Category Archives: Space Science

ESO: Observation of the birth of a galaxy cluster in early universe

The latest report from the European Southern Observatory (ESO):

Astronomers witness the birth of
a very distant cluster of galaxies from the early Universe

This image shows the protocluster around the Spiderweb galaxy (formally known as MRC 1138-262), seen at a time when the Universe was only 3 billion years old. Most of the mass in the protocluster does not reside in the galaxies that can be seen in the centre of the image, but in the gas known as the intracluster medium (ICM). The hot gas in the ICM is shown as an overlaid blue cloud.  The hot gas was detected with the Atacama Large Millimeter/submillimeter Array (ALMA), of which ESO is a partner. As light from the cosmic microwave background –– the relic radiation from the Big Bang –– travels through the ICM, it gains energy when it interacts with the electrons in the hot gas. This is known as the Sunyaev-Zeldovich effect. By studying this effect, astronomers can infer how much hot gas resides in the ICM, and show that the Spiderweb protocluster is in the process of becoming a massive cluster held together by its own gravity.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), of which ESO is a partner, astronomers have discovered a large reservoir of hot gas in the still-forming galaxy cluster around the Spiderweb galaxy — the most distant detection of such hot gas yet. Galaxy clusters are some of the largest objects known in the Universe and this result, published today in Nature, further reveals just how early these structures begin to form.

Galaxy clusters, as the name suggests, host a large number of galaxies — sometimes even thousands. They also contain a vast “intracluster medium” (ICM) of gas that permeates the space between the galaxies in the cluster. This gas in fact considerably outweighs the galaxies themselves. Much of the physics of galaxy clusters is well understood; however, observations of the earliest phases of formation of the ICM remain scarce.

Previously, the ICM had only been studied in fully-formed nearby galaxy clusters. Detecting the ICM in distant protoclusters — that is, still-forming galaxy clusters – would allow astronomers to catch these clusters in the early stages of formation. A team led by Luca Di Mascolo, first author of the study and researcher at the University of Trieste, Italy, were keen to detect the ICM in a protocluster from the early stages of the Universe.

Galaxy clusters are so massive that they can bring together gas that heats up as it falls towards the cluster.

Cosmological simulations have predicted the presence of hot gas in protoclusters for over a decade, but observational confirmations has been missing,”

explains Elena Rasia, researcher at the Italian National Institute for Astrophysics (INAF) in Trieste, Italy, and co-author of the study.

Pursuing such key observational confirmation led us to carefully select one of the most promising candidate protoclusters.

That was the Spiderweb protocluster, located at an epoch when the Universe was only 3 billion years old. Despite being the most intensively studied protocluster, the presence of the ICM has remained elusive. Finding a large reservoir of hot gas in the Spiderweb protocluster would indicate that the system is on its way to becoming a proper, long-lasting galaxy cluster rather than dispersing.

This image shows the protocluster around the Spiderweb galaxy (formally known as MRC 1138-262). The light that we see in the image shows galaxies at a time when the Universe was only 3 billion years old. Most of the mass in the protocluster does not reside in the galaxies, but in the gas known as the intracluster medium. Because of the mass in the gas, the protocluster is in the process of becoming a massive cluster held together by its own gravity.

Di Mascolo’s team detected the ICM of the Spiderweb protocluster through what’s known as the thermal Sunyaev-Zeldovich (SZ) effect. This effect happens when light from the cosmic microwave background — the relic radiation from the Big Bang — passes through the ICM. When this light interacts with the fast-moving electrons in the hot gas it gains a bit of energy and its colour, or wavelength, changes slightly.

At the right wavelengths, the SZ effect thus appears as a shadowing effect of a galaxy cluster on the cosmic microwave background,”

explains Di Mascolo.

By measuring these shadows on the cosmic microwave background, astronomers can therefore infer the existence of the hot gas, estimate its mass and map its shape.

Thanks to its unparalleled resolution and sensitivity, ALMA is the only facility currently capable of performing such a measurement for the distant progenitors of massive clusters,” says Di Mascolo.

