers to image objects at precisely selected wavelengths. The combination of observations at different wavelengths lets astronomers develop a more complete picture of the structure, composition and behaviour of an object than visible light alone would reveal. [Image description: A cluster of large galaxies, surrounded by various stars and smaller galaxies on a dark background. The central cluster is mostly made of bright elliptical

The jellyfish galaxy JO175 appears to hang suspended in this image from the NASA/ESA Hubble Space Telescope. This galaxy lies over 650 million light-years from Earth in the appropriately-named constellation Telescopium, and was captured in crystal-clear detail by Hubble’s Wide Field Camera 3. A handful of more distant galaxies are lurking throughout the scene, and a bright four-pointed star lies to the lower right side. Jellyfish galaxies get their unusual name from the tendrils of star-forming gas and dust that trail behind them, just like the tentacles of a jellyfish. These bright tendrils contain clumps of star formation and give jellyfish galaxies a particularly striking appearance. Unlike their ocean-dwelling namesakes, jellyfish galaxies make their homes in galaxy clusters, and the pressure of the tenuous superheated plasma that permeates these galaxy clusters is what draws out the jellyfish galaxies’ distinctive tendrils. Hubble recently completed a deep dive into jellyfish clusters, specifically the star-forming clumps of gas and dust that stud their tendrils. By studying the origins and fate of the stars in these clumps, astronomers hoped to better understand the processes underpinning star formation elsewhere in the Universe. Interestingly, their research suggests that star formation in the discs of galaxies is similar to star formation in the extreme conditions found in the tendrils of jellyfish galaxies. [Image Description: A spiral galaxy. Its spiral arms are studded with many pink spots, especially around the top of the galaxy. One arm is sticking out below the galaxy. From it and around the bottom of the galaxy, faint gas streams away, while little gas is visible above the galaxy. The galaxy is quite small in the centre of a dark background, where a few smaller galaxies of various shapes and sizes hang.] Links Pan: Ghostly galactic jellyfish

The cluster that almost got away — A menagerie of interesting astronomical finds fill this image from the NASA/ESA Hubble Space Telescope. As well as several large elliptical galaxies, a ring-shaped galaxy is lurking on the right of this image. A pair of bright stars are also visible at the left of this image, notable for their colourful criss-crossing diffraction spikes. This collection of astronomical curiosities is the galaxy cluster ACO S520 in the constellation Pictor, which was captured by Hubble’s Advanced Camera for Surveys. This is one of a series of Hubble observations searching for massive, luminous galaxy clusters that had not been captured by earlier surveys. Appropriately, the proposal for observing time was named "They almost got away"! Astronomers took advantage of occasional gaps in Hubble's busy schedule to capture images of these barely-explored galaxy clusters, revealing a wealth of interesting targets for further study with Hubble and the NASA/ESA/CSA James Webb Space Telescope. Galaxy clusters are among the largest known objects in the Universe, and studying these objects can provide insights into the distribution of dark matter, which is responsible for most of the mass of a galaxy cluster. The vast masses of galaxy clusters is what causes many of them to act as gravitational lenses which distort and magnify light from even more distant objects. This can allow astronomers to use galaxy clusters as a kind of natural gravitational telescope to reveal distant objects that would usually be too faint to resolve — even for the crystal-clear vision of Hubble. [Image description: A collection of oval-shaped, elliptical galaxies. The largest has two neighbouring bright spots in the core. It and two others look like galaxy clusters, with surrounding smaller galaxies. On the left edge of the image are two bright stars with four long spikes, and on the right edge is a small ring-shaped galaxy. Smaller stars and galaxies are spread evenly across the dark background.] Links Pan: The clu

