Galaxy Cluster Abell 3574

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The galaxy cluster Abell 3574 is captured here by the 570-megapixel Department of Energy-fabricated Dark Energy Camera (DECam) on the Víctor M. Blanco 4-meter Telescope, one of around 40 telescopes at the U.S. National Science Foundation Cerro Tololo Inter-American Observatory (CTIO) in Chile, a Program of NSF NOIRLab.

Located about 200 million light-years away, Abell 3574 is a gravitationally-bound group of hundreds of galaxies. Galaxy clusters are the second-largest-scale structures known in the Universe, but even at their massive scale these galaxies are never all that far from each other. In the top left, the large galaxy IC 4329, surrounded by rings of light, shows evidence of a past cosmic collision. The spread-out fragments of illuminated blue and white gas on the right side of the image are evidence of a similar clash with the galaxy NGC 5291 (yellow color). If you look closely, you can see more evidence of gravitationally interacting galaxies. Do you notice any?

The camera that captured this image was specifically designed for the Dark Energy Survey (DES) and was operated by the Department of Energy (DOE) and NSF between 2013 and 2019. The purpose of DES was to map out hundreds of millions of galaxies and record their distances to help astronomers understand dark energy. Since the conclusion of DES, the DES data have been made available to the public and the DECam has been available to other researchers on the Blanco telescope.

Image Credit: Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA

Image processing: R. Colombari, M. Zamani (NSF NOIRLab) and T.A. Rector (University of Alaska Anchorage/NSF NOIRLab)

Image enhancement: Jean-Baptiste Faure

Dwarf Galaxies NGC 4490 and NGC 4485 by Webb

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For this new Webb picture, the James Webb Space Telescope has spied a pair of dwarf galaxies engaged in a gravitational dance. These two galaxies are named NGC 4490 and NGC 4485, and they're located about 24 million light-years away in the constellation Canes Venatici (The Hunting Dogs). Aside from the Milky Way's own dwarf companions (the Large and Small Magellanic Clouds), this is the closest known interacting dwarf-dwarf system where astronomers have directly observed both a gas bridge and resolved stellar populations. Together NGC 4490 and NGC 4485 form the system Arp 269, which is featured in the Atlas of Peculiar Galaxies. At such a close distance (and with Webb's impressive ability to peer through dusty cosmic clouds) these galaxies allow astronomers to witness up close the kinds of galaxy interactions that were common billions of years ago.

Dwarf galaxies likely share many similarities with young galaxies in the early Universe: they are much less massive than galaxies like the Milky Way, they typically have small amounts of metals (what astronomers call elements heavier than helium), and they contain a lot of gas and relatively few stars. When nearby dwarf galaxies collide, merge, or steal gas from one another, it can tell us how galaxies billions of years ago might have grown and evolved.

The nearby dwarf galaxies NGC 4490 and NGC 4485 form an intriguing pair. Nearly three decades ago, astronomers discovered a wispy bridge of gas connecting the two galaxies, showing that they have interacted in the past. Despite many studies with powerful telescopes like the Hubble Space Telescope, the history between NGC4490 and NGC 4485 has remained mysterious.

Recently, Webb observed this curious galactic pair as part of the Feedback in Emerging extrAgalactic Star clusTers (FEAST) programme (#1783; PI: A. Adamo). The FEAST programme used Webb's sensitive infrared eyes to reveal the formation of new stars in different types of nearby galaxies.

This image was developed using data from Webb's Near-InfraRed Camera (NIRCam) and Mid-InfraRed Instrument (MIRI), as well as a single narrow-band filter from Hubble (657N). It reveals NGC 4490 and NGC 4485 in never-before-seen detail and illuminates the bridge of gas and stars that connects them. NGC 4490 dominates the image as the larger object occupying the left side of the image, while NGC 4485 is the smaller galaxy that hosts the top-right portion of the image. By dissecting these galaxies star by star, researchers were able to map out where young, middle-aged, and old stars reside, and trace the timeline of the galaxies' interaction.

Roughly 200 million years ago, these galaxies whirled close to one another before waltzing away. The larger galaxy, NGC 4490, ensnared a stream of gas from its companion, and this gas now trails between the galaxies like dancers connected by outstretched arms. Along the newly formed bridge of gas and within the two galaxies, this interaction spurred a burst of new stars. The concentrated areas of bright blue that appear throughout the field indicate highly ionised regions of gas by the recently formed star clusters. Just 30 million years ago, these galaxies burst alight with stars once more, with new clusters coalescing where the gas of the two galaxies mixed together.

