Starship Asterisk*

Image Credit: ESO/PHANGS

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This week, we feature an image of the spiral galaxy NGC 4303, also known as Messier 61, which is one of the largest galactic members of the Virgo Cluster. Being a so-called starburst galaxy, it has an unusually high amount of stars being born, and has been used by astronomers as a laboratory to better understand the fascinating phenomena of star formation.

Stars form when clouds of cold gas collapse. The energetic radiation from newly born stars will heat and ionise the surrounding remaining gas. The ionised gas will shine, acting as a beacon of ongoing star formation. In this stunning and jewel-like image, this glowing gas can be seen as the whirlpool of gold: the direct traces of stars being born.

The golden glow is a result of combining observations taken at different wavelengths of light with the Multi-Unit Spectroscopic Explorer (MUSE) instrument on ESO’s Very Large Telescope (VLT) in Chile. Here gas clouds of ionised oxygen, hydrogen and sulphur are shown in blue, green and red, respectively. The observations are done as part of the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) project, aiming to reveal nearby galaxies across all wavelengths of the electromagnetic spectrum. ...

Image Credit: ESA/Hubble & NASA, R. Cohen

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This star-studded image from the NASA/ESA Hubble Space Telescope shows the heart of the globular cluster NGC 6638 in the constellation Sagittarius. The star-strewn observation highlights the density of stars at the heart of globular clusters, which are stable, tightly bound clusters of tens of thousands to millions of stars. To capture the data in this image, Hubble used two of its cutting-edge astronomical instruments: Wide Field Camera 3 (WFC3) and the Advanced Camera for Surveys (ACS).

Hubble revolutionised the study of globular clusters, as it is almost impossible to clearly distinguish the stars in globular clusters with ground-based telescopes. The blurring caused by Earth’s atmosphere makes it impossible to tell one star from another, but from Hubble’s location in low Earth orbit the atmosphere no longer poses a problem. As a result, Hubble has been used to study what kind of stars globular clusters are made up of, how they evolve, and the role of gravity in these dense systems.

The NASA/ESA/CSA James Webb Space Telescope will further our understanding of globular clusters by peering into those globular clusters that are currently obscured by dust. Webb will predominantly observe at infrared wavelengths, which are less affected by the gas and dust surrounding newborn stars. This will allow astronomers to inspect star clusters that are freshly formed, providing insights into stellar populations before they have a chance to evolve.

Image Credit: ESO/Mahdi Zamani

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This Picture of the Week shows a stunning view of the Milky Way as it stretches over the Atacama Desert, home to ESO’s Paranal Observatory. In the foreground, we also get a glimpse of the planet hunter NGTS, the Next Generation Transit Survey.

NGTS, built by a collaboration of UK, Swiss and German institutions, consists of 12 telescopes that continuously monitor the sky, looking for dips in the brightness of hundreds of thousands of stars. As an exoplanet transits between its host star and us, it dims the light reaching us, which can be picked up by NGTS. The survey specialises in looking for super-Earths, exoplanets more massive than our home planet but lighter than an ice giant like Neptune. NGTS also works in tandem with ESO telescopes, like the ones visible in the background: the Very Large Telescope (VLT, with its adaptive optics lasers) and the Visible and Infrared Survey Telescope for Astronomy (VISTA) to the right.

When NGTS detects new planet candidates, ESO instruments, such as the exoplanet specialists HARPS at ESO’s La Silla Observatory or ESPRESSO at the VLT, can do follow-up observations. From these observations we can learn about the masses of these exoplanets and compositions of their atmospheres. With the combined power of these facilities, the exoplanets of the Milky Way are being studied with the highest possible precision and detail there is.

Image Credit: ESA/Hubble & NASA, J. Bally; Acknowledgement: M. H. Özsaraç

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This celestial cloudscape from the NASA/ESA Hubble Space Telescope captures the colourful region surrounding the Herbig-Haro object HH 505. Herbig-Haro objects are luminous regions surrounding newborn stars, and are formed when stellar winds or jets of gas spewing from these newborn stars form shockwaves colliding with nearby gas and dust at high speeds. In the case of HH 505, these outflows originate from the star IX Ori, which lies on the outskirts of the Orion Nebula around 1000 light-years from Earth. The outflows themselves are visible as gracefully curving structures at the top and bottom of this image, and are distorted into sinuous curves by their interaction with the large-scale flow of gas and dust from the core of the Orion Nebula.