The barred spiral galaxy UGC 678 takes centre stage in this image from the NASA/ESA Hubble Space Telescope. The spectacular galaxy lies around 260 million light-years from Earth in the constellation Pisces and is almost face on, allowing its lazily winding spiral arms to stretch across this image. In the foreground, a smaller edge-on galaxy seems to bisect the upper portion of UGC 678. Just like humans, stars have a natural lifecycle; they are born, grow up, and eventually grow old and die. Studying this stellar life cycle — usually referred to as stellar evolution — is an important topic for astronomers. The ends of star lives can be marked by truly spectacular events, including titanic supernova explosions, the creation of unimaginably dense neutron stars, and even the birth of black holes. UGC 678 was recently found to be host to one of these events; in 2020 a robotic telescope scanning the night sky in search of dangerous asteroids discovered evidence of an enormous supernova explosion in the galaxy. Two separate Hubble observations turned to UGC 678 to scour the galaxy in search of the aftermath of its supernova explosion. One team of astronomers used Hubble’s Advanced Camera for Surveys, and the other the Wide Field Camera 3, but both aimed to explore UGC 678 in the hope of unearthing clues to the identity of the star that produced the 2020 supernova. [Image Description: A large spiral galaxy. It has many narrow arms that are tightly-twisted in the centre, but at the ends they point out in different directions. The galaxy’s core glows brightly, while its disc is mostly faint, but with bright blue spots throughout the arms. A few smaller spiral galaxies at varying angles are visible in front, and it is surrounded by other tiny stars and galaxies, on a black background.] Links Pan: Hubble spotlights a swirling spiral

A jellyfish and the ram — Here we see JO204, a ‘jellyfish galaxy’ so named for the bright tendrils of gas that appear in this image to be drifting lazily below JO204’s bright central bulk. The galaxy lies almost 600 million light-years away in the constellation Sextans. This image was captured by the NASA/ESA Hubble Space Telescope, and it is the third of a series of Pictures of the Week featuring jellyfish galaxies. This series of images is possible thanks to a survey in which observations were made of six of these fascinating galaxies, including JO204. This survey was performed with the intention of better understanding star formation under extreme conditions. Given the dreamy appearance of this image, it would be understandable to wonder why jellyfish galaxies should be such a crucible for star formation. The answer is that — as is often the case with astronomy — first appearances can be deceiving. Whilst the delicate ribbons of gas beneath JO204 may look like floating jellyfish tentacles, they are in fact the outcome of an intense astronomical process known as ram pressure stripping. Ram pressure is a particular type of pressure exerted on a body when it moves relative to a fluid. An intuitive example is the sensation of pressure you experience when you are standing in an intense gust of wind — the wind is a moving fluid, and your body feels pressure from it. An extension of this analogy is that your body will remain whole and coherent, but the more loosely bound things — like your hair and your clothes — will flap in the wind. The same is true for jellyfish galaxies. They experience ram pressure because of their movement against the intergalactic medium that fills the spaces between galaxies in a galaxy cluster. The galaxies experience intense pressure from that movement, and as a result their more loosely bound gas is stripped away. This gas is mostly the colder and denser gas in the galaxy — gas which, when stirred and compressed by the ram pressure, collapses and

The somewhat amorphous spiral galaxy UGC 2890 appears side-on in this image from the NASA/ESA Hubble Space Telescope, with bright foreground stars studding the image. This galaxy lies around 30 million light-years away in the constellation Camelopardalis. In 2009 astronomers spotted a catastrophically powerful supernova explosion in UGC 2890. While the supernova itself has long since faded from view, Hubble recently took a break from its regular observing schedule to inspect the aftermath of this explosive event. A Type II supernova is a spectacularly energetic explosion that marks the violent death of a massive star. As it runs out of the elements necessary to fuel nuclear fusion, the core of a massive star flickers out and stops producing energy. With nothing to support the crushing force of gravity, the core of the star shrinks and then suddenly implodes, leaving the star’s outer layers to collapse inwards and rebound out into space as a supernova explosion. This observation is one of many Hubble investigations of Type II supernovae. Astronomers turned to Hubble’s Advanced Camera for Surveys to explore the surroundings of Type II supernovae in the hope of discovering the ages and masses of stars in the neighbourhood. This will reveal insights into the types of stars that eventually create Type II supernovae, as well as revealing any stellar survivors of colossal supernova explosions. [Image description: A spiral galaxy is seen edge-on and tilted at an angle. The body of the galaxy is blue and obscured by threads of dark red dust, and it is surrounded by a pale glow. Three stars with prominent cross-shaped diffraction spikes are very bright in the foreground. The background is dark and sparsely-covered in small stars.] Links Pan: Aftermath of a cosmic explosion

