Starship Asterisk*

A spiral galaxy. It is tilted diagonally, and slightly towards the viewer, making its core and disc separately visible. Its disc is speckled by small stars, has threads of dark reddish dust and bubbles of bright, glowing gas. The core shines brightly in a warmer colour. Several tiny stars and small galaxies are included in the black background. Credit: ESA/Hubble & NASA, C. Kilpatrick

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The spiral galaxy NGC 298 basks in this image from the NASA/ESA Hubble Space Telescope. NGC 298 lies around 89 million light-years away in the constellation Cetus, and appears isolated in this image — only a handful of distant galaxies and foreground stars accompany the lonely galaxy. While NGC 298 seems peaceful, in 1986 it was host to one of astronomy's most extreme events: a catastrophic stellar explosion known as a Type II supernova.

Hubble’s Advanced Camera for Surveys captured NGC 298 as part of an investigation into the origins of Type II supernovae. All Type II supernovae are produced by the collapse and subsequent explosion of young, massive stars, but they can produce a spectacular diversity of brightnesses and spectral features.

Astronomers suspect that the diversity of this cosmic firework show might be due to gas and dust being stripped from the stars that will eventually produce Type II supernovae. Observing the region surrounding supernova explosions can reveal traces of the progenitor star’s history preserved in this lost mass, as well as revealing any companion stars that survived the supernova. Hubble used the brief periods between scheduled observations to explore the aftermath of a number of Type II supernovae, hoping to piece together the relationship between Type II supernovae and the stellar systems which give rise to them.

Credit: ESO/VPHAS+ team. Acknowledgement: Cambridge Astronomical Survey Unit

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Sometimes dramatic events are needed to create something stunning. This beautiful structure of filaments and clouds in the southern constellation of Vela are all that remains of a massive star that died in a powerful explosion known as supernova. This is a small section of a larger image taken using the wide-field camera OmegaCAM at the VLT Survey Telescope (VST). Hosted at ESO’s Paranal Observatory in the Chilean desert, the VST is one of the best telescopes in the world to take large images of the sky in visible light.

Even though bright stars populate this image, it's hard to not be captivated by the pink gaseous clouds filling up the frame. Some tiny, others thicker, the filaments stretch outwards like tentacles. As they intertwine and cling together, an intricate network is formed which mixes with blurred clouds. But how did they come to be like this?

Around 11 000 years ago, a massive star exploded as a supernova, ejecting its outer layers. The explosion also generated shock waves which traveled outwards, compressing the gas around the star and creating the intricate network visible in the image. The result of such explosions are called supernova remnants. At 800 light years away from Earth, the Vela supernova remnant is one of the closest known to us.

Image Credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. Chu

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Star trails blur and lasers streak across the sky in this long-exposure view from Pu‘u Poli‘ahu, the mountain peak adjacent to the Gemini North telescope of the International Gemini Observatory, operated by NSF’s NOIRLab. Gemini North can be seen slightly to the right of the center of this image, shooting its laser into the sky. A handful of other telescopes that are part of the Maunakea Observatories in Hawai‘i surround Gemini North.

Despite resembling searchlights or a battle from a sci-fi film, the lasers in this image play a vital role in correcting the vision of Gemini and the other cutting-edge telescopes. They are part of these telescopes’ adaptive optics systems, and help astronomers measure the distortions in their data caused by atmospheric turbulence. By continuously feeding these measurements into computer-controlled deformable mirrors, astronomers can compensate for almost all of the blurring caused by Earth’s atmosphere. This provides Gemini North with a crystal-clear view of the night sky, rivaling that of a space telescope above the tumultuous atmosphere.

A spiral galaxy. It is large in the centre with a lot of detail visible. The core glows brightly and is surrounded by concentric rings of dark and light dust. The spiral arms are thick and puffy with grey dust and glowing blue areas of star formation. They wrap around the galaxy to form a ring. Part of the arm is drawn out into a dark thread above the galaxy, and dust from the arm trails off to the right.

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Image Credit: ESA/Hubble & NASA, M. Gullieuszik and the GASP team

The jellyfish galaxy JW39 hangs serenely in this image from the NASA/ESA Hubble Space Telescope. This galaxy lies over 900 million light-years away in the constellation Coma Berenices, and is one of several jellyfish galaxies that Hubble has been studying over the past two years.

Despite this jellyfish galaxy’s serene appearance, it is adrift in a ferociously hostile environment; a galaxy cluster. Compared to their more isolated counterparts, the galaxies in galaxy clusters are often distorted by the gravitational pull of larger neighbours, which can twist galaxies into a variety of weird and wonderful shapes. If that was not enough, the space between galaxies in a cluster is also pervaded with a searingly hot plasma known as the intracluster medium. While this plasma is extremely tenuous, galaxies moving through it experience it almost like swimmers fighting against a current, and this interaction can strip galaxies of their star-forming gas.