They determined that the Spiderweb protocluster contains a vast reservoir of hot gas at a temperature of a few tens of millions of degrees Celsius. Previously, cold gas had been detected in this protocluster, but the mass of the hot gas found in this new study outweighs it by thousands of times. This finding shows that the Spiderweb protocluster is indeed expected to turn into a massive galaxy cluster in around 10 billion years, growing its mass by at least a factor of ten.

Tony Mroczkowski, co-author of the paper and researcher at ESO, explains that

this system exhibits huge contrasts. The hot thermal component will destroy much of the cold component as the system evolves, and we are witnessing a delicate transition.”

 He concludes that

 “it provides observational confirmation of long-standing theoretical predictions about the formation of the largest gravitationally bound objects in the Universe.

These results help to set the groundwork for synergies between ALMA and ESO’s upcoming Extremely Large Telescope (ELT), which

will revolutionise the study of structures like the Spiderweb,

says Mario Nonino, a co-author of the study and researcher at the Astronomical Observatory of Trieste. The ELT and its state-of-the-art instruments, such as HARMONI and MICADO, will be able to peer into protoclusters and tell us about the galaxies in them in great detail. Together with ALMA’s capabilities to trace the forming ICM, this will provide a crucial glimpse into the assembly of some of the largest structures in the early Universe.


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ESO: Stellar nursery revealed with visible and infrared survey telescope

A new report from the European Southern Observatory (ESO):

Serpent in the sky captured with ESO telescope

This image of the spectacular Sh2-54 nebula was taken in infrared light using ESO’s VISTA telescope at Paranal Observatory in Chile. The clouds of dust and gas that are normally obvious in visible light are less evident here, and in this light we can see the light of the stars behind the nebulae now piercing through. Credit: ESO/VVVX

A myriad of stars is revealed behind the faint orange glow of the Sh2-54 nebula in this new infrared image. Located in the constellation Serpens, this stunning stellar nursery has been captured in all its intricate detail using the Visible and Infrared Survey Telescope for Astronomy (VISTA) based at ESO’s Paranal Observatory in Chile.

When the ancients looked up at the night sky they saw random patterns in the stars. The Greeks, for instance, named one of these “constellations” Serpens, because of its resemblance to a snake. What they wouldn’t have been able to see is that at the tail end of this constellation there is a wealth of stunning astronomical objects. These include the Eagle, the Omega and the Sh2-54 nebulae; the last of these is revealed, in a new light, in this spectacular infrared image.

Nebulae are vast clouds of gas and dust from which stars are born. Telescopes have allowed astronomers to identify and analyse these rather faint objects in exquisite detail. The nebula shown here, located about 6000 light-years away, is officially called Sh2-54; the “Sh” refers to the US astronomer Steward Sharpless, who catalogued more than 300 nebulae in the 1950s.

As the technology used to explore the Universe progresses, so too does our understanding of these stellar nurseries. One of these advances is the ability to look beyond the light that can be detected by our eyes, such as infrared light. Just as the snake, the namesake of this nebula, evolved the ability to sense infrared light to better understand its environment, so too have we developed infrared instruments to learn more about the Universe.

Whilst visible light is easily absorbed by clouds of dust in nebulae, infrared light can pass through the thick layers of dust almost unimpeded. The image here therefore reveals a wealth of stars hidden behind the veils of dust. This is particularly useful as it allows scientists to study what happens in stellar nurseries in much greater detail, and thus learn more about how stars form.

A visible-light image of the Sh2-54 nebula, captured by the VLT Survey Telescope at ESO’s Paranal Observatory in Chile. At these wavelengths the structure of the nebula is clear and the clouds of dust and gas block the light of stars within and behind it. [See side-by-side interactive comparison of Sh2-54 in visible and infrared light] Credit: ESO

This image was captured in infrared light using the sensitive 67-million-pixel camera on ESO’s VISTA telescope at Paranal Observatory in Chile. It was taken as part of the VVVX survey — the VISTA Variables in the Via Láctea eXtended survey. This is a multi-year project that has repeatedly observed a large portion of the Milky Way at infrared wavelengths, providing key data to understand stellar evolution.


