Starship Asterisk*

Stars and galaxies, mostly reddish in colour, are scattered across a dark background. In the foreground upper-right corner, a large elliptical galaxy is surrounded by many smaller similar galaxies in a cluster. These galaxies have bright centres and a diffuse white glow around them. The large galaxy has distorted images and arcs around it.

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Image Credit: ESA/Webb, NASA & CSA, P. Kelly

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This observation from the NASA/ESA/CSA James Webb Space Telescope features the massive galaxy cluster RX J2129. Due to Gravitational lensing, this observation contains three different images of the same supernova-hosting galaxy, which you can see in closer detail here. Gravitational lensing occurs when a massive celestial body causes a sufficient curvature of spacetime to bend the path of light travelling past or through it, almost like a vast lens. In this case, the lens is the galaxy cluster RX J2129, located around 3.2 billion light-years from Earth in the constellation Aquarius. Gravitational lensing can cause background objects to appear strangely distorted, as can be seen by the concentric arcs of light in the upper right of this image.

Astronomers discovered the supernova in the triply-lensed background galaxy using observations from the NASA/ESA Hubble Space Telescope, and they suspected that they had found a very distant Type Ia supernova. These supernovae always produce a fairly consistent luminosity — at the same distance, one looks as bright as any other — which makes them particularly helpful to astronomers. As their distance from Earth is proportional to how dim they appear in the night sky, objects with known brightness can be used as 'standard candles' to measure astronomical distances.

The almost uniform luminosity of a Type Ia supernova could also allow astronomers to understand how strongly the galaxy cluster RX J2129 is magnifying background objects, and therefore how massive the galaxy cluster is. As well as distorting the images of background objects, gravitational lenses can cause distant objects to appear much brighter than they would otherwise. If the gravitational lens magnifies something with a known brightness, such as a Type Ia supernova, then astronomers can use this to measure the ‘prescription’ of the gravitational lens.

A spiral galaxy lies just off-centre. It has large, faint, reddish spiral arms and a bright, reddish core. These lie over two brighter blue spiral arms. These are patchy, with blotches of star formation. Long trails of these bright blotches trail down from the lower spiral arm, resembling tendrils. The background is black, lightly scattered with small galaxies and stars, and a larger elliptical galaxy in one corner.

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Image Credit: ESA/Hubble & NASA, M. Gullieuszik

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A jellyfish galaxy with trailing tentacles of stars hangs in inky blackness in this image from the NASA/ESA Hubble Space Telescope. As Jellyfish galaxies move through intergalactic space they are slowly stripped of gas, which trails behind the galaxy in tendrils illuminated by clumps of star formation. These blue tendrils are visible drifting below the core of this galaxy, and give it its jellyfish-like appearance. This particular jellyfish galaxy — known as JO201 (aka Ka 364) — lies in the constellation Cetus, which is named after a sea monster from ancient Greek mythology. This sea-monster-themed constellation adds to the nautical theme of this image.

The tendrils of jellyfish galaxies extend beyond the bright disc of the galaxy core. This particular observation comes from an investigation into the sizes, masses and ages of the clumps of star formation in the tendrils of jellyfish galaxies. Astronomers hope that this will provide a breakthrough in understanding the connection between ram-pressure stripping — the process that creates the tendrils of jellyfish galaxies — and star formation.

This galactic seascape was captured by Wide Field Camera 3 (WFC3), a versatile instrument that captures images at ultraviolet and visible wavelengths. WFC3 is the source of some of Hubble’s most spectacular images, from a view of Jupiter and Europa to a revisit to the Pillars of Creation.

• arXiv > astro-ph > arXiv:2301.08279 > 19 Jan 2023

• arXiv > astro-ph > arXiv:2302.10615 > 21 Feb 2023

Click to view full size image 1 or image 2

Image Credit: Zdeněk Bardon (bardon.cz)/ESO

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In this Picture of the Week, Venus is shining brightly over ESO’s La Silla Observatory in Chile. The picture was taken just before dawn, towards the East, and also features the diffuse zodiacal light –– sunlight scattered by dust particles in the Solar System.