By capturing the history of the galactic dancers NGC 4490 and NGC 4485, Webb has revealed new details in how dwarf galaxies interact, giving us a glimpse of how small galaxies near and far grow and evolve.

Image Credit: ESA/Webb, NASA and CSA, A. Adamo (Stockholm University), G. Bortolini, and the FEAST JWST team

Image enhancement: Jean-Baptiste Faure

Interacting Galaxies Arp 107 as seen by Webb

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An interaction between an elliptical galaxy and a larger spiral galaxy, collectively known as Arp 107, seems to have given the spiral a happier outlook thanks to the two bright "eyes" and the wide semicircular "smile" that have resulted. This image is a composite, combining observations from Webb's MIRI (Mid-InfraRed Instrument) and NIRCam (Near-InfraRed Camera).

NIRCam highlights the stars within both galaxies and reveals the connection between them: a transparent, white bridge of stars pulled from both galaxies during their passage. MIRI data, represented in orange-red, show star-forming regions and dust that is composed of soot-like organic molecules known as polycyclic aromatic hydrocarbons. MIRI also provides a snapshot of the bright nucleus of the large spiral, home to a supermassive black hole.

The spiral galaxy is classified as a Seyfert galaxy, one of the two largest groups of active galaxies, along with galaxies that host quasars. Seyfert galaxies aren't as luminous or as distant as quasars, so they are better places to study similar phenomena in lower-energy light, like infrared.

This region is much like the Cartwheel Galaxy, one of the first interacting galaxies that Webb observed. Arp 107 may have turned out very similar in appearance to the Cartwheel, but since the smaller elliptical galaxy had an off-centre collision instead of a direct hit, the spiral galaxy got away with only its spiral arms being disturbed.

The collision isn't as bad as it sounds. Although there was much star formation occurring before, collisions between galaxies can compress gas, improving the conditions needed for more stars to form. On the other hand, as Webb reveals, collisions also disperse a lot of gas, potentially depriving new stars of the material they need to form.

Webb has captured these galaxies in the process of merging, which will take hundreds of millions of years. As the two galaxies rebuild after the chaos of their collision, Arp 107 may lose its smile, but it will inevitably turn into something just as interesting for future astronomers to study.

Arp 107 is located 465 million light-years from Earth in the constellation Leo Minor.

Image Credit: NASA, ESA, CSA, STScI

Image enhancement: Jean-Baptiste Faure

Interacting Galaxies Arp 142 as seen by Webb

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The distorted spiral galaxy at the center, the Penguin, and the compact elliptical galaxy at the left, the Egg, are locked in an active embrace. A new near- and mid-infrared image from the James Webb Space Telescope, taken to mark its second year of science, shows that their interaction is marked by a faint upside-down U-shaped blue glow.

The pair, known jointly as Arp 142, made their first pass between 25 and 75 million years ago – causing "fireworks", or new star formation, in the Penguin. In the most extreme cases, mergers can cause galaxies to form thousands of new stars per year for a few million years. For the Penguin, research has shown that about 100 to 200 stars have formed per year. By comparison, our Milky Way galaxy (which is not interacting with a galaxy of the same size) forms roughly six to seven new stars per year.

This gravitational shimmy also remade the Penguin's appearance. Its coiled spiral arms unwound, and gas and dust were pulled in an array of directions, like it was releasing confetti. It is rare for individual stars to collide when galaxies interact (space is vast), but the galaxies’ mingling disrupts their stars' orbits.

Today, the Penguin's galactic centre looks like an eye set within a head, and the galaxy has prominent star trails that take the shape of a beak, backbone, and fanned-out tail. A faint, but prominent dust lane extends from its beak down to its tail.

Despite the Penguin appearing far larger than the Egg, these galaxies have approximately the same mass. This is one reason why the smaller-looking Egg hasn't yet merged with the Penguin. (If one was less massive, it may have merged earlier.)

The oval Egg is filled with old stars, and little gas and dust, which is why it isn't sending out "streamers" or tidal tails of its own and instead has maintained a compact oval shape. If you look closely, the Egg has four prominent diffraction spikes – the galaxy's stars are so concentrated that it gleams.

