Galaxy Cluster MACS J0553.4-3342 by Webb

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In this picture from the James Webb Space Telescope we are taken on a visit to a building site of significant scale. The project is a galaxy cluster named MACS J0553.4-3342, located in the constellation Columba (the Dove).

MACS J0553.4-3342 is situated at a redshift of 0.412. Redshift is a measure of how much the cluster's light has been stretched by the expansion of the Universe over the course of its long journey to Webb's mirrors; this unassuming number tells us that we are seeing MACS J0553.4-3342 as it was 4.4 billion years in the past. But for a galaxy cluster, this is relatively young. In fact, observations with the Hubble Space Telescope and other telescopes show a cluster still in the process of being built.

MACS J0553.4-3342 is composed of two sub-clusters – roughly equal in mass – that are actively merging. The two subclusters have already slammed through each other and travelled over one million light-years apart, but they will eventually come back together again and again until they finally merge. The construction process is messy, and MACS J0553.4-3342 is filled with extremely hot gas that radiates powerful X-rays. Each subcluster is anchored on an immensely bright and massive elliptical galaxy, which are easily identifiable as the two brightest points in the centre of this scene with the largest glowing halos around them. The many smaller white elliptical galaxies are bound to one of the two subclusters by gravity, and will be incorporated into the final galaxy cluster. This image also features many foreground galaxies – spirals and dusty discs that are unrelated to MACS J0553.4-3342 – and prominent bright stars in our own Milky Way galaxy.

Even mid-way through its construction, the titanic clumps of matter swirling around in this galaxy cluster have built a device that is already very useful for us here on Earth: a gravitational lens. The extreme and concentrated mass in MACS J0553.4-3342 curves light with its gravity, similar to how a glass lens bends and focuses light. In this image you can see prominent orange, stretched-out arcs alongside each of the subclusters. These arcs are images of distant background galaxies, whose light has been warped by the galaxy cluster's gravitational pull. The arc on the left side, three bright spots joined together, is actually three images of a single background galaxy! A forest of smaller arcs and lines are scattered across the image too; such a fantastic view appears in few other places in the Universe.

Look in the right spot, however, and this galaxy cluster turns from a distorting funhouse mirror into a precision scientific device. The gravitational lensing focuses light, magnifying objects and enhancing their brightness so if they lie in exactly the right place, background galaxies and even individual stars that would have been far too faint and distant to spot will be made visible. By carefully mapping out the mass of the cluster, researchers can reconstruct where and how strongly it distorts light from our point of view, then search for serendipitously-magnified distant objects to study. The arcs we can see in MACS J0553.4-3342 already show a few galaxies from less than a billion years after the Big Bang.

This image, taken with Webb's Near-Infrared Camera (NIRCam), stems from a survey programme named VENUS (#6882). Astronomers aimed to create a collection of deep, high-quality images of massive galaxy clusters like MACS J0553.4-3342 across a wide range of infrared wavelengths, greatly expanding the area covered by Webb's sensitive instruments. Researchers can then scour the clusters for distant and faint objects that have been brightened through gravitational lensing, from young galaxies and low-mass black holes to supernova explosions and individual stars. Gravitational lensing has been key to many of Webb's most dramatic discoveries in recent years, and having many more examples of it allows us to systematically study the distant past and the evolutionary stages of the galaxies, stars and black holes we see today.

Image Credit: ESA/Webb, NASA and CSA, S. Fujimoto

Image enhancement: Jean-Baptiste Faure

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

Globular Cluster NGC 6723

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The subject of this picture is an ancient inhabitant of our galaxy. This sparkling scene is of a globular cluster: a collection of tens of thousands to millions of stars, all tightly bound together under the influence of gravity. Astronomers know of more than 150 globular clusters in our galaxy, though there may be others yet to be discovered, hidden from view by dust or densely packed fields of stars.

This particular globular cluster is NGC 6723, sometimes called the Chandelier Cluster. Much like its namesake, this cluster sparkles with countless lights – but each "lightbulb" in this chandelier is an individual star 27 000 light-years away in the constellation Sagittarius (the Archer).

Globular clusters like NGC 6723 contain some of the oldest stars in our galaxy. The ages of these clusters often exceed 10 billion years old, and some are nearly as old as the Universe itself. Globular clusters are thought to be some of the first structures to have formed in our galaxy, coalescing potentially billions of years before the thin disk of stars in which our Sun orbits. The details of how globular clusters formed, however, are not yet certain.

Astronomers initially thought that all stars in a globular cluster formed at the same time in a single flourish of star formation. This would mean that all stars in a globular cluster would be the same age and be made of the same mixture of chemical elements. Now, thanks to observations from telescopes like Hubble, researchers know that these seemingly simple stellar populations have more complex histories than originally thought.

