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

Open Cluster Bochum 14 as imaged by Rubin

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This image shows the open star cluster Bochum 14, captured by the NSF–DOE Vera C. Rubin Observatory. Open clusters like this are made up of stars that formed together from the same cloud of gas and dust, remaining loosely bound as they drift through the Milky Way. Observations like this help astronomers study how stars are born, evolve, and spread out over time. With its powerful wide-field view, the Rubin Observatory is set to reveal countless scenes like this across the southern sky.

Image Credit: RubinObs/NOIRLab/SLAC/NSF/DOE/AURA

Image enhancement: Jean-Baptiste Faure

The Virgo Cluster deeply imaged by Rubin

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Introducing the first riches from NSF–DOE Vera C. Rubin Observatory's cosmic treasure chest, a wealth of data that will help scientists make countless new discoveries about our Universe. This image exposes a Universe teeming with stars and galaxies – transforming seemingly empty, inky-black pockets of space into glittering tapestries for the first time. Only Rubin can quickly produce such large images with this much color and richness. Here, Rubin's view is focused on the southern region of the Virgo Cluster, about 55 million light-years away from Earth and the nearest large collection of galaxies to our own Milky Way.

The image offers a stunning variety of objects – from bright stars ranging from blue to red in color, to nearby blue spiral galaxies, to distant red galaxy groups – demonstrating the broad range of science made possible by Rubin data. During the 10-year Legacy Survey of Space and Time, scientists around the world will access Rubin’s treasure trove of data to address questions like: How did the Milky Way form? What makes up the 95% of the Universe we can’t see? What will a detailed inventory of Solar System objects reveal? What will we learn from watching hundreds of millions of changes in the night sky over 10 years?

Apart from a few foreground stars in our own Milky Way, the myriad specks of light captured here make up a rich tapestry of about 10 million galaxies – just 0.05% of the roughly 20 billion galaxies Rubin will image during its 10-year Legacy Survey of Space and Time (LSST). By the end of the survey, Rubin will have revealed this level of detail across the entire southern sky.

In addition to showcasing the richness and variety of celestial light in (this area), this deep, 15-square-degree image provides a sample of the way Rubin will observe during the main survey. Each individual exposure taken by Rubin Observatory covers 10 square degrees, (about 45 full moons). Combining multiple exposures of the same place on the sky – taken at different times and with different color filters – reveals extremely faint details that wouldn't be captured in a single exposure. The 1185 exposures combined to make this image were taken over a period of just 7 nights. Rubin Observatory is the only astronomical tool in existence that can assemble an image this wide and deep so quickly.

The bright stars scattered throughout this image belong to our home galaxy. By tracking their positions, brightness, and for some, even their motion over time, Rubin will help map the Milky Way in extraordinary detail – revealing its structure, history, and how it has evolved over time. With observations of never-before-seen stellar streams, dwarf galaxies, and more, Rubin data will help scientists investigate the dynamic past of our cosmic neighborhood.

In Rubin Observatory's Skyviewer tool, you can use the "display" setting to toggle between a view with and without asteroids, which appear as multicolored streaks. These moving asteroids in our Solar System were captured by Rubin's fast system at a different location in each exposure, and this is how they look when the exposures are combined. Rubin's wide field and frequent imaging make it uniquely capable of detecting and tracking asteroids, comets, and distant trans-Neptunian objects – building a detailed inventory of our Solar System and helping protect Earth by alerting scientists to potentially hazardous objects.

This image also offers a starting point for watching the ever-changing sky. Rubin will return to this same region many times over the coming decade, catching brief but important events like supernova explosions and the flares from stars as they are consumed by hungry black holes. Rubin's software will automatically compare new images to templates built from previous images, identifying up to 10 million changes each night and providing insight into short-lived cosmic phenomena and objects in motion.

On the largest scales, scientists will use Rubin's observations of galaxies like those seen here to investigate two of the Universe's biggest mysteries: dark matter and dark energy. By mapping the shapes and distributions of galaxies over time, scientists can infer the underlying structure of dark matter and observe how the expansion of the Universe is being influenced by dark energy.

The image was captured by Rubin Observatory using the 3200-megapixel LSST Camera – the largest digital camera in the world. Rubin Observatory will scan the sky every night for 10 years, creating an ultra-wide, ultra-high-definition, time-lapse record of our Universe.

Image Credit: NSF–DOE Vera C. Rubin Observatory/NOIRLab/SLAC/AURA

Image enhancement: Jean-Baptiste Faure

Open Cluster M21 as seen by Rubin

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Messier 21 or M21, also designated NGC 6531 or Webb's Cross, is an open cluster of stars located to the north-east of Sagittarius in the night sky, close to the Messier objects M20 to M25 (except M24). Here, it is imaged by NSF–DOE Vera C. Rubin Observatory. It was discovered and catalogued by Charles Messier on June 5, 1764. This cluster is relatively young and tightly packed. A few blue giant stars have been identified in the cluster, but Messier 21 is composed mainly of small dim stars. With a magnitude of 6.5, M21 is not visible to the naked eye; however, with the smallest binoculars it can be easily spotted on a dark night. The cluster is positioned near the Trifid Nebula (NGC 6514), but is not associated with that nebulosity. It forms part of the Sagittarius OB1 association.