This interaction between the intracluster medium and the galaxies is called ram-pressure stripping, and is the process responsible for the trailing tendrils of this jellyfish galaxy. As JW39 has moved through the cluster the pressure of the intracluster medium has stripped away gas and dust into long trailing ribbons of star formation that now stretch away from the disc of the galaxy.

Astronomers using Hubble’s Wide Field Camera 3 studied these trailing tendrils in detail, as they are a particularly extreme environment for star formation. Surprisingly, they found that star formation in the ‘tentacles’ of jellyfish galaxies was not noticeably different from star formation in the galaxy disc.

• Astrophysical Journal 945(1):54 (2023 Mar 01) DOI: 10.3847/1538-4357/acb59b
• arXiv > astro-ph > arXiv:2301.08279 > 19 Jan 2023

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

Credit: ESO

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A lot can change in more than two decades — just take a look at these pictures of ESO’s Very Large Telescope (VLT)! On the left we see the VLT when it was still under construction atop Cerro Paranal in Chile, while on the right we see it in all its glory as it stands today.

Before building the telescopes themselves the mountain had to be lowered by 28 metres to create the telescope platform, which meant removing some 350 000 cubic metres of rock. Then in 1998 the Unit Telescope UT1 (Antu), the leftmost telescope and the furthest along in its construction in the “then” picture, captured its first image of the cosmos — 25 years ago this week. Today, the VLT consists of four Unit Telescopes with main mirrors of 8.2 metres diameter and four movable 1.8-metre diameter Auxiliary Telescopes.

After a quarter of a century of observations, the VLT remains one of the world’s most advanced optical/infrared telescopes and is continuing to make key discoveries, and it’s being upgraded to help it pursue its mission to uncover the secrets of the Universe. These upgrades will ensure the VLT maintains its position at the forefront of science and engineering for years to come.

Happy Birthday VLT!

Image Credit: Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA Processing: R. Colombari and M. Zamani (NOIRLab)

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NGC 1808 is a barred spiral galaxy located in the southern constellation Columba (the dove). This image was captured using the Dark Energy Camera (DECam), which is mounted on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO), a Program of NSF’s NOIRLab, in Chile.

The core of NGC 1808 is thought to house a supermassive black hole, characterized by its accretion of material and higher-than-normal brightness. The smoldering center is closely surrounded by a faint blue ring populated with star clusters and supernova remnants. This region is defined by its starburst activity, producing an exceptional number of hot, bright, young stars. The abundance of rapid star formation is thought to be the result of past tidal interactions with the nearby galaxy NGC 1792. Laced throughout this middle region of NGC 1808 are dark dust lanes resulting from large outflows of hydrogen gas from the galactic nucleus. The softly glowing outer arms surrounding the galaxy are slightly warped, again pointing to tidal interactions with NGC 1792. Such an interaction could have created the asymmetrical shape of NGC 1808 and hurled gas towards the nucleus, igniting the rapid star formation in its surrounding ring.

A dense cluster of bright stars. The core of the cluster is to the left and has a distinct
group of blue stars. Surrounding the core are a multitude of stars in warmer colours.
These stars are very numerous near the core and become more and more sparse, and
more small and distant, out to the sides of the image. A few larger stars also stand in the
foreground near the edges of the image. Credit: ESA/Hubble & NASA, E. Noyola, R. Cohen

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The densely packed globular cluster NGC 6325 glistens in this image from the NASA/ESA Hubble Space Telescope. This concentrated group of stars lies around 26 000 light years from Earth in the constellation Ophiuchus.

Globular clusters like NGC 6325 are tightly bound collections of stars with anywhere from tens of thousands to millions of members. They can be found in all types of galaxies, and act as natural laboratories for astronomers studying star formation. This is because the constituent stars of globular clusters tend to form at roughly the same time and with similar initial composition, meaning that astronomers can use them to fine-tune their theories of how stars evolve.

Astronomers inspected this particular cluster not to understand star formation, but to search for a hidden monster. Though it might look peaceful, astronomers suspect this cluster could contain an intermediate-mass black hole that is subtly affecting the motion of surrounding stars. Previous research found that the distribution of stars in some highly concentrated globular clusters — those with stars packed relatively tightly together — was slightly different from what astronomers expected.

This discrepancy suggested that at least some of these densely packed globular clusters — including perhaps NGC 6325 — could have a black hole lurking at the centre. To explore this hypothesis further, astronomers turned to Hubble’s Wide Field Camera 3 to observe a larger sample of densely populated globular clusters, which included this star-studded image of NGC 6325. Additional data from Hubble’s Advanced Camera for Surveys were also incorporated into this image.

