Picture of the Week

4 February 2019: This atmospheric image shows a galaxy named Messier 85, captured in all its delicate, hazy glory by the NASA/ESA Hubble Space Telescope. Messier 85 slants through the constellation of Coma Berenices (Berenice’s Hair), and lies around 50 million light-years from Earth. It was first discovered by Charles Messier’s colleague Pierre Méchain in 1781, and is included in the Messier catalogue of celestial objects. Messier 85 is intriguing — its properties lie somewhere between those of a lenticular and an elliptical galaxy, and it appears to be interacting with two of its neighbours: the beautiful spiral NGC 4394, located out of frame to the upper left, and the small elliptical MCG 3-32-38, located out of frame to the centre bottom. The galaxy contains some 400 billion stars, most of which are very old. However, the central region hosts a population of relatively young stars of just a few billion years …

28 January 2019: This striking image combines data gathered with the Advanced Camera for Surveys, installed on the NASA/ESA Hubble Space Telescope and data from the Subaru Telescope in Hawaii. It shows just a part of the spectacular tail emerging from a spiral galaxy nicknamed D100. Tails such as these are created by a process known as ram-pressure stripping. Despite appearances, the space between galaxies in a cluster is far from empty; it is actually filled with superheated gas and plasma, which drags and pulls at galaxies as they move through it, a little like the resistance one experiences when wading through deep water. This can be strong enough to tear galaxies apart, and often results in objects with peculiar, bizarre shapes and features — as seen here. D100’s eye-catching tail of gas, which stretches far beyond this image to the left, is a particularly striking example of this phenomenon. The galaxy is …

10 December 2018: This stunning spiral galaxy is Messier 100 in the constellation Coma Berenices, captured here by the NASA/ESA Hubble Space Telescope — not for the first time. Among Hubble’s most striking images of Messier 100 are a pair taken just over a month apart, before and after Servicing Mission 1, which took place 25 years ago in December 1993. After Hubble was launched, the astronomers and engineers operating the telescope found that the images it returned were fuzzy, as if it were out of focus. In fact, that was exactly what was happening. Hubble’s primary mirror functions like a satellite dish; its curved surface reflects all the light falling on it to a single focal point. However, the mirror suffered from a defect known as a spherical aberration, meaning that the light striking the edges of the mirror was not travelling to the same point as the light from the centre. …

26 November 2018: This dark, tangled web is an object named SNR 0454-67.2. It formed in a very violent fashion — it is a supernova remnant, created after a massive star ended its life in a cataclysmic explosion and threw its constituent material out into surrounding space. This created the messy formation we see in this NASA/ESA Hubble Space Telescope image, with threads of red snaking amidst dark, turbulent clouds. SNR 0454-67.2 is situated in the Large Magellanic Cloud, a dwarf spiral galaxy that lies close to the Milky Way. The remnant is likely the result of a Type Ia supernova explosion; this category of supernovae is formed from the death of a white dwarf star, which grows and grows by siphoning material from a stellar companion until it reaches a critical mass and then explodes. As they always form via a specific mechanism — when the white dwarf hits a particular mass …

22 October 2018: This Picture of the Week shows the unbarred spiral galaxy NGC 5033, located about 40 million light-years away in the constellation of Canes Venatici (The Hunting Dogs). The galaxy is similar in size to our own galaxy, the Milky Way, at just over 100 000 light-years across. Like in the Milky Way NGC 5033’s spiral arms are dotted with blue regions, indicating ongoing star formation. The blue patches house hot, young stars in the process of forming, while the older, cooler stars populating the galaxy’s centre cause it to appear redder in colour. In contrast to the Milky Way NGC 5033 is missing a central bar. Instead it has a bright and energetic core called an active galactic nucleus, which is powered by a supermassive black hole. This active nucleus gives it the classification of a Seyfert galaxy. Due to the ongoing activity the core of NGC 5033 shines bright …