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ESO: Distant black hole swallowing a star discovered in visible light

The latest report from the European Southern Observatory (ESO):

Most distant detection of a black hole swallowing a star

This artist’s impression illustrates how it might look when a star approaches too close to a black hole, where the star is squeezed by the intense gravitational pull of the black hole. Some of the star’s material gets pulled in and swirls around the black hole forming the disc that can be seen in this image. In rare cases, such as this one, jets of matter and radiation are shot out from the poles of the black hole. In the case of the AT2022cmc event, evidence of the jets was detected by various telescopes including the VLT, which determined this was the most distant example of such an event.

Earlier this year, the European Southern Observatory’s Very Large Telescope (ESO’s VLT) was alerted after an unusual source of visible light had been detected by a survey telescope. The VLT, together with other telescopes, was swiftly repositioned towards the source: a supermassive black hole in a distant galaxy that had devoured a star, expelling the leftovers in a jet. The VLT determined it to be the furthest example of such an event to have ever been observed. Because the jet is pointing almost towards us, this is also the first time it has been discovered with visible light, providing a new way of detecting these extreme events.

Stars that wander too close to a black hole are ripped apart by the incredible tidal forces of the black hole in what is known as a tidal disruption event (TDE). Approximately 1% of these cause jets of plasma and radiation to be ejected from the poles of the rotating black hole. In 1971, the black hole pioneer John Wheeler[1] introduced the concept of jetted-TDEs as “a tube of toothpaste gripped tight about its middle,” causing the system to “squirt matter out of both ends.

We have only seen a handful of these jetted-TDEs and they remain very exotic and poorly understood events,”

says Nial Tanvir from the University of Leicester in the UK, who led the observations to determine the object’s distance with the VLT. Astronomers are thus constantly hunting for these extreme events to understand how the jets are actually created and why such a small fraction of TDEs produce them.

As part of this quest many telescopes, including the Zwicky Transient Facility (ZTF) in the US, repeatedly survey the sky for signs of short-lived, often extreme, events that could then be studied in much greater detail by telescopes such as ESO’s VLT in Chile.

We developed an open-source data pipeline to store and mine important information from the ZTF survey and alert us about atypical events in real time,”

explains Igor Andreoni, an astronomer at the University of Maryland in the US who co-led the paper published today in Nature together with Michael Coughlin from the University of Minnesota.

In February of this year the ZTF detected a new source of visible light. The event, named AT2022cmc, was reminiscent of a gamma ray burst — the most powerful source of light in the Universe. The prospect of witnessing this rare phenomenon prompted astronomers to trigger several telescopes from across the globe to observe the mystery source in more detail. This included ESO’s VLT, which quickly observed this new event with the X-shooter instrument. The VLT data placed the source at an unprecedented distance for these events: the light produced from AT2022cmc began its journey when the universe was about one third of its current age.

A wide variety of light, from high energy gamma rays to radio waves, was collected by 21 telescopes around the world. The team compared these data with different kinds of known events, from collapsing stars to kilonovae. But the only scenario that matched the data was a rare jetted-TDE pointing towards us. Giorgos Leloudas, an astronomer at DTU Space in Denmark and co-author of this study, explains that

because the relativistic jet is pointing at us, it makes the event much brighter than it would otherwise appear, and visible over a broader span of the electromagnetic spectrum.

The VLT distance measurement found AT2022cmc to be the most distant TDE to have ever been discovered, but this is not the only record-breaking aspect of this object.

Until now, the small number of jetted-TDEs that are known were initially detected using high energy gamma-ray and X-ray telescopes, but this was the first discovery of one during an optical survey,”

says Daniel Perley, an astronomer at Liverpool John Moores University in the UK and co-author of the study. This demonstrates a new way of detecting jetted-TDEs, allowing further study of these rare events and probing of the extreme environments surrounding black holes.


