Barred Spiral Galaxy NGC 1672

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This Hubble picture features NGC 1672, a barred spiral galaxy located 49 million light-years from Earth in the constellation Dorado. This galaxy is a multi-talented light show, showing off an impressive array of different celestial lights. Like any spiral galaxy, its disc is filled with billions of shining stars that give it a beautiful glow. Along its two large arms, bubbles of hydrogen gas are made to shine a striking red light by the powerful radiation of newly-forming stars within. Near to the centre lie some particularly spectacular stars; newly-formed and extremely hot, they are embedded in a ring of hot gas and are emitting powerful X-rays. And in the very centre sits an even more brilliant source of X-rays, an active galactic nucleus created by the heated accretion disc around NGC 1672's supermassive black hole; this makes NGC 1672 a Seyfert galaxy.

But a highlight of this image is the most fleeting and temporary of these lights: supernova SN 2017GAX, visible in just one of the six Hubble images that make up this composite image. This was a Type I supernova caused by the core-collapse and subsequent explosion of a giant star, going from invisibility to a new light in the sky in just a matter of days. In that image from later that year, the supernova is already fading, and so is only just visible here as a small green dot, just below the crook of the spiral arm on the right side. In fact this was on purpose, as astronomers wanted to look for any companion star that the supernova progenitor may have had – something impossible to spot beside a live supernova! For a closer look at the supernova's appearance, you can compare the two images with this slider tool.

Image Credit: ESA/Hubble and NASA, O. Fox, L. Jenkins, S. Van Dyk, A. Filippenko, J. Lee and the PHANGS-HST Team, D. de Martin (ESA/Hubble), M. Zamani (ESA/Hubble)

Image enhancement: Jean-Baptiste Faure

Intermediate Spiral Galaxy M90 (NGC 4569)

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The striking spiral galaxy featured in this picture of the Week is M90 (Messier 90, also NGC 4569), located in the constellation Virgo. In 2019, an image of M90 was released using data from the older Wide Field and Planetary Camera 2 – data taken in 1994 soon after the camera's installation. That image has a distinctive stair-step pattern due to the layout of WFPC2's sensors. WFPC2 was replaced in 2010 by the Wide Field Camera 3, and Hubble used WFC3 when it turned its aperture to Messier 90 again in 2019 and 2023. The resulting data was processed to create this stunning new image, providing a much fuller view of the galaxy's dusty disc, its gaseous halo and its bright core.

The inner regions of M90's disc are sites of star formation, which is highlighted here by red H-alpha light from nebulae, but this is absent in the rest of the galaxy. M90 sits among the galaxies of the relatively nearby Virgo Cluster, and the course of its orbit took it on a path near the cluster's center about three hundred million years ago. The density of gas in the inner cluster weighed on M90 like a strong headwind, stripping enormous quantities of gas from the galaxy and creating the diffuse halo that can be seen around it here. This gas is no longer available for M90 to form new stars with, and it will eventually fade as a spiral galaxy as a result.

M90 is located 55 million light-years from Earth, but it's one of the very few galaxies getting closer to us. Its orbit through the Virgo cluster has accelerated it so much that it’s in the process of escaping the cluster entirely, and by happenstance it's moving in our direction – other galaxies in the Virgo cluster have been measured at similar speeds, but in the opposite direction. Over the coming billions of years, we will be treated to a yet better view of M90 while it evolves into a lenticular galaxy.

Image Credit: ESA/Hubble and NASA, D. Thilker, J. Lee and the PHANGS-HST Team

Image enhancement: Jean-Baptiste Faure

Emission Nebula and Open Cluster IC 2948

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Exploring the gas cloud known as IC 2948 means finding your way across countless nascent stars born in this enormous stellar nursery. And yet, this is just a snippet of a much larger object: the Running Chicken Nebula. This nebula spans an area on the night sky close to 25 full moons, and yet, the area you see here is not even a third of a full moon. Obtaining such a detailed snippet of the nebula was possible thanks to a 1.5-billion-pixel image taken by the VLT Survey Telescope (VST), hosted and operated by ESO.

Located in the constellation of the Centaur (Centaurus), the Running Chicken Nebula is a labyrinth of gas, dust and young stars whose highly intense radiation erodes away the surrounding material. The gas cloud IC 2948 is the brightest region of the nebula. Here, we find creeping dark clouds, shaped like open hands about to grab their surrounding blooming stars.

First discovered more than a century ago, this gas cloud is helping us understand how stars form and behave during their infancy. To spot IC 2948 within the much larger Running Chicken Nebula, locate the chicken’s rear end (or its head, as some people claim). In your search, you may come across other areas like the stunning GUM 41 nebula.

Image Credit: ESO/VPHAS+ team. Acknowledgement: CASU

Image enhancement: Jean-Baptiste Faure

Intermediate Spiral Galaxy NGC 5248

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The sparkling scene depicted in this Hubble picture is of the spiral galaxy NGC 5248, located 42 million light-years from Earth in the constellation Boötes. It is also known as Caldwell 45, having been included in a catalogue of visually interesting celestial objects that were known, but weren't as commonly observed by amateur astronomers as the more famous Messier objects.

NGC 5248 is one of the so-called "grand design" spirals, with prominent spiral arms that reach from near the core out through the disc. It also has a faint bar structure in the center, between the inner ends of the spiral arms, which is not quite so obvious in this visible-light portrait from Hubble. Features like these which break the rotational symmetry of a galaxy have a huge influence on how matter moves through it, and eventually its evolution through time. They feed gas from a galaxy's outer reaches to inner star-forming regions, and even to a galaxy's central black hole where it can kick-start an active galactic nucleus.