Portrait of a galactic jellyfish — The galaxy JW100 features prominently in this image from the NASA/ESA Hubble Space Telescope, with streams of star-forming gas dripping from the disc of the galaxy like streaks of fresh paint. These tendrils of bright gas are formed by a process called ram pressure stripping, and their resemblance to dangling tentacles has led astronomers to refer to JW100 as a ‘jellyfish’ galaxy. It is located in the constellation Pegasus, over 800 million light-years away. Ram pressure stripping occurs when galaxies encounter the diffuse gas that pervades galaxy clusters. As galaxies plough through this tenuous gas it acts like a headwind, stripping gas and dust from the galaxy and creating the trailing streamers that prominently adorn JW100. The bright elliptical patches in the image are other galaxies in the cluster that hosts JW100. As well as JW100’s bright tendrils, this image also contains a remarkably bright area of diffuse light towards the top of this image which contains two bright blotches at its core. This is the core of IC 5338, the brightest galaxy in the galaxy cluster, known as a cD galaxy. It’s not unusual for cD galaxies to exhibit multiple nuclei, as they are thought to grow by consuming smaller galaxies, the nuclei of which can take a long time to be absorbed. The bright points of light studding its outer fringes are a rich population of globular clusters. This observation took advantage of the capabilities of Hubble’s Wide Field Camera 3, and is part of a sequence of observations designed to explore star formation in the tendrils of jellyfish galaxies. These tendrils represent star formation under extreme conditions, and could help astronomers understand the process of star formation elsewhere in the universe. [Image Description: A thin spiral galaxy is seen edge-on in the lower right. Its bulge and arms are very bright, mixing reddish and bluish light. Patchy blue trails extend below it, resembling tentacles, made from star-forming regions. Six sm

Hubble’s neighbourhood watch — UGCA 307 hangs against an irregular backdrop of distant galaxies in this image from the NASA/ESA Hubble Space Telescope. The small galaxy consists of a diffuse band of stars containing red bubbles of gas that mark regions of recent star formation, and lies roughly 26 million light-years from Earth in the constellation Corvus. Appearing as just a small patch of stars, UGCA 307 is a diminutive dwarf galaxy without a defined structure — resembling nothing more than a hazy patch of passing cloud. This image is part of a Hubble project to explore every known nearby galaxy, giving astronomers insights into our galactic neighbourhood. Before this set of observations, almost three quarters of nearby galaxies had been investigated by Hubble in enough detail to spot the brightest stars and build up an understanding of the stars populating each galaxy. This Hubble project set out to explore the remaining quarter of nearby galaxies by taking advantage of short gaps in Hubble’s observing schedule. This crystal-clear image was captured by Hubble’s Advanced Camera for Surveys (ACS), which was installed on the telescope in 2002 during Servicing Mission 3B. Hubble’s vantage point in low Earth orbit means that it is above atmospheric turbulence, giving it a sharper view of the Universe. However, it is also close enough to Earth that astronauts could visit the telescope to repair and refurbish the telescope. In total, five Space Shuttle missions flew to Hubble and kept it at the forefront of astronomy by installing new instruments. The ACS replaced one of Hubble’s original instruments, the Faint Object Camera, which was built by ESA. [Image description: A wide band of bluish light extends from the centre of the image to the right side. It is speckled with many tiny stars, and a few small, bright red bubbles of gas, identifying it as a galaxy. The background is black, and has small galaxies and stars spread around. Most are too small to distinguish, except for two oval-shap