8 October 2018: This image from the NASA/ESA Hubble Space Telescope reveals a spiral galaxy named Messier 95 (also known as M95 or NGC 3351). Located about 35 million light-years away in the constellation of Leo (The Lion), this swirling spiral was discovered by astronomer Pierre Méchain in 1781, and catalogued by French astronomer Charles Messier just four days later. Messier was primarily a comet hunter, and was often left frustrated by objects in the sky that resembled comets but turned out not to be. To help other astronomers avoid confusing these objects in the future, he created his famous catalogue of Messier objects. Most definitely not a comet, Messier 95 is actually a barred spiral galaxy. The galaxy has a bar cutting through its centre, surrounded by an inner ring currently forming new stars. Also our own Milky Way is a barred spiral. As well as hosting this stellar nursery, Messier 95 …

17 September 2018: In the northern constellation of Coma Berenices (Berenice's Hair) lies the impressive Coma Cluster — a structure of over a thousand galaxies bound together by gravity. Many of these galaxies are elliptical types, as is the brighter of the two galaxies dominating this image: NGC 4860 (centre). However, the outskirts of the cluster also host younger spiral galaxies that proudly display their swirling arms. Again, this image shows a wonderful example of such a galaxy in the shape of the beautiful NGC 4858, which can be seen to the left of its bright neighbour and which stands out on account of its unusual, tangled, fiery appearance. NGC 4858 is special. Rather than being a simple spiral, it is something called a “galaxy aggregate”, which is, just as the name suggests, a central galaxy surrounded by a handful of luminous knots of material that seem to stem from it, extending and …

10 September 2018: Gravity is so much a part of our daily lives that it is all too easy to forget its awesome power — but on a galactic scale, its power becomes both strikingly clear and visually stunning. This image was taken with the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3) and shows an object named SDSS J1138+2754. It acts as a gravitational lens illustrates the true strength of gravity: A large mass — a galaxy cluster in this case — is creating such a strong gravitational field that it is bending the very fabric of its surroundings. This causes the billion-year-old light from galaxies sitting behind it to travel along distorted, curved paths, transforming the familiar shapes of spirals and ellipticals (visible in other parts of the image) into long, smudged arcs and scattered dashes. Some distant galaxies even appear multiple times in this image. Since galaxies are wide …

3 September 2018: This week’s NASA/ESA Hubble Space Telescope image showcases the galaxy NGC 4036: a lenticular galaxy some 70 million light-years away in the constellation of Ursa Major (the Great Bear). This galaxy is known for its irregular lanes of dust, which form a swirling spiral pattern around the centre of the galaxy. This core is surrounded by an extended, hazy aura of gas and dust that stretches further out into space and causes the warm, fuzzy glow that can be seen here. The centre itself is also intriguing; it is something known as a LINER-type (Low-Ionisation Nuclear Emission-line Region) galactic nucleus, meaning that it displays particular emission lines within its spectrum. The particularly bright star visible slightly to the right of the galactic centre is not within the galaxy itself; it sits between us and NGC 4036, adding a burst of brightness to the scene. Due to its relative brightness, this …

13 August 2018: Galaxies abound in this spectacular Hubble image; spiral arms swirl in all colours and orientations, and fuzzy ellipticals can be seen speckled across the frame as softly glowing smudges on the sky. Each visible speck of a galaxy is home to countless stars. A few stars closer to home shine brightly in the foreground, while a massive galaxy cluster nestles at the very centre of the image; an immense collection of maybe thousands of galaxies, all held together by the relentless force of gravity. Galaxy clusters are some of the most interesting objects in the cosmos. They are the nodes of the cosmic web that permeates the entire Universe — to study them is to study the organisation of matter on the grandest of scales. Not only are galaxy clusters ideal subjects for the study of dark matter and dark energy, but they also allow the study of farther-flung galaxies. …

