Category Archives: Space Science

ESO: Most distant galactic magnetic field detected

A new report from the European Southern Observatory (ESO). Note that the galaxy of interest was initially discovered by a citizen science project sponsored by the BBC’s Stargazing Live television program [1].

Furthest ever detection of a galaxy’s magnetic field

This image shows the orientation of the magnetic field in the distant 9io9 galaxy, seen here when the Universe was only 20% of its current age — the furthest ever detection of a galaxy’s magnetic field. The observations were done with the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner. Dust grains within 9io9 are somewhat aligned with the galaxy’s magnetic field, and due to this they emit polarised light, meaning that light waves oscillate along a preferred direction rather than randomly. ALMA detected this polarisation signal, from which astronomers could work out the orientation of the magnetic field, shown here as curved lines overlaid on the ALMA image. The polarised light signal emitted by the magnetically aligned dust in 9io9 was extremely faint, representing just one percent of the total brightness of the galaxy, so astronomers used a clever trick of nature to help them obtain this result. The team was helped by the fact that 9io9, although very distant from us, had been magnified via a process known as gravitational lensing. This occurs when light from a distant galaxy, in this case 9io9, appears brighter and distorted as it is bent by the gravity of a very large object in the foreground.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), astronomers have detected the magnetic field of a galaxy so far away that its light has taken more than 11 billion years to reach us: we see it as it was when the Universe was just 2.5 billion years old. The result provides astronomers with vital clues about how the magnetic fields of galaxies like our own Milky Way came to be.

Lots of astronomical bodies in the Universe have magnetic fields, whether it be planets, stars or galaxies.

Many people might not be aware that our entire galaxy and other galaxies are laced with magnetic fields, spanning tens of thousands of light-years,”

says James Geach, a professor of astrophysics at the University of Hertfordshire, UK, and lead author of the study published today in Nature.

We actually know very little about how these fields form, despite their being quite fundamental to how galaxies evolve,”

adds Enrique Lopez Rodriguez, a researcher at Stanford University, USA, who also participated in the study. It is not clear how early in the lifetime of the Universe, and how quickly, magnetic fields in galaxies form because so far astronomers have only mapped magnetic fields in galaxies close to us.

Now, using ALMA, in which the European Southern Observatory (ESO) is a partner, Geach and his team have discovered a fully formed magnetic field in a distant galaxy, similar in structure to what is observed in nearby galaxies. The field is about 1000 times weaker than the Earth’s magnetic field, but extends over more than 16 000 light-years.

This discovery gives us new clues as to how galactic-scale magnetic fields are formed,

explains Geach. Observing a fully developed magnetic field this early in the history of the Universe indicates that magnetic fields spanning entire galaxies can form rapidly while young galaxies are still growing.

The team believes that intense star formation in the early Universe could have played a role in accelerating the development of the fields. Moreover, these fields can in turn influence how later generations of stars will form. Co-author and ESO astronomer Rob Ivison says that the discovery opens up

“a new window onto the inner workings of galaxies, because the magnetic fields are linked to the material that is forming new stars.”

To make this detection, the team searched for light emitted by dust grains in a distant galaxy, 9io9 [1]. Galaxies are packed full of dust grains and when a magnetic field is present, the grains tend to align and the light they emit becomes polarised. This means that the light waves oscillate along a preferred direction rather than randomly. When ALMA detected and mapped a polarised signal coming from 9io9, the presence of a magnetic field in a very distant galaxy was confirmed for the first time.

No other telescope could have achieved this,”

says Geach. The hope is that with this and future observations of distant magnetic fields the mystery of how these fundamental galactic features form will begin to unravel.


[1] 9io9 was discovered in the course of a citizen science project. The discovery was helped by viewers of the British BBC television programme Stargazing Live, when over three nights in 2014 the audience was asked to examine millions of images in the hunt for distant galaxies.


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ESO: Explaining the ups and downs in a pulsar’s brightness

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

ESO telescopes help unravel pulsar puzzle

This artist’s impression shows the pulsar PSR J1023+0038 stealing gas from its companion star. This gas accumulates in a disc around the pulsar, slowly falls towards it, and is eventually expelled in a narrow jet. In addition, there is a wind of particles blowing away from the pulsar, represented here by a cloud of very small dots. This wind clashes with the infalling gas, heating it up and making the system glow brightly in X-rays and ultraviolet and visible light. Eventually, blobs of this hot gas are expelled along the jet, and the pulsar returns to the initial, fainter state, repeating the cycle. This pulsar has been observed to switch incessantly between these two states every few seconds or minutes.