The three domes to the left of the road are the BlackGEM telescopes, built by Radboud University, the Netherlands Research School for Astronomy (NOVA), and KU Leuven. BlackGEM will search for the afterglow of some of the most dramatic events in the Universe, such as the collision of black holes and neutron stars. The ripples in space and time generated by these violent events can be detected by the LIGO and Virgo observatories. Thanks to their large field of view, the BlackGEM telescopes can locate the source of visible light from the afterglow of these events, and thereby pinpoint where the collision took place. This allows astronomers to study in greater detail what happens when black holes and neutron stars merge.

A cluster of large galaxies, surrounded by various stars and smaller galaxies on a dark background. The central cluster is mostly made of bright elliptical galaxies that are surrounded by a warm glow. Nearby the cluster is the stretched, distorted arc of a galaxy, gravitationally lensed by the cluster.

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Image Credit: ESA/Hubble & NASA, H. Ebeling

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A massive galaxy cluster in the constellation Cetus dominates the centre of this image from the NASA/ESA Hubble Space Telescope. This image is populated with a serene collection of elliptical and spiral galaxies, but galaxies surrounding the central cluster — which is named SPT-CL J0019-2026 — appear stretched into bright arcs, as if distorted by a gargantuan magnifying glass. This cosmic contortion is called gravitational lensing, and it occurs when a massive object like a galaxy cluster has a sufficiently powerful gravitational field to distort and magnify the light from background objects. Gravitational lenses magnify light from objects that would usually be too distant and faint to observe, and so these lenses can extend Hubble’s view even deeper into the Universe.

This observation is part of an ongoing project to fill short gaps in Hubble’s observing schedule by systematically exploring the most massive galaxy clusters in the distant Universe, in the hopes of identifying promising targets for further study with both Hubble and the NASA/ESA/CSA James Webb Space Telescope. This particular galaxy cluster lies at a vast distance of 4.6 billion light years from Earth.

Each year, the Space Telescope Science Institute is inundated with observing proposals for Hubble, in which astronomers suggest targets for observation. Even after selecting only the very best proposals, scheduling observations of all of Hubble’s targets for a year is a formidable task. There is sometimes a small fraction of observing time left unused in Hubble’s schedule, so in its ‘spare time’ the telescope has a collection of objects to explore — including the lensing galaxy cluster shown in this image.

Image Credit: ESO/Mesa, De Rosa et al

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No, you’re not seeing double: this Picture of the Week shows two images of a Jupiter-like planet that orbits the star AF Leporis. The planet has been imaged by two independent groups of astronomers using the SPHERE instrument on ESO’s Very Large Telescope (VLT) in Chile. But why did they target this particular star?

The two groups, led by Dino Mesa (INAF, Italy) and Robert De Rosa (ESO, Chile), studied star catalogues from the European Space Agency’s Hipparcos and Gaia satellites. Over the years, these two space missions have accurately pinpointed the position and motion of stars in our galaxy using astrometry. Planets exert a gravitational tug on their host stars, perturbing their trajectory on the sky. The two teams found that the star AF Leporis exhibited such a disturbed trajectory, a telltale sign that a planet could be hiding there.

As the two groups took a closer look at this system with the VLT, they managed to directly image the planet that orbits AF Leporis. They both used the SPHERE instrument, which corrects the blurring caused by atmospheric turbulence using adaptive optics, and also blocks the light from the star with a special mask, revealing the planet next to it. They found that the planet is just a few times more massive than Jupiter, making it the lightest exoplanet detected with the combined use of astrometric measurements and direct imaging.

The AF Leporis system shares similar features to our Solar System. The star has roughly the same mass, size and temperature as the Sun, and the planet orbits it at a distance similar to that between Saturn and the Sun. The system also has a debris belt with similar characteristics as the Kuiper belt. Since the AF Leporis system is only 24 million years old ––about 200 times younger than the Sun–– further studies of this system can shed light on how our own Solar System was formed.