Now, find the bright, edge-on galaxy at top right. It may look like a party crasher, but it's not nearby. Cataloged PGC 1237172, it lies 100 million light-years closer to Earth. It is relatively young and isn't overflowing with dust, which is why it practically disappears in Webb's mid-infrared view.

The background of this image is overflowing with far more distant galaxies. This is a testament to the sensitivity and resolution of Webb's infrared cameras.

Arp 142 lies 326 million light-years from Earth in the constellation Hydra.

Image Credit: NASA, ESA, CSA, STScI

Image enhancement: Jean-Baptiste Faure

Peculiar Galaxy NGC 7727

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Gemini South, one half of the International Gemini Observatory operated by NSF's NOIRLab, captured NGC 7727. This giant was born from the merger of two galaxies, an event that started around a billion years ago. At its center lies the closest pair of supermassive black holes ever found, two objects that are destined to coalesce into an even more massive black hole.

Just as you may bump into someone on a busy street, galaxies too can bump into each other. But while galactic interactions are much more violent than a bump on a busy street, individual stars don't generally collide since, compared to their sizes, the distances between them are very large. Rather, the galaxies dance around each other, with gravity creating tidal forces that dramatically change the look of the two dance partners. "Tails" of stars, gas and dust are spun around the galaxies as they eventually form a new, merged galaxy, resulting in the disordered and beautifully asymmetrical shape that we see in NGC 7727.

Also visible in this image are two bright points at the center of the galaxy, another telltale sign of its dramatic past. The core of NGC 7727 still consists of the original two galactic cores, each hosting a supermassive black hole. Located about 89 million light-years away from Earth, in the constellation of Aquarius, this is the closest pair of supermassive black holes to us.

The black holes in NGC 7727 are observed to be just 1600 light-years apart in the sky and are expected to merge within 250 million years, the blink of an eye in astronomical time. When the black holes merge they will create an even more massive black hole.

Our home galaxy, which also sports a supermassive black hole at its center, is on a path to merge with our closest large neighbour, the Andromeda Galaxy, billions of years from now. Perhaps the resulting galaxy will look something similar to the cosmic dance we see in NGC 7727, so this image could be giving us a glimpse into the future.

Image Credit: International Gemini Observatory/NOIRLab/NSF/AURA

Acknowledgment: PI: C. Onken (Australian National University)

Image processing: T.A. Rector (University of Alaska Anchorage/NSF's NOIRLab), J. Miller (International Gemini Observatory/NSF's NOIRLab), M. Rodriguez (International Gemini Observatory/NSF’s NOIRLab), M. Zamani (NSF's NOIRLab)

Image enhancement: Jean-Baptiste Faure

Peculiar Lenticular Galaxy NGC 2685

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The very unusual galaxy NGC 2685, also known as the Helix Galaxy, is located about 40 million light-years away in the constellation Ursa Major. This image was captured by the Gemini North telescope, one half of the International Gemini Observatory, operated by NSF NOIRLab which is funded by the U.S. National Science Foundation.

NGC 2685 is a peculiar lenticular galaxy known as a polar ring galaxy. A ring of gas, stars, and dust orbits NGC 2685 perpendicular to the flat plane of the host galaxy. This odd crossing of planes is believed to be evidence of galaxy interactions, mergers, or tidal accretion events. Current research suggests that the present structure of NGC 2685 was formed when it captured material from another galaxy, which was strung out into an encircling ring.

This galaxy is one of our closest known polar ring galaxies and is therefore one of the easiest of its kind to study. Owing to its odd characteristics, it has been called the most unusual galaxy in the Shapley-Ames Catalog of Bright Galaxies and appears as number 336 in astronomer Halton Arp's Atlas of Peculiar Galaxies.