This cluster is located 1,205 pc away from Earth with an extinction of 0.87. Messier 21 is around 6.6 million years old with a mass of 783.4 M☉. It has a tidal radius of 11.7 pc, with a nucleus radius of 1.6±0.1 pc and a coronal radius of 3.6±0.2 pc. There are at least 105±11 members within the coronal radius down to visual magnitude 15.5, including many early B-type stars. An estimated 40–60 of the observed low-mass members are expected to be pre-main-sequence stars,[8] with 26 candidates identified based upon hydrogen alpha emission and the presence of lithium in the spectrum. The stars in the cluster do not show a significant spread in ages, suggesting that the star formation was triggered all at once.

Image Credit: RubinObs/NOIRLab/SLAC/NSF/DOE/AURA

Image enhancement: Jean-Baptiste Faure

Lenticular Galaxy NGC 7722

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For this picture from the Hubble Space Telescope, we have a sight of an uncommon galaxy with a striking appearance. This is NGC 7722, a lenticular galaxy located about 187 million light-years away in the constellation Pegasus.

A "lenticular", meaning "lens-shaped", galaxy is a type that sits in between the more familiar spiral galaxies and elliptical galaxies. It is also less common than these – partly because when a galaxy has an ambiguous appearance, it can be hard to determine if it is actually a spiral, actually an elliptical galaxy, or something in between. Many of the known lenticular galaxies sport features of both spiral and elliptical galaxies. In this case, NGC 7722 lacks the defined arms of a spiral galaxy, while it has an extended, glowing halo and a bright bulge in the center similar to an elliptical galaxy. Unlike elliptical galaxies, it has a visible disc – concentric rings swirl around its bright nucleus. Its most prominent feature, however, is undoubtedly the long lanes of dark red dust coiling around the outer disc and halo.

This new Hubble image, the sharpest yet taken of NGC 7722, brings the impressive dust lanes into sharp focus. Bands of dust like this are not uncommon in lenticular galaxies, and they stand out against the broad, smooth halo of light that typically surrounds lenticular galaxies. The distinctive dust lanes of NGC 7722 are thought to result from a merger with another galaxy in the past, similar to other lenticular galaxies. It is not yet fully understood how lenticular galaxies form, but mergers and other gravitational interactions are thought to play an important part, reshaping galaxies and exhausting their supplies of gas while bringing new dust.

While it doesn't host as many new, young stars as a spiral galaxy, there's still activity in NGC 7722: in 2020 it was host to the explosion of a star that could be detected from Earth. SN 2020SSF was a Type Ia supernova, an event which occurs when a white dwarf star in a binary system siphons enough mass away from its companion star that it grows unstable and explodes. These explosions output a remarkably consistent level of light: by measuring how bright they appear from Earth and comparing against how bright they really are, it's possible to tell how far away they must be. Type Ia supernovae are one of the best ways to measure distances to galaxies, so understanding exactly how they work is of great importance to astronomers.

Taken with Hubble's Wide Field Camera 3, this Hubble image was obtained as part of an observing programme (#16691, PI: R. J. Foley) that followed up on recent supernovae. SN 2020SSF is not visible in this image, as it was actually taken two years later, when the supernova had long faded. This was on purpose: the aim of the observations was to witness the aftereffects of the supernova and examine its surroundings, which can only be done once the intense light of the explosion is gone. With Hubble's clear vision, astronomers can search for radioactive material created by the supernova, catalogue its neighbours to see how old the star likely was, and look for the companion star it left behind – all from almost 200 million light-years away.

Image Credit: ESA/Hubble and NASA, R. J. Foley (UC Santa Cruz), Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA

Acknowledgement: Mehmet Yüksek

Image enhancement: Jean-Baptiste Faure

Planetary Nebula PMR 1 as seen by Webb

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Two heads are better than one in the latest images from NASA's James Webb Space Telescope, which reveal new detail in a mysterious, little-studied nebula surrounding a dying star.

Nebula PMR 1 is a cloud of gas and dust that bears an uncanny resemblance to a brain in a transparent skull, inspiring its nickname, the "Exposed Cranium" nebula. Webb captured its unusual features in both near- and mid-infrared light. The nebula was first revealed in infrared light by a predecessor to Webb, NASA's now-retired Spitzer Space Telescope, more than a decade ago. Webb's advanced instruments show detail that enhances the nebula's brain-like appearance.

The nebula appears to have distinct regions that capture different phases of its evolution – an outer shell of gas that was blown off first and consists mostly of hydrogen, and an inner cloud with more structure that contains a mix of different gases. Both Webb's NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) show a distinctive dark lane running vertically through the middle of the nebula that defines its brain-like look of left and right hemispheres. Webb's resolution shows that this lane could be related to an outburst or outflow from the central star, which typically occurs as twin jets burst out in opposite directions. Evidence for this is particularly notable at the top of the nebula in Webb’s MIRI image, where it looks like the inner gas is being ejected outward.

While there is still much to be understood about this nebula, it's clear that it is being created by a star near the end of its fuel-burning "life". In their end stages, stars expel their outer layers. It's a dynamic and fairly fast process, in cosmic terms. Webb has captured a moment in this star's decline. What ultimately happens will depend on the mass of the star, which is yet to be determined. If it's massive enough, it will explode in a supernova. A less massive Sun-like star will continue to shed layers until only its core remains as a dense white dwarf, which will cool off over eons.

Image Credit: NASA, ESA, CSA, STScI, Image Processing: Joseph DePasquale (STScI)

Image enhancement: Jean-Baptiste Faure