23 July 2018: This image taken by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 (WFC3) shows a beautiful spiral galaxy called NGC 6744. At first glance, it resembles our Milky Way albeit larger, measuring more than 200 000 light-years across compared to 100 000 light-year diameter for our home galaxy. NGC 6744 is similar to our home galaxy in more ways than one. Like the Milky Way, NGC 6744 has a prominent central region packed with old yellow stars. Moving away from the galactic core, one can see parts of the dusty spiral arms painted in shades of pink and blue; while the blue sites are full of young star clusters, the pink ones are regions of active star formation, indicating that the galaxy is still very lively. In 2005, a supernova, named 2005at, was discovered within NGC 6744, adding to the argument of this galaxy’s liveliness (not visible in this …

2 July 2018: This busy image is a treasure trove of wonders. Bright stars from the Milky Way sparkle in the foreground, the magnificent swirls of several spiral galaxies are visible across the frame, and a glowing assortment of objects at the centre make up a massive galaxy cluster. Such clusters are the biggest objects in the Universe that are held together by gravity, and can contain thousands of galaxies of all shapes and sizes. Typically, they have a mass of about one million billion times the mass of the Sun — unimaginably huge! Their incredible mass makes clusters very useful natural tools to test theories in astronomy, such as Einstein’s theory of general relativity. This tells us that objects with mass warp the fabric of spacetime around them; the more massive the object, the greater the distortion. An enormous galaxy cluster like this one therefore has a huge influence on the spacetime …

18 June 2018: In astronomy, the devil is in the details — as this image, taken by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys and Wide-Field Camera 3, demonstrates. The numerous fuzzy blobs and glowing shapes scattered across this image make up a galaxy cluster named RXC J0949.8+1707. Located to the upper right of the frame sits an especially beautiful and interesting barred spiral galaxy, seen face-on. In the past decade, astronomers peering at this galaxy have possibly discovered not one but three examples of a cosmic phenomenon known as a supernova, the magnificently bright explosion of a star nearing the end of its life. The newest supernova candidate is nicknamed SN Antikythera, and can be seen to the lower right of the host galaxy. This shone brightly in visible and infrared light over a number of years before fading slightly. The two other supernovae, nicknamed SN Eleanor and SN Alexander, …

21 May 2018: At first glance, this image is dominated by the vibrant glow of the swirling spiral to the lower left of the frame. However, this galaxy is far from the most interesting spectacle here — behind it sits a galaxy cluster. Galaxies are not randomly distributed in space; they swarm together, gathered up by the unyielding hand of gravity, to form groups and clusters. The Milky Way is a member of the Local Group, which is part of the Virgo Cluster, which in turn is part of the 100 000-galaxy-strong Laniakea Supercluster. The galaxy cluster seen in this image is known as SDSS J0333+0651. Clusters such as this can help astronomers understand the distant — and therefore early — Universe. SDSS J0333+0651 was imaged as part of a study of star formation in far-flung galaxies. Star-forming regions are typically not very large, stretching out for a few hundred light-years at most, …

14 May 2018: Resembling a wizard’s staff set aglow, NGC 1032 cleaves the quiet darkness of space in two in this image from the NASA/ESA Hubble Space Telescope. NGC 1032 is located about a hundred million light years away in the constellation Cetus (The Sea Monster). Although beautiful, this image perhaps does not do justice to the galaxy’s true aesthetic appeal: NGC 1032 is actually a spectacular spiral galaxy, but from Earth, the galaxy’s vast disc of gas, dust and stars is seen nearly edge-on. A handful of other galaxies can be seen lurking in the background, scattered around the narrow stripe of NGC 1032. Many are oriented face-on or at tilted angles, showing off their glamorous spiral arms and bright cores. Such orientations provide a wealth of detail about the arms and their nuclei, but fully understanding a galaxy’s three-dimensional structure also requires an edge-on view. This gives astronomers an overall idea …