Image Credit: International Gemini Observatory/NOIRLab/NSF/AURA/L. Bassino

Image processing: J. Miller (Gemini Observatory/NSF's NOIRLab), M. Rodriguez (Gemini Observatory/NSF's NOIRLab), and M. Zamani (NSF's NOIRLab)

Image enhancement: Jean-Baptiste Faure

Interacting Galaxies Arp 72

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This image features Arp 72, a very selective galaxy group that only includes two interacting galaxies: NGC 5996 (the large spiral galaxy) and NGC 5994 (its smaller companion, in the lower left of the image). Both galaxies lie approximately 160 million light-years from Earth, and their cores are separated from each other by a distance of around 67 thousand light-years. Moreover, the distance between the galaxies at their closest points is even smaller, closer to 40 thousand light-years. Whilst this might still sound vast, in galactic separation terms it is really very cosy! For comparison, the distance between the Milky Way and its nearest independent galactic neighbour Andromeda is around 2.5 million light-years. Alternatively, the distance between the Milky Way and its largest and brightest satellite galaxy, the Large Magellanic Cloud (satellite galaxies are galaxies that are bound in orbit around another galaxy), is about 162 thousand light-years.

Given this, coupled with the fact that NGC 5996 is roughly comparable in size to the Milky Way, it is not surprising that NGC 5996 and NGC 5994 – apparently separated by only 40 thousand light-years or so – are interacting with one another. In fact, the interaction might be what has caused the spiral shape of NGC 5996 to distort and apparently be drawn in the direction of NGC 5994. It also prompted the formation of the very long and faint tail of stars and gas curving away from NGC 5996, up to the top right of the image. This "tidal tail" is a common phenomenon that appears when galaxies get in close together, as can be seen in several Hubble images.

Image Credit: ESA/Hubble and NASA, L. Galbany, J. Dalcanton, Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA

Image enhancement: Jean-Baptiste Faure

Peculiar Galaxy Arp 122

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This Hubble picture 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 merging will not be a quick one either: it might take hundreds of millions of years to unfold. These collisions take so long because of the truly massive distances involved.

Galaxies are composed of stars and their solar systems, dust and gas. In galactic collisions, therefore, these constituent components may experience enormous changes in the gravitational forces acting on them. In time, this completely changes the structure of the two (or more) colliding galaxies, and sometimes ultimately results in a single, merged galaxy. That may well be what results from the collision pictured in this image. Galaxies that result from mergers are thought to have a regular or elliptical structure, as the merging process disrupts more complex structures (such as those observed in spiral galaxies). It would be fascinating to know what Arp 122 will look like once this collision is complete... but that will not happen for a long, long time.

Image Credit: ESA/Hubble and NASA, J. Dalcanton, Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA

Acknowledgement: L. Shatz

Image enhancement: Jean-Baptiste Faure

Interacting Galaxies Arp-Madore 2105-332

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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 Credit: ESA/Hubble and NASA, J. Dalcanton, Dark Energy Survey/DOE/FNAL/NOIRLab/NSF/AURA

Acknowledgement: L. Shatz

Image enhancement: Jean-Baptiste Faure

Interacting Galaxies Arp-Madore 2339-661

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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 Credit: ESA/Hubble and NASA, J. Dalcanton, Dark Energy Survey/DOE/FNAL/NOIRLab/NSF/AURA

Acknowledgement: L. Shatz

Image enhancement: Jean-Baptiste Faure

Interacting Galaxies Arp 107

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This Hubble picture taken using the 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.

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.

Image Credit: ESA/Hubble and NASA, J. Dalcanton

Image enhancement: Jean-Baptiste Faure

Intermediate Spiral Galaxy IC 5332

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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!

The galaxy glows brightly in the center and dims to cool colours towards the edge. Dark, faint filaments of dust and brightly glowing, pink and orange bubbles of star formation mark the face of the galaxy.

Image Credit: ESA/Hubble and NASA, R. Chandar, J. Lee and the PHANGS-HST team

Image enhancement: Jean-Baptiste Faure

Peculiar Spiral Galaxy ESO 415-19

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The peculiar spiral galaxy ESO 415-19, which lies around 450 million light-years away, stretches lazily across this image from the Hubble Space Telescope. While the center of this object resembles a regular spiral galaxy, long streams of stars stretch out from the galactic core like bizarrely elongated spiral arms. These are tidal streams caused by some chance interaction in the galaxy's past, and give ESO 415-19 a distinctly peculiar appearance.

ESO 415-19's peculiarity made it a great target for Hubble. This observation comes from an ongoing campaign to explore the Arp Atlas of Peculiar Galaxies, a menagerie of some of the weirdest and most wonderful galaxies that the Universe has to offer. These galaxies range from bizarre lonesome galaxies to spectacularly interacting galaxy pairs, triplets, and even quintets. These space oddities are spread throughout the night sky, which means that Hubble can spare a moment to observe them as it moves between other observational targets.

