Picture of the Week

8 January 2024: This Hubble Picture of the Week features Arp 122, a peculiar galaxy that in fact comprises two galaxies — NGC 6040, the tilted, warped spiral galaxy and LEDA 59642, the round, face-on spiral — that are in the midst of a collision. This dramatic cosmic encounter is located at the very safe distance of roughly 570 million light-years from Earth. Peeking in at the corner is the elliptical galaxy NGC 6041, a central member of the galaxy cluster that Arp 122 resides in, but otherwise not participating in this monster merger. Galactic collisions and mergers are monumentally energetic and dramatic events, but they take place on a very slow timescale. For example, the Milky Way is on track to collide with its nearest galactic neighbour, the Andromeda Galaxy (M31), but these two galaxies have a good four billion years to go before they actually meet. The process of colliding and …

1 January 2024: What are we looking at when we study this image? A very distant galaxy that lies 19.5 billion light-years from Earth? Or a much closer luminous red galaxy that is a (relatively) small 2.7 billion light-years away? Or a third galaxy that appears to be fairly close to the second? The answer, perhaps confusingly, is that we are looking at all three. More precisely, we are looking at light emitted from all of those galaxies, even though the most distant galaxy lies directly behind the first as seen from Earth. In fact, it is that very alignment that makes the particular visuals in this image possible. The central bright dot in this image is one of the closer galaxies, known by the lengthy — but informative — name of SDSS J020941.27+001558.4 (galaxy names in this format provide precise information about their location in the sky). The other bright dot above …

25 December 2023: 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 …

18 December 2023: 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 …

11 December 2023: 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 …

4 December 2023: 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 …

27 November 2023: 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 …

20 November 2023: 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 …

13 November 2023: 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 …

6 November 2023: 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 …

30 October 2023: 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 …

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 …

2 October 2023: 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 …

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 …

28 August 2023: 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 …