Image Credit: ESO/F. Selman

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Have you ever seen a sunset so red? Probably not, since the cause of this reddened twilight sky is something quite dramatic: a volcanic eruption. This Picture of the Week was captured at ESO’s Paranal Observatory in Chile; under the Milky Way, on the top of the dark silhouette of Cerro Paranal, ESO’s Very Large Telescope looks upwards to the sky.

On 15 January 2022, the submarine volcano Hunga Tonga–Hunga Ha‘apai erupted in the southern Pacific Ocean. This eruption created shock waves that rippled through the atmosphere, reaching places far from the volcano itself. At ESO’s Paranal and La Silla observatories in Chile, more than 10 000 kilometres away, weather stations detected these atmospheric disturbances.

The eruption also launched an ash plume 57 kilometres tall, releasing massive quantities of particles into the atmosphere, including water vapour and dust. Sunlight is scattered and reddened by these tiny dust particles, and this effect was detected in calibration images taken during twilight by several ESO telescopes. This Picture of the Week, taken 6 months after the eruption, shows that the effects of these particles were not transitory. At the time of writing, one year later, the sky has still not returned to its pre-eruption state.

Image Credit: KPNO/NOIRLab/NSF/AURA/T. Slovinský

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The dynamic coloring of the night sky at Kitt Peak National Observatory (KPNO), a Program of NSF’s NOIRLab, makes for a beautiful backdrop behind the UArizona Bok 2.3-meter Telescope. Distant city lights, cars, airglow, and the arc of the Milky Way all add to the variety of colors. Zodiacal light emanating from the horizon intersects with the Milky Way on the right hand side of the image.

One orange star at the center of this image stands out amongst the rest. This is the red supergiant Betelgeuse, a star that marks a ‘shoulder’ of the hunter constellation, Orion. Being a relatively old star, Betelgeuse glows a cool red compared to its hot, bright blue neighbors. Despite this, it is usually the 10th brightest star in the night sky. More compellingly, Betelgeuse is massive — so massive that its diameter is more than 750 times that as the Sun. This makes it the largest star visible to the naked eye. Betelgeuse received some press in 2019 when a small explosion on its surface was observed, leading to speculation that a supernova was imminent. However, in 2021 scientists determined that the dying star won’t be exploding for at least another 100,000 years.

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. Close to the cluster core is the stretched, distorted arc of a galaxy, gravitationally lensed by the cluster. Credit: ESA/Hubble & NASA, H. Ebeling

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A vast galaxy cluster lurks in the centre of this image from the NASA/ESA Hubble Space Telescope. Like a submerged sea monster causing waves on the surface, this cosmic leviathan can be identified by the distortions in spacetime around it. The mass of the cluster has caused the images of background galaxies to be gravitationally lensed; the galaxy cluster has caused a sufficient curvature of spacetime to bend the path of light and cause background galaxies to appear distorted into streaks and arcs of light. A host of other galaxies can be seen surrounding the cluster, and a handful of foreground stars with tell-tale diffraction spikes are scattered throughout the image.

This particular galaxy cluster is called eMACS J1823.1+7822, and lies almost nine billion light-years away in the constellation Draco. It is one of five exceptionally massive galaxy clusters explored by Hubble in the hopes of measuring the strengths of these gravitational lenses and providing insights into the distribution of dark matter in galaxy clusters. Strong gravitational lenses like eMACS J1823.1+7822 can help astronomers study distant galaxies by acting as vast natural telescopes which magnify objects that would otherwise be too faint or distant to resolve.

This multiwavelength image layers data from eight different filters and two different instruments: Hubble’s Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3). Both instruments have the ability to view astronomical objects in just a small slice of the electromagnetic spectrum using filters, which allow astronomers to image objects at precisely selected wavelengths. The combination of observations at different wavelengths lets astronomers develop a more complete picture of the structure, composition and behaviour of an object than visible light alone would reveal.

Image Credit: Zdeněk Bardon/ESO

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The telescope peeking out from its dome is the 1.52-metre telescope at La Silla Observatory. Being over 55 years old, the 1.52-metre is one of the oldest telescopes at ESO and it has participated in laying the foundation for many areas of astronomical research.

Being a special telescope in many ways, it also has a twin, the 1.52-metre telescope at the Observatoire de Haute Provence in France. Both telescopes were specifically designed to do stellar spectroscopy and astrophotography, and the 1.52-m in La Silla involved no less than five instruments, including the B&C spectrograph. This instrument captured the spectrum of the Hale-Bopp comet as it passed by in 1995, one of the first recorded spectrums of a comet.

After over 30 years of service, the 1.52-m at La Silla was decommissioned in 2002. Still sitting in its dome, it peers out over the vast Atacama Desert, and we get to marvel about all the things it has seen in the night sky.