These flows of gas have shaped NGC 5248 in a big way; it has many bright "starburst regions" of intense star formation spread across its disc, and it is dominated by a population of young stars. The galaxy even has two very active, ring-shaped starburst regions around its nucleus, filled with young clusters of stars. These "nuclear rings" are remarkable enough, but normally a nuclear ring tends to block gas from getting further into the core of a galaxy. NGC 5248 having a second ring inside the first is a marker of just how forceful its flows of matter and energy are! Its relatively nearby, highly visible starburst regions make the galaxy a target for professional and amateur astronomers alike.

Image Credit: ESA/Hubble and NASA, F. Belfiore, J. Lee and the PHANGS-HST Team

Image enhancement: Jean-Baptiste Faure

Rosette Nebula NGC 2237 and Open Cluster NGC 2244

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Cradled within the fiery petals of the Rosette Nebula (NGC 2237) is NGC 2244, the young star cluster which it nurtured. The cluster's stars light up the nebula in vibrant hues of red, gold and purple, and opaque towers of dust rise from the billowing clouds around its excavated core. This image, captured by 570-megapixel Department of Energy-fabricated Dark Energy Camera (DECam), mounted on the U.S. National Science Foundation Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory, a Program of NSF NOIRLab, is being released in celebration of NOIRLab's fifth anniversary.

Image Credit: CTIO/NOIRLab/DOE/NSF/AURA

Image Processing: T.A. Rector (University of Alaska Anchorage/NSF NOIRLab), D. de Martin and M. Zamani (NSF NOIRLab)

Open Cluster Westerlund 1 as seen by Webb

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The open cluster Westerlund 1, showcased in this new Webb picture, is located roughly 12 000 light-years away in the southern constellation Ara (the Altar) where it resides behind a huge interstellar cloud of gas and dust. It was discovered in 1961 from Australia by Swedish astronomer Bengt Westerlund. Westerlund 1 is an incomparable natural laboratory for the study of extreme stellar physics, helping astronomers to find out how the most massive stars in our Galaxy live and die.

The unique draw of Westerlund 1 is its large, dense, and diverse population of massive stars, which has no counterpart in other known Milky Way galaxy clusters in terms of the number of stars and the richness of spectral types and evolutionary phases. All stars identified in this cluster are evolved and very massive, spanning the full range of stellar classifications including Wolf-Rayet stars, OB supergiants, yellow hypergiants (nearly as bright as a million Suns) and luminous blue variables. Because such stars have a rather short life, Westerlund 1 is very young, astronomically speaking. Astronomers estimate the cluster's age to be somewhere between 3.5 and 5 million years (its exact age is still a matter of debate), making it a newborn cluster in our galaxy. In the future, it is believed that it will likely evolve from an open cluster into a globular cluster. These are roughly spherical, tightly packed collections of old stars bound together by gravity.

Currently, only a handful of stars form in our galaxy each year, but in the past the situation was different. The Milky Way galaxy used to produce many more stars, likely hitting its peak of churning out dozens or hundreds of stars per year about 10 billion years ago and then gradually declining ever since. Astronomers think that most of this star formation took place in massive clusters of stars, known as "super star clusters". These are young clusters of stars that contain more than 10,000 times the mass of the Sun, packed into an unbelievably small volume. They represent the most extreme environments in which stars and planets can form. Only a few super star clusters still exist in our galaxy – of which Westerlund 1 is one – but they offer important clues about this earlier era when most of our galaxy's stars formed.

Westerlund 1 is an impressive example of a super star cluster: it contains hundreds of very massive stars, some shining with a brilliance of almost one million Suns and others two thousand times larger than the Sun (as large as the orbit of Saturn). Indeed, if the Solar System was located at the heart of this remarkable cluster, our sky would be full of hundreds of stars as bright as the full Moon. It appears to be the most massive compact young cluster yet identified in the Milky Way galaxy: astronomers believe that this extreme cluster contains between 50 000 and 100 000 times the mass of the Sun, yet all of its stars are located within a region less than six light-years across. Even so, it is the biggest of these remaining super star clusters in the Milky Way galaxy, and the closest super star cluster to Earth. These qualities make Westerlund 1 an excellent target for studying the impact of a super star cluster's environment on the formation process of stars and planets, as well as the evolution of stars over a broad range of masses.

The huge population of massive stars in Westerlund 1 suggests that it will have a very significant impact on its surroundings. The cluster contains so many massive stars that in a time span of less than 40 million years, it will be the site of more than 1 500 supernovae. This super star cluster now provides astronomers with a unique perspective towards one of the most extreme environments in the Universe. Westerlund 1 will certainly provide new opportunities in the long-standing quest for more and finer details about how stars, and especially massive stars, form.

This image was captured as part of the The Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) with Webb's Near-InfraRed Camera (NIRCam). This survey is a dedicated Webb program (GO 1905, PI: M. G. Guarcello) that aims to study star and planet formation and stellar evolution in starburst regions in Westerlund 1 and Westerlund 2, two of the closest super star clusters to the Sun.

With its unparalleled performance in the infrared, Webb offers astronomers the opportunity to unveil the population of low-mass stars in local super star clusters for the first time, and to study the environments around these clusters' most massive stars. Webb observations of the massive stars in super star clusters can shed light on how feedback (stellar winds, supernovae and other ejected material) from these stars impacts their surrounding environments and the overall star formation process within their parental clouds.

Image Credit: ESA/Webb, NASA and CSA, M. Zamani (ESA/Webb), M. G. Guarcello (INAF-OAPA) and the EWOCS 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