[1] John Archibald Wheeler is also often credited with coining the term ‘black hole’ in a 1967 speech to NASA.


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ESO: Images of the Cone Nebula, an immense star factory

The latest report from the European Southern Observatory (ESO):

ESO images a wondrous star factory to mark 60 years of collaboration

The Cone Nebula is part of a star-forming region of space, NGC 2264, about 2500 light-years away. Its pillar-like appearance is a perfect example of the shapes that can develop in giant clouds of cold molecular gas and dust, known for creating new stars. This dramatic new view of the nebula was captured with the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) instrument on ESO’s Very Large Telescope (VLT), and released on the occasion of ESO’s 60th anniversary.

For the past 60 years the European Southern Observatory (ESO) has been enabling scientists worldwide to discover the secrets of the Universe. We mark this milestone by bringing you a spectacular new image of a star factory, the Cone Nebula, taken with ESO’s Very Large Telescope (VLT).

On 5 October 1962 five countries signed the convention to create ESO. Now, six decades later and supported by 16 Member States and strategic partners, ESO brings together scientists and engineers from across the globe to develop and operate advanced ground-based observatories in Chile that enable breakthrough astronomical discoveries.​

On the occasion of ESO’s 60th anniversary we are releasing this remarkable new image of the Cone Nebula, captured earlier this year with one of ESO’s telescopes and selected by ESO staff. This is part of a campaign marking ESO’s 60th anniversary and taking place in late 2022, both on social media under the #ESO60years hashtag, and with local events in the ESO Member States and other countries.

In this new image, we see centre-stage the seven-light-year-long pillar of the Cone Nebula, which is part of the larger star-forming region NGC 2264 and was discovered in the late 18th century by astronomer William Herschel. In the sky, we find this horn-shaped nebula in the constellation Monoceros (The Unicorn), a surprisingly fitting name.

Located less than 2500 light-years away, the Cone Nebula is relatively close to Earth, making it a well-studied object. But this view is more dramatic than any obtained before, as it showcases the nebula’s dark and impenetrable cloudy appearance in a way that makes it resemble a mythological creature.

This image from the Digitized Sky Survey (DSS) shows the region of the sky around the Cone Nebula. The nebulous area at the centre of the image is NGC 2264, an area of the sky that includes the Christmas Tree star cluster and the Cone Nebula below it (at the very centre of the frame).

The Cone Nebula is a perfect example of the pillar-like shapes that develop in the giant clouds of cold molecular gas and dust, known for creating new stars. This type of pillar arises when massive, newly formed bright blue stars give off stellar winds and intense ultraviolet radiation that blow away the material from their vicinity. As this material is pushed away, the gas and dust further away from the young stars gets compressed into dense, dark and tall pillar-like shapes. This process helps create the dark Cone Nebula, pointing away from the brilliant stars in NGC 2264.

In this image, obtained with the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) on ESO’s VLT in Chile, hydrogen gas is represented in blue and sulphur gas in red. The use of these filters makes the otherwise bright blue stars, that indicate the recent star formation, appear almost golden, contrasting with the dark cone like sparklers.

This image is just one example of the many stunning and awe-inspiring observations ESO telescopes have made in the past 60 years. While this one was obtained for outreach purposes, the overwhelming majority of ESO’s telescope time is dedicated to scientific observations that have allowed us to capture the first image of an exoplanet, study the black hole at the centre of our home galaxy, and find proof that the expansion of our Universe is accelerating.