• arXiv > astro-ph > arXiv:2302.06213 > 13 Feb 2023

• arXiv > astro-ph > arXiv:2302.06332 > 13 Feb 2023

• arXiv > astro-ph > arXiv:2302.05420 > 10 Feb 2023

Image Credit: Gemini Observatory/NOIRLab/NSF/AURA/P. Michaud

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Gemini North, one half of the International Gemini Observatory, operated by NSF’s NOIRLab, looks distinctly peculiar in this week’s Image of the Week. Photographs of the telescopes are often taken during the day, and so the telescope domes are closed in a lot of images. Even when the dome is open, only part of the dome is ajar. However, in this image, we see the entire top of the telescope directed at an object in the night sky! The photographer created this curious image by capturing a dozen images of the observatory as the dome turned a full 180 degrees and then stacking the images together. With this photographic trick, it appears the dome has become mysteriously transparent. The odd, brightly lit appearance of Gemini North is juxtaposed with the sprawling brilliance of the Milky Way overhead.

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This colliding trio — known to astronomers as SDSSCGB 10189 — is a relatively rare combination of three large star-forming galaxies lying within only 50 000 light-years of one another.

Three galaxies stand together just right of centre. They are close enough that they appear to be merging into one. Their shapes are distorted, with strands of gas and dust running between them. Each is emitting a lot of light. Further to the left is an unconnected, dimmer spiral galaxy. The background is dark, with a few smaller, dim and faint galaxies and a couple of stars.

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Image Credit: ESA/Hubble & NASA, M. Sun

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A spectacular trio of merging galaxies in the constellation Boötes takes centre stage in this image from the NASA/ESA Hubble Space Telescope. These three galaxies are set on a collision course and will eventually merge into a single larger galaxy, distorting one another’s spiral structure through mutual gravitational interaction in the process. An unrelated foreground galaxy appears to float serenely alongside the collision, and the smudged shapes of much more distant galaxies are visible in the background.

This colliding trio — known to astronomers as SDSSCGB 10189 — is a relatively rare combination of three large star-forming galaxies lying within only 50 000 light-years of one another. While that might sound like a safe distance, for galaxies this makes them extremely close neighbours! Our own galactic neighbours are much further away; Andromeda, the nearest large galaxy to the Milky Way, is more than 2.5 million light-years away from Earth.

This observation was designed to help astronomers understand the origin of the largest, most massive galaxies in the universe. These galactic behemoths are called Brightest Cluster Galaxies (BCGs) and — as the name suggests — are defined as the brightest galaxies in any given galaxy cluster. Astronomers suspect that BCGs form through the merger of large, gas-rich galaxies like the ones in this image. They turned to Hubble’s Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) to investigate this galactic trio in painstaking detail, hoping to shed light on the formation of the Universe’s most massive galaxies.

Image Credit: Zdeněk Bardon/ESO

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The Atacama Desert of Chile is one of the driest places on Earth, with extremely reliable weather, making it an excellent site to explore the Universe. So it’s not strange that this is the place ESO has chosen to place the flagship facilities for European ground-based astronomy.

At 2635 meters above sea level in the Atacama Desert, we find ESO’s Paranal Observatory, seen on the far mountain top in this image. It hosts several world-class telescopes like the Very Large Telescope (VLT), and the Visible and Infrared Survey Telescope for Astronomy (VISTA), the latter located on its own peak, seen here to the right of the main one.

But the desert is good for other astronomy related sciences as well: Mars explorations! The red and rocky environment around Paranal has a strong resemblance to Mars, making it a perfect site for the European Space Agency (ESA) to test their Mars rovers.

Credit: Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA/G. Donatiello Image processing: D. de Martin (NSF’s NOIRLab) & M. Zamani (NSF’s NOIRLab)

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The smudge in the center of this image from the Dark Energy Camera (DECam), built by the US Department of Energy, is the elusive dwarf galaxy Donatiello II. It is one of six dwarf galaxies discovered by Italian amateur astronomer Giuseppe Donatiello. Three of them — Donatiello II, III and IV — were tucked away in the DECam images, and are now known to be satellites of the Sculptor Galaxy (NGC 253) (outside the field, to the far right).

DECam is an instrument on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), a Program of NSF’s NOIRLab. It combines a wide field of view with high sensitivity, meaning that it can scan large swathes of the night sky and also pick out the faint stars making up neighboring dwarf galaxies such as this one.

The Milky Way shares its patch of the Universe with a whole host of small galaxies and star clusters, which help astronomers shed light on the yet-to-be-understood physics of dark matter.