This particular observation lies in a part of the night sky contained by the Fornax constellation. This constellation was also the site of a particularly important Hubble observation; the Hubble Ultra Deep Field. Creating the Ultra Deep Field required almost a million seconds of Hubble time, and captured nearly 10,000 galaxies of various ages, sizes, shapes, and colours. Just as climate scientists can recreate the planet's atmospheric history from ice cores, astronomers can use deep field observations to explore slices of the Universe’s history from the present all the way to when the Universe was only 800 million years old!

Image Credit: ESA/Hubble and NASA, J. Dalcanton, Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA

Image enhancement: Jean-Baptiste Faure

Interacting Galaxies IC 1623 as pictured by Webb

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This image from the James Webb Space Telescope depicts IC 1623, an entwined pair of interacting galaxies which lies around 270 million light-years from Earth in the constellation Cetus. The two galaxies in IC 1623 are plunging headlong into one another in a process known as a galaxy merger. Their collision has ignited a frenzied spate of star formation known as a starburst, creating new stars at a rate more than twenty times that of the Milky Way galaxy.

This interacting galaxy system is particularly bright at infrared wavelengths, making it a perfect proving ground for Webb's ability to study luminous galaxies. A team of astronomers captured IC 1623 across the infrared portions of the electromagnetic spectrum using a trio of Webb's cutting-edge scientific instruments: MIRI, NIRSpec, and NIRCam. In so doing, they provided an abundance of data that will allow the astronomical community at large to fully explore how Webb's unprecedented capabilities will help to unravel the complex interactions in galactic ecosystems. These observations are also accompanied by data from other observatories, including the NASA/ESA Hubble Space Telescope, and will help set the stage for future observations of galactic systems with Webb.

The merger of these two galaxies has long been of interest to astronomers, and has previously been imaged by Hubble and by other space telescopes. The ongoing, extreme starburst causes intense infrared emission, and the merging galaxies may well be in the process of forming a supermassive black hole. A thick band of dust has blocked these valuable insights from the view of telescopes like Hubble. However, Webb's infrared sensitivity and its impressive resolution at those wavelengths allows it to see past the dust and has resulted in the spectacular image above, a combination of MIRI and NIRCam imagery.

The luminous core of the galaxy merger turns out to be both very bright and highly compact, so much so that Webb's diffraction spikes appear atop the galaxy in this image. The 8-pronged, snowflake-like diffraction spikes are created by the interaction of starlight with the physical structure of the telescope. The spiky quality of Webb's observations is particularly noticeable in images containing bright stars.

Image Credit: ESA/Webb, NASA and CSA, L. Armus & A. Evans

Acknowledgement: R. Colombari

Image enhancement: Jean-Baptiste Faure

The Cartwheel Galaxy as seen by Webb

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This image of the Cartwheel and its companion galaxies is a composite from Webb's Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI), which reveals details that are difficult to see in the individual images alone.

This galaxy formed as the result of a high-speed collision that occurred about 400 million years ago. The Cartwheel is composed of two rings, a bright inner ring and a colourful outer ring. Both rings expand outward from the centre of the collision like shockwaves.

However, despite the impact, much of the character of the large, spiral galaxy that existed before the collision remains, including its rotating arms. This leads to the “spokes” that inspired the name of the Cartwheel Galaxy, which are the bright red streaks seen between the inner and outer rings. These brilliant red hues, located not only throughout the Cartwheel, but also the companion spiral galaxy at the top left, are caused by glowing, hydrocarbon-rich dust.

In this near- and mid-infrared composite image, MIRI data are coloured red while NIRCam data are coloured blue, orange, and yellow. Amidst the red swirls of dust, there are many individual blue dots, which represent individual stars or pockets of star formation. NIRCam also defines the difference between the older star populations and dense dust in the core and the younger star populations outside of it.

Webb's observations capture Cartwheel in a very transitory stage. The form that the Cartwheel Galaxy will eventually take, given these two competing forces, is still a mystery. However, this snapshot provides perspective on what happened to the galaxy in the past and what it will do in the future.

Image Credit: NASA, ESA, CSA, STScI

Image enhancement: Jean-Baptiste Faure

Stephan's Quintet as seen by the Webb telescope

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An enormous mosaic of Stephan's Quintet is the largest image to date from NASA's James Webb Space Telescope, covering about one-fifth of the Moon's diameter. It contains over 150 million pixels and is constructed from almost 1,000 separate image files. The visual grouping of five galaxies was captured by Webb's Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI).