Building on our 60 years of experience ​in astronomy development, discovery and cooperation, ​ESO continues to chart new territory for astronomy, technology and international collaboration. With our current facilities and ESO’s upcoming Extremely Large Telescope (ELT), we will keep on addressing humanity’s biggest questions about the Universe ​and enabling unimaginable discoveries.​


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ESO: VLT detects heaviest element ever found in an exoplanet atmosphere

A new report from European Southern Observatory (ESO):

Heaviest element yet detected in an exoplanet atmosphere

This artist’s impression shows an ultra-hot exoplanet, a planet beyond our Solar System, as it is about to transit in front of its host star. When the light from the star passes through the planet’s atmosphere, it is filtered by the chemical elements and molecules in the gaseous layer. With sensitive instruments, the signatures of those elements and molecules can be observed from Earth. Using the ESPRESSO instrument of ESO’s Very Large Telescope, astronomers have found the heaviest element yet in an exoplanet’s atmosphere, barium, in the two ultra-hot Jupiters WASP-76 b and WASP-121 b.

Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), astronomers have discovered the heaviest element ever found in an exoplanet atmosphere — barium. They were surprised to discover barium at high altitudes in the atmospheres of the ultra-hot gas giants WASP-76 b and WASP-121 b — two exoplanets, planets which orbit stars outside our Solar System. This unexpected discovery raises questions about what these exotic atmospheres may be like.

“The puzzling and counterintuitive part is: why is there such a heavy element in the upper layers of the atmosphere of these planets?”

says Tomás Azevedo Silva, a PhD student at the University of Porto and the Instituto de Astrofísica e Ciências do Espaço (IA) in Portugal who led the study published today in Astronomy & Astrophysics.

WASP-76 b and WASP-121 b are no ordinary exoplanets. Both are known as ultra-hot Jupiters as they are comparable in size to Jupiter whilst having extremely high surface temperatures soaring above 1000°C. This is due to their close proximity to their host stars, which also means an orbit around each star takes only one to two days. This gives these planets rather exotic features; in WASP-76 b, for example, astronomers suspect it rains iron.

But even so, the scientists were surprised to find barium, which is 2.5 times heavier than iron, in the upper atmospheres of WASP-76 b and WASP-121 b.

“Given the high gravity of the planets, we would expect heavy elements like barium to quickly fall into the lower layers of the atmosphere,”

explains co-author Olivier Demangeon, a researcher also from the University of Porto and IA.

“This was in a way an ‘accidental’ discovery,” says Azevedo Silva. “We were not expecting or looking for barium in particular and had to cross-check that this was actually coming from the planet since it had never been seen in any exoplanet before.”

The fact that barium was detected in the atmospheres of both of these ultra-hot Jupiters suggests that this category of planets might be even stranger than previously thought. Although we do occasionally see barium in our own skies, as the brilliant green colour in fireworks, the question for scientists is what natural process could cause this heavy element to be at such high altitudes in these exoplanets.

​​“At the moment, we are not sure what the mechanisms are,”

explains Demangeon.

This illustration shows a night-side view of the exoplanet WASP-76 b. The ultra-hot giant exoplanet has a day side where temperatures climb above 2400 degrees Celsius, high enough to vaporise metals. Strong winds carry iron vapour to the cooler night side where it condenses into iron droplets. To the left of the image, we see the evening border of the exoplanet, where it transitions from day to night.

In the study of exoplanet atmospheres ultra-hot Jupiters are extremely useful. As Demangeon explains:

“Being gaseous and hot, their atmospheres are very extended and are thus easier to observe and study than those of smaller or cooler planets”.

Determining the composition of an exoplanet’s atmosphere requires very specialised equipment. The team used the ESPRESSO instrument on ESO’s VLT in Chile to analyse starlight that had been filtered through the atmospheres of WASP-76 b and WASP-121 b. This made it possible to clearly detect several elements in them, including barium.

These new results show that we have only scratched the surface of the mysteries of exoplanets. With future instruments such as the high-resolution ArmazoNes high Dispersion Echelle Spectrograph (ANDES), which will operate on ESO’s upcoming Extremely Large Telescope (ELT), astronomers will be able to study the atmospheres of exoplanets large and small, including those of rocky planets similar to Earth, in much greater depth and to gather more clues as to the nature of these strange worlds.


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