Hubble spies a meandering spiral — The irregular spiral galaxy NGC 5486 hangs against a background of dim, distant galaxies in this image from the NASA/ESA Hubble Space Telescope. The tenuous disc of the galaxy is threaded through with pink wisps of star formation, which stand out from the diffuse glow of the galaxy’s bright core. While this particular galaxy has indistinct, meandering spiral arms it lies close to the much larger Pinwheel Galaxy, one of the best known examples of ‘grand design’ spiral galaxies with prominent and well-defined spiral arms. In 2006 Hubble captured an image of the Pinwheel Galaxy which was — at the time — the largest and most detailed photo of a spiral galaxy ever taken with Hubble. NGC 5486 lies 110 million light-years from Earth in the constellation Ursa Major. Constellations are not only patterns of bright stars, but also a system that astronomers use to divide the sky into regions. There are 88 of these regions, and each has an associated constellation depicting a mythological figure, an animal, or even an item of scientific equipment. This strange celestial menagerie contains everything from Ursa Major’s great bear to a toucan, a sea monster, a telescope, and even a painter's easel! This observation comes from a selection of Hubble images exploring the detritus left behind by Type II supernovae. As massive stars reach the end of their lives they cast off huge amounts of gas and dust before ending their lives in titanic supernova explosions. NGC 5486 hosted a supernova in 2004, and astronomers used the keen vision of Hubble’s Advanced Camera for Surveys to explore the aftermath in the hopes of learning more about these explosive events. [Image description: A spiral galaxy. It is irregularly-shaped and its spiral arms are difficult to distinguish. The edges are faint and the core has a pale glow. It is dotted with small, wispy, pink regions where stars are forming. A few stars and small galaxies in warm colours are visible around it.] Links Hubble spies

A jellyfish galaxy with trailing tentacles of stars hangs in inky blackness in this image from the NASA/ESA Hubble Space Telescope. As Jellyfish galaxies move through intergalactic space they are slowly stripped of gas, which trails behind the galaxy in tendrils illuminated by clumps of star formation. These blue tendrils are visible drifting below the core of this galaxy, and give it its jellyfish-like appearance. This particular jellyfish galaxy — known as JO201 — lies in the constellation Cetus, which is named after a sea monster from ancient Greek mythology. This sea-monster-themed constellation adds to the nautical theme of this image. The tendrils of jellyfish galaxies extend beyond the bright disc of the galaxy core. This particular observation comes from an investigation into the sizes, masses and ages of the clumps of star formation in the tendrils of jellyfish galaxies. Astronomers hope that this will provide a breakthrough in understanding the connection between ram-pressure stripping — the process that creates the tendrils of jellyfish galaxies — and star formation. This galactic seascape was captured by Wide Field Camera 3 (WFC3), a versatile instrument that captures images at ultraviolet and visible wavelengths. WFC3 is the source of some of Hubble’s most spectacular images, from a view of Jupiter and Europa to a revisit to the Pillars of Creation. [Image description: A spiral galaxy lies just off-centre. It has large, faint, reddish spiral arms and a bright, reddish core. These lie over two brighter blue spiral arms. These are patchy, with blotches of star formation. Long trails of these bright blotches trail down from the lower spiral arm, resembling tendrils. The background is black, lightly scattered with small galaxies and stars, and a larger elliptical galaxy in one corner.] Links First science paper in the Astrophysical Journal Second science paper in the Astrophysical Journal Zoom: Galactic Seascape

Cosmic Contortions — A massive galaxy cluster in the constellation Cetus dominates the centre of this image from the NASA/ESA Hubble Space Telescope. This image is populated with a serene collection of elliptical and spiral galaxies, but galaxies surrounding the central cluster — which is named SPT-CL J0019-2026 — appear stretched into bright arcs, as if distorted by a gargantuan magnifying glass. This cosmic contortion is called gravitational lensing, and it occurs when a massive object like a galaxy cluster has a sufficiently powerful gravitational field to distort and magnify the light from background objects. Gravitational lenses magnify light from objects that would usually be too distant and faint to observe, and so these lenses can extend Hubble’s view even deeper into the Universe. This observation is part of an ongoing project to fill short gaps in Hubble’s observing schedule by systematically exploring the most massive galaxy clusters in the distant Universe, in the hopes of identifying promising targets for further study with both Hubble and the NASA/ESA/CSA James Webb Space Telescope. This particular galaxy cluster lies at a vast distance of 4.6 billion light years from Earth. Each year, the Space Telescope Science Institute is inundated with observing proposals for Hubble, in which astronomers suggest targets for observation. Even after selecting only the very best proposals, scheduling observations of all of Hubble’s targets for a year is a formidable task. There is sometimes a small fraction of observing time left unused in Hubble’s schedule, so in its ‘spare time’ the telescope has a collection of objects to explore — including the lensing galaxy cluster shown in this image. [Image description: A cluster of large galaxies, surrounded by various stars and smaller galaxies on a dark background. The central cluster is mostly made of bright elliptical galaxies that are surrounded by a warm glow. Nearby the cluster is the stretched, distorted arc of a galaxy