Hubble first observed NGC 6723 as part of an ambitious survey dedicated to demystifying the properties of globular clusters in our Milky Way galaxy. In this observing programme, researchers used Hubble to study 65 globular clusters in our galaxy in visible and near-infrared light. These data allowed researchers to study everything from the ages of globular clusters to the process through which massive stars sink to the centre of a star cluster and lower-mass stars drift toward the cluster outskirts. This survey has been immensely scientifically valuable, and these observations have inspired several hundred published research papers.

In a later observing programme, researchers set their sights again on many of these same clusters, including NGC 6723. This time, they used Hubble's unique sensitivity to ultraviolet light to detect the subtle variations in chemical composition between the stars of globular clusters and determine the age spread among the clusters' stars. For NGC 6723, researchers found evidence of two closely-spaced periods of star formation, the second occurring within 634 million years of the first. "Closely-spaced" is relative; 634 million years is a blink of an eye for a star cluster that is more than 10 billion years old!

Thanks to these findings, astronomers are on the path to understanding how and when globular clusters formed – and Hubble observations of celestial chandeliers like NGC 6723 are lighting the way.

Image Credit: ESA/Hubble and NASA, A. Sarajedini, G. Piotto

Image enhancement: Jean-Baptiste Faure

Star-Forming Region N11 in the LMC

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This Hubble Space Telescope picture features a cloudy starscape from an impressive star cluster. This scene is located in the Large Magellanic Cloud, a dwarf galaxy situated about 160 000 light-years away in the constellations Dorado and Mensa. With a mass equal to 10–20% of the mass of the Milky Way, the Large Magellanic Cloud is the largest of the dozens of small galaxies that orbit our galaxy.

The Large Magellanic Cloud is home to several massive stellar nurseries where gas clouds, like those strewn across this image, coalesce into new stars. This image depicts a portion of the galaxy's second-largest star-forming region, which is called N11. (The most massive and prolific star-forming region in the Large Magellanic Cloud, the Tarantula Nebula, is a frequent target for Hubble.) We see bright, young stars lighting up the gas clouds and sculpting clumps of dust with powerful ultraviolet radiation.

This image marries observations made roughly 20 years apart, a testament to Hubble's longevity. The first set of observations, which were carried out in 2002–2003, capitalised on the exquisite sensitivity and resolution of the then-newly-installed Advanced Camera for Surveys. Astronomers turned Hubble toward the N11 star cluster to do something that had never been done before at the time: catalogue all the stars in a young cluster with masses between 10% of the Sun's mass and 100 times the Sun's mass.

The second set of observations came from Hubble's newest camera, the Wide Field Camera 3. These images focused on the dusty clouds that suffuse the cluster, bringing a new perspective on cosmic dust.

Image Credit: ESA/Hubble and NASA, C. Murray, J. Maíz Apellániz

Image enhancement: Jean-Baptiste Faure

Intermediate Spiral Galaxy NGC 3137

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In this Hubble picture, a spiral galaxy glittering with star clusters is the center of attention. NGC 3137 is located 53 million light-years away in the constellation Antlia (The Air Pump). As a nearby spiral galaxy, this target offers astronomers an excellent opportunity to study the cycle of stellar birth and death, as well as giving researchers a glimpse of a galactic system similar to our own.

NGC 3137 is of particular interest to astronomers because it travels through space with a group of galaxies that is thought to be similar to the Local Group, the galaxy group that contains the Milky Way. Similar to the Local Group, the NGC 3175 group contains two large spiral galaxies: NGC 3137 and NGC 3175, which Hubble has also observed. In the Local Group, the largest members are the Milky Way galaxy and Andromeda, another spiral galaxy. In addition to two large spiral galaxies, both groups also contain a number of smaller dwarf galaxies, although it's not yet known how many of these tiny companions the NGC 3175 group has; researchers have found more than 500 dwarf galaxy candidates. By studying this nearby galaxy group, astronomers can learn about the dynamics of our own galactic home.

NGC 3137 is revealed in fantastic detail by Hubble. This image is crafted from observations in six different colour bands, creating a view that highlights several facets of this beautiful spiral. The galaxy's center, which is encircled by a network of fine, dusty clouds, hosts a black hole estimated to be 60 million times more massive than the Sun. NGC 3137 is highly inclined from our point of view, giving a unique perspective on its loose, feathery spiral structure. A couple of photobombing Milky Way stars and a smattering of far more distant background galaxies complete the image.

As stunning as each of these features may be, it's the galaxy's brilliant star clusters that steal the show. The galaxy is peppered with dense clusters of bright blue stars and glowing red gas clouds, which signal the presence of hot, young stars still encased in their birth nebulae.

Unsurprisingly, these star clusters are exactly what has drawn Hubble's keen eye. Researchers are using Hubble to carry out an observing programme focusing on star clusters in 55 nearby galaxies. The data collected will help astronomers identify star clusters and the glowing nebulae that surround them, providing a way to measure the ages of stars in galaxies like NGC 3137. These observations give an in-depth view of stellar life in spiral galaxies, from the young stars still in the process of forming to the ancient stellar populations that grew up in the early years of their galactic hosts.