23 April 2018: This pretty, cloud-like object may not look much like a galaxy — it lacks the well-defined arms of a spiral galaxy, or the reddish bulge of an elliptical — but it is in fact something known as a lenticular galaxy. Lenticular galaxies sit somewhere between the spiral and elliptical types; they are disc-shaped, like spirals, but they no longer form large numbers of new stars and thus contain only ageing populations of stars, like ellipticals. NGC 2655’s core is extremely luminous, resulting in its additional classification as a Seyfert galaxy: a type of active galaxy with strong and characteristic emission lines. This luminosity is thought to be produced as matter is dragged onto the accretion disc of a supermassive black hole sitting at the centre of NGC 2655. The structure of NGC 2655’s outer disc, on the other hand, appears calmer, but it is oddly-shaped. The complex dynamics of the …

2 April 2018: This image is packed full of galaxies! A keen eye can spot exquisite ellipticals and spectacular spirals, seen at various orientations: edge-on with the plane of the galaxy visible, face-on to show off magnificent spiral arms, and everything in between. The vast majority of these specks are galaxies, but to spot a foreground star from our own galaxy, you can look for a point of light with tell-tale diffraction spikes. The galaxies within the image are almost all part of a galaxy cluster — a monstrous collection of hundreds of galaxies all shackled together in the unyielding grip of gravity — with the charming name of SDSSJ0146-0929. The mass of this galaxy cluster is large enough to severely distort the spacetime, creating the odd, looping curves that almost encircle the central regions of the cluster. These graceful arcs are examples of a cosmic phenomenon known as an Einstein ring. The …

26 March 2018: This image, captured by the Advanced Camera for Surveys (ACS) on the NASA/ESA Hubble Space Telescope, shows the spiral galaxy NGC 5714, about 130 million light-years away in the constellation of Boötes (the Herdsman). NGC 5714 is classified as a Sc spiral galaxy, but its spiral arms — the dominating feature of spiral galaxies — are almost impossible to see, as NGC 5714 presents itself at an almost perfectly edge-on angle. Discovered by William Herschel in 1787, NGC 5714 was host to a fascinating and rare event in 2003. A faint supernova appeared about 8000 light-years below the central bulge of NGC 5714. Supernovae are the huge, violent explosions of dying stars, and the one that exploded in NGC 5714 — not visible in this much later image — was classified as a Type Ib/c supernova and named SN 2003dr. It was particularly interesting because its spectrum showed strong signatures …

12 March 2018: This stunning image from Hubble shows the majestic galaxy NGC 1015, found nestled within the constellation of Cetus (The Whale) 118 million light-years from Earth. In this image, we see NGC 1015 face-on, with its beautifully symmetrical swirling arms and bright central bulge creating a scene akin to a sparkling Catherine wheel firework. NGC 1015 has a bright, fairly large centre and smooth, tightly wound spiral arms and a central “bar” of gas and stars. This shape leads NGC 1015 to be classified as a barred spiral galaxy — just like our home, the Milky Way. Bars are found in around two-thirds of all spiral galaxies, and the arms of this galaxy swirl outwards from a pale yellow ring encircling the bar itself. Scientists believe that any hungry black holes lurking at the centre of barred spirals funnel gas and energy from the outer arms into the core via these …

5 March 2018: This enchanting spiral galaxy can be found in the constellation of Ursa Major (the Great Bear). Star-studded NGC 3972 lies about 65 million light-years away from the Earth, meaning that the light that we see now left it 65 million years ago, just when the dinosaurs became extinct. NGC 3972 has had its fair share of dramatic events. In 2011 astronomers observed the explosion of a type Ia supernova in the galaxy (not visible in this image). These dazzling objects all peak at the same brightness, and are brilliant enough to be seen over large distances. NGC 3972 also contains many pulsating stars called Cepheid variables. These stars change their brightness at a rate matched closely to their intrinsic luminosity, making them ideal cosmic lighthouses for measuring accurate distances to relatively nearby galaxies. Astronomers search for Cepheid variables in nearby galaxies which also contain a type Ia supernova so they …