Galactic Crash Course — A spectacular trio of merging galaxies in the constellation Boötes takes centre stage in this image from the NASA/ESA Hubble Space Telescope. These three galaxies are set on a collision course and will eventually merge into a single larger galaxy, distorting one another’s spiral structure through mutual gravitational interaction in the process. An unrelated foreground galaxy appears to float serenely alongside the collision, and the smudged shapes of much more distant galaxies are visible in the background. This colliding trio — known to astronomers as SDSSCGB 10189 — is a relatively rare combination of three large star-forming galaxies lying within only 50 000 light-years of one another. While that might sound like a safe distance, for galaxies this makes them extremely close neighbours! Our own galactic neighbours are much further away; Andromeda, the nearest large galaxy to the Milky Way, is more than 2.5 million light-years away from Earth. This observation was designed to help astronomers understand the origin of the largest, most massive galaxies in the universe. These galactic behemoths are called Brightest Cluster Galaxies (BCGs) and — as the name suggests — are defined as the brightest galaxies in any given galaxy cluster. Astronomers suspect that BCGs form through the merger of large, gas-rich galaxies like the ones in this image. They turned to Hubble’s Wide Field Camera 3 and Advanced Camera for Surveys to investigate this galactic trio in painstaking detail, hoping to shed light on the formation of the Universe’s most massive galaxies. [Image description: Three galaxies stand together just right of centre. They are close enough that they appear to be merging into one. Their shapes are distorted, with strands of gas and dust running between them. Each is emitting a lot of light. Further to the left is an unconnected, dimmer spiral galaxy. The background is dark, with a few smaller, dim and faint galaxies and a couple of stars.] Links Vid

Can You Spot It? — Right in the middle of this image, nestled amongst a smattering of distant stars and even more distant galaxies, lies the newly discovered dwarf galaxy known as Donatiello II. If you cannot quite distinguish the clump of faint stars that is all we can see of Donatiello II in this image, then you are in good company. Donatiello II is one of three newly discovered galaxies that were so difficult to spot that they were all missed by an algorithm designed to search astronomical data for potential galaxy candidates. Even the best algorithms have their limitations when it comes to distinguishing very faint galaxies from individual stars and background noise. In these most challenging identification cases, discovery has to be done the old-fashioned way — by a dedicated human trawling through the data themselves. The data that enabled these discoveries was collected by the Dark Energy Survey (DES), an intense observation effort that spanned six years, and was carried out using the Dark Energy Camera (DECam), which is mounted on the Víctor M. Blanco 4-metre Telescope at Cerro Tololo Inter-American Observatory, a Program of NSF’s NOIRLab. As is the case for most major telescopes that receive public funding, the DES data were made available to the public. That is when the experienced amateur astronomer Giuseppe Donatiello stepped in. He laboriously processed and analysed chunks of the DES data, and made his discovery — three very faint galaxies, now named Donatiello II, III and IV respectively. All three are satellites of the well known Sculptor galaxy (otherwise known as NGC 253), meaning that they are all bound gravitationally to their much more massive companion. This image comes from an observing programme from the NASA/ESA Hubble Space Telescope. Based on their own independent search, a team led by Burçin Mutlu-Pakdil used Hubble to obtain long-exposure images of several faint galaxies, including Donatiello II. With the Hubble images, they were able to confirm

Tempestuous Young Stars in Orion — The bright variable star V 372 Orionis takes centre stage in this image from the NASA/ESA Hubble Space Telescope, which has also captured a smaller companion star in the upper left of this image. Both stars lie in the Orion Nebula, a colossal region of star formation roughly 1450 light years from Earth. V 372 Orionis is a particular type of variable star known as an Orion Variable. These young stars experience some tempestuous moods and growing pains, which are visible to astronomers as irregular variations in luminosity. Orion Variables are often associated with diffuse nebulae, and V 372 Orionis is no exception; the patchy gas and dust of the Orion Nebula pervade this scene. This image overlays data from two of Hubble’s instruments. Data from the Advanced Camera for Surveys and Wide Field Camera 3 at infrared and visible wavelengths were layered to reveal rich details of this corner of the Orion Nebula. Hubble also left its own subtle signature on this astronomical portrait in the form of the diffraction spikes surrounding the bright stars. These prominent artefacts are created by starlight interacting with Hubble’s inner workings, and as a result they reveal hints of Hubble’s structure. The four spikes surrounding the stars in this image are created by four vanes inside Hubble supporting the telescope’s secondary mirror. The diffraction spikes of the NASA/ESA/CSA James Webb Space Telescope, on the other hand, are six-pointed as a result of Webb’s hexagonal mirror segments and 3-legged support structure for the secondary mirror. [Image description: Two very bright stars with cross-shaped diffraction spikes are prominent: the larger is slightly lower-right of centre, the smaller lies towards the upper-left corner. Small red stars with short diffraction spikes are scattered around them. The background is covered nearly completely by gas: smoky, bright blue gas around the larger star in the centre and lower-right, and wispier red gas elsewhere.] Links