With its powerful, infrared vision and extremely high spatial resolution, Webb shows never-before-seen details in this galaxy group. Sparkling clusters of millions of young stars and starburst regions of fresh star birth grace the image. Sweeping tails of gas, dust and stars are being pulled from several of the galaxies due to gravitational interactions. Most dramatically, Webb's MIRI instrument captures huge shock waves as one of the galaxies, NGC 7318B, smashes through the cluster. These regions surrounding the central pair of galaxies are shown in the colors red and gold.

This composite NIRCam-MIRI image uses two of the three MIRI filters to best show and differentiate the hot dust and structure within the galaxy. MIRI sees a distinct difference in color between the dust in the galaxies versus the shock waves between the interacting galaxies. The image processing specialists at the Space Telescope Science Institute in Baltimore opted to highlight that difference by giving MIRI data the distinct yellow and orange colors, in contrast to the blue and white colors assigned to stars at NIRCam's wavelengths.  

Right: NIRCam image. Click the image for full resolution (172.05 MB)

Together, the five galaxies of Stephan's Quintet are also known as the Hickson Compact Group 92 (HCG 92). Although called a “quintet,” only four of the galaxies are truly close together and caught up in a cosmic dance. The fifth and leftmost galaxy, called NGC 7320, is well in the foreground compared with the other four. NGC 7320 resides 40 million light-years from Earth, while the other four galaxies (NGC 7317, NGC 7318A, NGC 7318B, and NGC 7319) are about 290 million light-years away. This is still fairly close in cosmic terms, compared with more distant galaxies billions of light-years away. Studying these relatively nearby galaxies helps scientists better understand structures seen in a much more distant universe.

This proximity provides astronomers a ringside seat for witnessing the merging of and interactions between galaxies that are so crucial to all of galaxy evolution. Rarely do scientists see in so much exquisite detail how interacting galaxies trigger star formation in each other, and how the gas in these galaxies is being disturbed. Stephan’s Quintet is a fantastic “laboratory” for studying these processes fundamental to all galaxies.

Tight groups like this may have been more common in the early universe when their superheated, infalling material may have fueled very energetic black holes called quasars. Even today, the topmost galaxy in the group – NGC 7319 – harbors an active galactic nucleus, a supermassive black hole that is actively accreting material.

In NGC 7320, the leftmost and closest galaxy in the visual grouping, NIRCam was remarkably able to resolve individual stars and even the galaxy's bright core. Old, dying stars that are producing dust clearly stand out as red points with NIRCam.

The new information from Webb provides invaluable insights into how galactic interactions may have driven galaxy evolution in the early universe. As a bonus, NIRCam and MIRI revealed a vast sea of many thousands of distant background galaxies reminiscent of Hubble's Deep Fields.

Image Credit: NASA, ESA, CSA, and STScI

Image enhancement: Jean-Baptiste Faure

Interacting Galaxies NGC 7764A

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The subject of this image is a group of three galaxies, collectively known as NGC 7764A. They were imaged by the Hubble Space Telescope, using both its Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3). The two galaxies in the upper right of the image appear to be interacting with one another – indeed, the long trails of stars and gas extending from them both give the impression that they have both just been struck at great speed, thrown into disarray by the bowling-ball-shaped galaxy to the lower left of the image. In reality, however, interactions between galaxies happen over very long time periods, and galaxies rarely collide head-on with one another. It is also unclear whether the galaxy to the lower left is actually interacting with the other two, although they are so relatively close in space that it seems possible that they are. By happy coincidence, the collective interaction between these galaxies have caused the two on the upper right to form a shape, which from our Solar System's perspective, ressembles the starship known as the USS Enterprise from Star Trek!

NGC 7764A, which lies about 425 million light years from Earth in the constellation Phoenix, is a fascinating example of just how awkward astronomical nomenclature can be. The three galaxies are individually referred to as NGC 7764A1, NGC 7764A2 and NGC 7764A3, and just to be really difficult, an entirely separate galaxy, named NGC 7764, sits in the skies about a Moon's distance (as seen from Earth) away. This rather haphazard naming makes more sense when we consider that many of the catalogues for keeping track of celestial bodies were compiled well over 100 years ago, long before modern technology made standardising scientific terminology much easier. As it is, many astronomical objects have several different names, or might have names that are so similar to other objects' names that they cause confusion.