The PHANGS-HST programme for which these observations were taken is part of a larger effort by some of the most powerful observatories on (and around) Earth. Hubble contributes greatly to this massive undertaking, which combines data from the James Webb Space Telescope and the Atacama Large Millimetre/submillimetre Array (ALMA). Together, Hubble's powerful optical and ultraviolet capabilities, Webb's sensitive infrared eyes, and ALMA's broad network of radio dishes bring us an unmatched view of star formation in the local Universe.

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

Image enhancement: Jean-Baptiste Faure

Lasers projected from the 4LGSF on VLT-UT4

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This photo is a majestic portrait of UT4, one of the four 8-m telescopes of ESO's Very Large Telescope (VLT). Framed against the star-filled sky of the Paranal Observatory, this telescope is much more than a passive observer. From within its dome, it pierces the peaceful night with four laser beams.

These lasers are projected from the 4 Laser Guide Star Facility (4LGSF), which UT4 uses to create its own artificial stars in the sky. The lasers create these points of light by exciting sodium atoms in the atmosphere, about 90 km above the ground, causing them to glow. These "stars" then act as guides, and by studying how they are blurred by the atmosphere the telescope learns how to adjust for atmospheric turbulence – the same turbulence that makes every little star twinkle.

The adjustments are made by UT4's adaptive optics system, which can precisely deform the telescope's secondary mirror to cancel out atmospheric disturbances measured by the system. Using adaptive optics, a ground-based telescope can take much sharper images than the atmosphere would normally allow – it's almost as good as sending the VLT up into space.

Soon, the other three 8-m telescopes of the VLT will be equipped with one laser each. This is part of a series of upgrades of the VLT Interferometer and its GRAVITY+ instrument, which can combine the light of several telescopes to create a huge "virtual" telescope. Another massive eye on the sky, ESO's Extremely Large Telescope (ELT), is nearing completion not far from Paranal, and will be equipped with at least 6 lasers, to deliver the sharpest images possible with a ground-based telescope.

Image Credit: ESO/A. de Burgos Sierra

Galaxy Cluster MACS J1149.5+2223 by Webb

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This James Webb Space Telescope picture brings us a scene from the distant Universe. Pictured here is the galaxy cluster MACS J1149.5+2223, or MACS J1149 for short, which is located about 5 billion light-years away in the constellation Leo.

Galaxy clusters are the largest structures in the Universe that are held together by gravity. Astronomers have confirmed more than 300 galaxies belonging to the MACS J1149 cluster, and they've identified several hundred more possible members. At the cluster's center, a huddle of ghostly elliptical galaxies rules over the cluster with their immense gravity.

The crushing gravity of this cluster does more than just hold all the galaxies together as they drift through space. As light from galaxies located behind the cluster makes its way toward our telescope, journeying for billions of years, its path through spacetime is bent by the mass of the intervening galaxies.

This phenomenon is called gravitational lensing, and the result is evident in this image of MACS J1149; scattered across the image are subtle and not-so-subtle examples of gravitational lensing, from galaxies that appear to have been stretched into narrow streaks of light to galaxy images that have morphed into strange shapes.

A fantastic example of gravitational lensing can be seen near the centre of the image, just below the brilliant white galaxies at the heart of the cluster. There, the image of a galaxy with distinct spiral arms has been stretched into something resembling a pink jellyfish. This tangled-looking galaxy is home to what was once the most distant single star ever discovered as well as a supernova whose image appeared four times at once.

MACS J1149 has long received the celebrity treatment from leading telescopes, and for good reason. This cluster was one of six investigated through the Hubble Space Telescope's Frontier Fields programme. The Frontier Fields galaxy clusters were selected for the strength of their gravitational lensing, and their ability to warp spacetime has granted researchers a glimpse into the early Universe.

Now, Webb is pushing our knowledge horizon to even earlier times, enabling new discoveries like a feasting supermassive black hole less than 600 million years after the Big Bang. Using Webb's Near-Infrared Spectrograph (NIRSpec), Near-InfraRed Camera (NIRCam), and Near-InfraRed Imager and Slitless Spectrograph (NIRISS), researchers are revealing never-before-seen details of the lives of early galaxies.

The Webb data used to create this image were collected as part of the CAnadian NIRISS Unbiased Cluster Survey (CANUCS) programme #1208. This programme uses Webb's sensitive instruments to unveil the evolution of low-mass galaxies in the early Universe, revealing their star formation, dust and chemistry. These data will also help researchers study the epoch of reionisation, when the first stars and galaxies lit up the Universe, map the distribution of mass within galaxy clusters, and understand how star formation can slow to a trickle in a cluster environment.

Image Credit: ESA/Webb, NASA and CSA, C. Willott (National Research Council Canada), R. Tripodi (INAF - Astronomical Observatory of Rome)

Image enhancement: Jean-Baptiste Faure