This observation was captured with Hubble’s Advanced Camera for Surveys (ACS) by astronomers studying the properties of outflows and protoplanetary discs. The Orion Nebula is awash in intense ultraviolet radiation from bright young stars. The shockwaves formed by the outflows are brightly visible to Hubble, but the slower-moving currents of stellar material are also highlighted by this radiation. That allows astronomers to directly observe jets and outflows and learn more about their structures.

The Orion Nebula is a dynamic region of dust and gas where thousands of stars are forming, and is the closest region of massive star formation to Earth. As a result, it is one of the most scrutinised areas of the night sky and has often been a target for Hubble. This observation was also part of a spellbinding Hubble mosaic of the Orion Nebula, which combined 520 ACS images in five different colours to create the sharpest view ever taken of the region.

Image Credit: Gemini Observatory/NOIRLab/NSF/AURA Processing: T.A. Rector (Univ of Alaska Anchorage/NOIRLab), J. Miller (Gemini Observatory/NOIRLab), M. Zamani & D. de Martin (NOIRLab)

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An evocative new image captured by the Gemini North telescope in Hawai‘i reveals a pair of interacting spiral galaxies — NGC 4568 and NGC 4567 — as they begin to clash and merge. These galaxies are entangled by their mutual gravitational field and will eventually combine to form a single elliptical galaxy in around 500 million years. Also visible in the image is the glowing remains of a supernova that was detected in 2020.

Gemini North, one of the twin telescopes of the International Gemini Observatory, operated by NSF’s NOIRLab, has observed the initial stages of a cosmic collision approximately 60 million light-years away in the direction of the constellation Virgo. The two stately spiral galaxies, NGC 4568 (bottom) and NGC 4567 (top), are poised to undergo one of the most spectacular events in the Universe, a galactic merger. At present, the centers of these galaxies are still 20,000 light-years apart (about the distance from Earth to the center of the Milky Way) and each galaxy still retains its original, pinwheel shape. Those placid conditions, however, will change.

As NGC 4568 and NGC 4567 draw together and coalesce, their dueling gravitational forces will trigger bursts of intense stellar formation and wildly distort their once-majestic structures. Over millions of years, the galaxies will repeatedly swing past each other in ever-tightening loops, drawing out long streamers of stars and gas until their individual structures are so thoroughly mixed that a single, essentially spherical, galaxy emerges from the chaos. By that point, much of the gas and dust (the fuel for star formation) in this system will have been used up or blown away. ...

Image Credit: ESO/Mahdi Zamani

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Cerro Armazones, in Chile's Atacama Desert, is the site of ESO’s upcoming giant, the Extremely Large Telescope (ELT). In this image, we see the road leading up to this 3000m-high mountain, and in the distance, ESO’s Very Large Telescope (VLT). The lasers of the VLT reach towards the sky, parallel to the Milky Way. Cerro Armazones was actually the first suggested site for the VLT, and now the mountain will finally get a telescope of its own.

Working at high altitude is not easy, but Cerro Armazones is both dry and has almost no artificial light pollution, making it a perfect site with excellent conditions for the world’s biggest eye on the sky. In this picture we see a red shimmer illuminating the dark sky, a natural phenomenon called airglow.

With an anticipated first light later this decade, and equipped with a range of scientific instruments, the ELT will be able to probe the Milky Way and its stars and planets, as well as look back in time to unravel the mysteries of cosmos. One can truly say that good things come to those who wait.

Image Credit: ESA/Hubble & NASA, R. Cohen

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This scintillating image showcases the globular cluster NGC 6540 in the constellation Sagittarius, which was captured by the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3 and Advanced Camera for Surveys. These two instruments have slightly different fields of view — which determines how large an area of sky each instrument captures. This composite image shows the star-studded area of sky that was captured in both instruments’ field of view.

NGC 6540 is a globular cluster, a stable, tightly bound multitude of stars. The populations of these clusters can range from tens of thousands to millions of stars, all of which are trapped in a closely-packed group by their mutual gravitational attraction.

The brightest stars in this image are adorned with prominent cross-shaped patterns of light known as diffraction spikes. These astronomical embellishments are a type of imaging artefact, meaning that they are caused by the structure of Hubble rather than the stars themselves. The path taken by the starlight as it enters the telescope is slightly disturbed by its internal structure, causing bright objects to be surrounded by spikes of light.

Hubble peered into the heart of NGC 6540 to help astronomers measure the ages, shapes, and structures of globular clusters towards the centre of the Milky Way. The gas and dust shrouding the centre of our galaxy block some of the light from these clusters, as well as subtly changing the colours of their stars. Globular clusters contain insights into the earliest history of the Milky Way, and so studying them can help astronomers understand how our galaxy has evolved.