Picture of the Week

23 October 2023: 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 …

16 October 2023: 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 …

9 October 2023: 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 …

25 September 2023: 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 …

18 September 2023: 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 …

11 September 2023: 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 …

4 September 2023: 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 …

7 August 2023: 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 …

24 July 2023: 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 …

10 July 2023: 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 …

3 July 2023: 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 …

12 June 2023: 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 …

5 June 2023: 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 …

29 May 2023: 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 …

22 May 2023: 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 …

1 May 2023: 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 …

17 April 2023: 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 …

10 April 2023: 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 …

3 April 2023: 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 …

27 March 2023: 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 …