Visitor to a Galaxy — A host of astronomical objects throng this image from the NASA/ESA Hubble Space Telescope. Background galaxies ranging from stately spirals to fuzzy ellipticals are strewn across the image, and bright foreground stars much closer to home are also present, surrounded by diffraction spikes. In the centre of the image, the vague shape of the small galaxy UGC 7983 appears as a hazy cloud of light. UGC 7983 is around 30 million light-years from Earth in the constellation Virgo, and is a dwarf irregular galaxy — a type thought to be similar to the very earliest galaxies in the Universe. This image also conceals an astronomical interloper. A minor asteroid, only a handful of kilometres across, can be seen streaking across the upper left-hand side of this image. The trail of the asteroid is visible as four streaks of light separated by small gaps. These streaks of light represent the four separate exposures that were combined to create this image, the small gaps between each observation being necessary to change the filters inside Hubble’s Advanced Camera for Surveys. Capturing an asteroid was a fortunate side effect of a larger effort to observe every known galaxy close to the Milky Way. When this project was first proposed, roughly 75% of all the Milky Way’s near galactic neighbours had been imaged by Hubble. A group of astronomers proposed using the gaps between longer Hubble observations to capture images of the remaining 25%. The project was an elegantly efficient way to fill out some gaps not only in Hubble's observing schedule, but also in our knowledge of nearby galaxies.

This image from the NASA/ESA Hubble Space Telescope features the galaxy LEDA 48062 in the constellation Canes Venatici. LEDA 48062 is the faint, sparse, amorphous galaxy on the right side of this image, and it is accompanied by a more sharply defined neighbour on the left, the large, disc-like lenticular galaxy UGC 8603. A smattering of more distant galaxies also litter the background, and a handful of foreground stars are also visible throughout the image. Have you ever wondered why the stars in Hubble images are surrounded by four sharp points? These are called diffraction spikes, and are created when starlight diffracts — or spreads around — the support structures inside reflecting telescopes like Hubble. The four spikes are due to the four thin vanes supporting Hubble’s secondary mirror and are only noticeable for bright objects like stars where a lot of light is concentrated on one spot. Darker, more spread-out objects like the galaxies LEDA 48062 and UGC 8603 do not possess visible diffraction spikes. Hubble recently spent some time with our galactic neighbours. LEDA 48062 is only around 30 million light-years from the Milky Way, and was therefore included in the observing campaign Every Known Nearby Galaxy. The aim of this campaign was to observe precisely that: every known galaxy within 10 megaparsecs (around 33 million light-years) of the Milky Way. By getting to know our galactic neighbours, astronomers can determine what types of stars reside in various galaxies and also map out the local structure of the Universe. [Image description: A faint, scattered collection of cool stars in the form of an irregular galaxy lies right of centre. A disc-shaped galaxy viewed nearly edge-on lies to the left, surrounded by a wide glow. Several smaller galaxies in various orientations cluster around the two. The background is black and mostly empty.] Links Video of Calling on a Galactic Neighbour