Image Credit: ESA/Hubble and NASA, J. Dalcanton, Dark Energy Survey, DOE, FNAL, DECam, CTIO, NOIRLab/NSF/AURA, ESO

Acknowledgement: J. Schmidt

Image enhancement: Jean-Baptiste Faure

Interacting Galaxies Arp 86

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This picture from the Hubble Space Telescope showcases Arp 86, a peculiar pair of interacting galaxies which lies roughly 220 million light-years from Earth in the constellation Pegasus. Arp 86 is composed of the two galaxies NGC 7752 and NGC 7753 – NGC 7753 is the large spiral galaxy dominating this image, and NGC 7752 is its smaller companion. The diminutive companion galaxy almost appears to be attached to NGC 7753, and it is this peculiarity that has earned the designation “Arp 86” – signifying that the galaxy pair appears in the Atlas of Peculiar Galaxies compiled by the astronomer Halton Arp in 1966. The gravitational squabble between the two galaxies is doomed to end catastrophically for NGC 7752. It will eventually either be flung out into intergalactic space or be entirely engulfed by its far larger neighbour.

Hubble observed Arp 86 as part of a larger effort to understand the connections between young stars and the clouds of cold gas in which they form. Hubble gazed into star clusters and clouds of gas and dust in a variety of environments dotted throughout nearby galaxies. Combined with measurements from ALMA, a gigantic radio telescope perched high in the Chilean Andes, these Hubble observations provide a treasure trove of data for astronomers working to understand how stars are born.

These observations also helped sow the seeds of future research with an upcoming space telescope, the NASA/ESA James Webb Space Telescope (JWST). This telescope, due to launch later this year, will study star formation in dusty regions such as the galaxies of Arp 86.

Image Credit: ESA/Hubble and NASA, Dark Energy Survey, J. Dalcanton

Image enhancement: Jean-Baptiste Faure

Interacting Galaxies Arp 91

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This picture features two interacting galaxies that are so intertwined, they have a collective name – Arp 91. This delicate galactic dance is taking place over 100 million light-years from Earth, and was captured by the Hubble Space Telescope. The two galaxies comprising Arp 91 do have their own names: the lower galaxy, which in this image looks like a bright spot, is known as NGC 5953; and the ovoid galaxy to the upper right is NGC 5954. In reality, both of these galaxies are spiral galaxies, but their shapes appear very different because they are orientated differently with respect to Earth.

Arp 91 provides a particularly vivid example of galactic interaction. NGC 5954 is clearly being tugged towards NGC 5953 – it looks like it is extending one spiral arm downwards. It is the immense gravitational attraction of the two galaxies that is causing them to interact. Such gravitational interactions between galaxies are common, and are an important part of galactic evolution. Most astronomers nowadays believe that collisions between spiral galaxies lead to the formation of another type of galaxy, known as elliptical galaxies. These immensely energetic and massive collisions, however, happen on timescales that dwarf a human lifetime – they take place over hundreds of millions of years. So we should not expect Arp 91 to look any different over the course of our lifetimes!

Image Credit: ESA/Hubble and NASA, J. Dalcanton

Acknowledgement: J. Schmidt

Image enhancement: Jean-Baptiste Faure

Interacting Galaxies Arp 195

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A dramatic triplet of galaxies takes center stage in this latest Picture of the Week from the Hubble Space Telescope, which captures a three-way gravitational tug-of-war between interacting galaxies. This system – known as Arp 195 – is featured in the Atlas of Peculiar Galaxies, a list which showcases some of the weirder and more wonderful galaxies in the universe.

Observing time with the Hubble Space Telescope is extremely valuable, so astronomers don't want to waste a second. The schedule for Hubble observations is calculated using a computer algorithm which allows the spacecraft to occasionally gather bonus snapshots of data between longer observations. This image of the clashing triplet of galaxies in Arp 195 is one such snapshot. Extra observations such as these do more than provide spectacular images – they also help to identify promising targets to follow up with telescopes such as the upcoming NASA/ESA/CSA James Webb Space Telescope.

Image Credit: ESA/Hubble and NASA, J. Dalcanton

Image enhancement: Jean-Baptiste Faure