The scattered stars of the globular cluster NGC 6355 are strewn across this image from the NASA/ESA Hubble Space Telescope. This globular cluster lies less than 50,000 light-years from Earth in the Ophiuchus constellation. NGC 6355 is a galactic globular cluster that resides in our Milky Way galaxy's inner regions. Globular clusters are stable, tightly bound clusters of tens of thousands to millions of stars, and can be found in all types of galaxies. Their dense populations of stars and mutual gravitational attraction give these clusters a roughly spherical shape, with a bright concentration of stars surrounded by an increasingly sparse sprinkling of stars. The dense, bright core of NGC 6355 was picked out in crystal-clear detail by Hubble in this image, and is the crowded area of stars towards the centre of this image. With its vantage point above the distortions of the atmosphere, Hubble has revolutionised the study of globular clusters. It is almost impossible to distinguish the stars in globular clusters from one another with ground-based telescopes, but astronomers have been able to use Hubble to study the constituent stars of globular clusters in detail. This Hubble image of NGC 6355 contains data from both the Advanced Camera for Surveys and Wide Field Camera 3. [Image description: A dense collection of stars covers the view. Towards the centre the stars become even more dense in a circular region, and also more blue. Around the edges there are some redder foreground stars, and many small stars in the background.] Links Video of Stargazing in NGC 6355

The highly irregular galaxy ESO 174-1, which resembles a lonely, hazy cloud against a backdrop of bright stars, dominates this image from the NASA/ESA Hubble Space Telescope. ESO 174-1 lies around 11 million light-years from Earth and consists of a bright cloud of stars and a faint, meandering tendril of dark gas and dust. This image is part of a collection of Hubble observations that aims to get to know our nearby galactic neighbours. To be more precise, the observations aim to resolve the brightest stars and basic properties of every known galaxy within 10 megaparsecs. A parsec is a unit used by astronomers to measure the vast distances to other galaxies — 10 megaparsecs translates to 32 million light-years — and makes astronomical distances easier to handle. For example, the nearest star to the Sun, Proxima Centauri, is about 1.3 parsecs away. In everyday units this is a staggering 40 million million kilometres! The programme to capture all of our neighbouring galaxies was designed to use the 2-3% of Hubble time that absolutely no other observing programme can use. Many of the myriad objects that Hubble observes can only be seen at certain times of year, which makes filling out the observatory’s schedule a daunting logistical challenge. Observing programmes such as the one which captured ESO 174-1 help Hubble’s operators get the most out of every last minute of observing time. [Image Description: A galaxy, large and occupying most of the view from the centre. The whole galaxy is made of smooth, diffuse light. In the centre it is brighter and bluer, fading to a pale grey halo that is faint and see-through. The light forms an arm on one side that curls around the top. A couple threads of dark dust cross the centre. Many stars shine around the galaxy, on a black background.] Links Pan: Hubble checks in on the neighbours

Everything, in one place, all at once — This luminous Picture of the Week shows Z 229-15 — imaged here in beautiful detail by the NASA/ESA Hubble Space Telescope — a celestial object that lies about 390 million light-years from Earth in the constellation Lyra. Z 229-15 is one of those interesting celestial objects that, should you choose to research it, you will find defined as several different things: sometimes as an active galactic nucleus (an AGN); sometimes as a quasar; and sometimes as a Seyfert galaxy. Which of these is Z 229-15 really? The answer is that it is all of these things all at once, because these three definitions have significant overlap. AGNs and quasars are both described in detail in the Hubble Word Bank, but in essence an AGN is a small region at the heart of certain galaxies (called active galaxies) that is far brighter than just the galaxy’s stars would be. The extra luminosity is due to the presence of a supermassive black hole at the galaxy’s core. Material sucked into a black hole actually doesn’t fall directly into it, but instead is drawn into a swirling disc, from where it is inexorably tugged towards the black hole. This disc of matter gets so hot that it releases a large amount of energy across the electromagnetic spectrum, and that’s what makes AGNs appear so bright. Quasars are a particular type of AGN; they are typically both extremely bright and extremely distant from Earth — several hundred million light-years is considered nearby for a quasar, making Z 229-15 positively local. Often an AGN is so bright that the rest of the galaxy cannot be seen, but Seyfert galaxies are active galaxies that host very bright AGNs (quasars) while the rest of the galaxy is still observable. So Z 229-15 is a Seyfert galaxy that contains a quasar, and that, by definition, hosts an AGN. Classification in astronomy can be a challenge! [Image Description: A spiral galaxy. It has two almost-straight arms coming from the left and right of the core that meet a starry ring arou

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Témata: 2023, fotografie, 5, 2

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