With a remarkable observational campaign that involved 12 telescopes both on the ground and in space, including three European Southern Observatory (ESO) facilities, astronomers have uncovered the strange behaviour of a pulsar, a super-fast-spinning dead star. This mysterious object is known to switch between two brightness modes almost constantly, something that until now has been an enigma. But astronomers have now found that sudden ejections of matter from the pulsar over very short periods are responsible for the peculiar switches.

“We have witnessed extraordinary cosmic events where enormous amounts of matter, similar to cosmic cannonballs, are launched into space within a very brief time span of tens of seconds from a small, dense celestial object rotating at incredibly high speeds,”

says Maria Cristina Baglio, researcher at New York University Abu Dhabi, affiliated with the Italian National Institute for Astrophysics (INAF), and the lead author of the paper published today in Astronomy & Astrophysics.

A pulsar is a fast-rotating, magnetic, dead star that emits a beam of electromagnetic radiation into space. As it rotates, this beam sweeps across the cosmos — much like a lighthouse beam scanning its surroundings — and is detected by astronomers as it intersects the line of sight to Earth. This makes the star appear to pulse in brightness as seen from our planet.

PSR J1023+0038, or J1023 for short, is a special type of pulsar with a bizarre behaviour. Located about 4500 light-years away in the Sextans constellation, it closely orbits another star. Over the past decade, the pulsar has been actively pulling matter off this companion, which accumulates in a disc around the pulsar and slowly falls towards it.

Since this process of accumulating matter began, the sweeping beam virtually vanished and the pulsar started incessantly switching between two modes. In the ‘high’ mode, the pulsar gives off bright X-rays, ultraviolet and visible light, while in the ‘low’ mode it’s dimmer at these frequencies and emits more radio waves. The pulsar can stay in each mode for several seconds or minutes, and then switch to the other mode in just a few seconds. This switching has thus far puzzled astronomers.

“Our unprecedented observing campaign to understand this pulsar’s behaviour involved a dozen cutting-edge ground-based and space-borne telescopes,”

says Francesco Coti Zelati, a researcher at the Institute of Space Sciences, Barcelona, Spain, and co-lead author of the paper. The campaign included ESO’s Very Large Telescope (VLT) and ESO’s New Technology Telescope (NTT), which detected visible and near-infrared light, as well as the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner. Over two nights in June 2021, they observed the system make over 280 switches between its high and low modes.

“We have discovered that the mode switching stems from an intricate interplay between the pulsar wind, a flow of high-energy particles blowing away from the pulsar, and matter flowing towards the pulsar,”

says Coti Zelati, who is also affiliated with INAF.

In the low mode, matter flowing towards the pulsar is expelled in a narrow jet perpendicular to the disc. Gradually, this matter accumulates closer and closer to the pulsar and, as this happens, it is hit by the wind blowing from the pulsating star, causing the matter to heat up. The system is now in a high mode, glowing brightly in the X-ray, ultraviolet and visible light. Eventually, blobs of this hot matter are removed by the pulsar via the jet. With less hot matter in the disc, the system glows less brightly, switching back into the low mode.

While this discovery has unlocked the mystery of J1023’s strange behaviour, astronomers still have much to learn from studying this unique system and ESO’s telescopes will continue to help astronomers observe this peculiar pulsar. In particular, ESO’s Extremely Large Telescope (ELT), currently under construction in Chile, will offer an unprecedented view of J1023’s switching mechanisms.

“The ELT will allow us to gain key insights into how the abundance, distribution, dynamics, and energetics of the inflowing matter around the pulsar are affected by the mode switching behavior,”

concludes Sergio Campana, Research Director at the INAF Brera Observatory and coauthor of the study.


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ESO: Dark spot on Neptune observed by telescope on Earth for first time

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

Mysterious Neptune dark spot detected from Earth for the first time

This image shows Neptune observed with the MUSE instrument at ESO’s Very Large Telescope (VLT). At each pixel within Neptune, MUSE splits the incoming light into its constituent colours or wavelengths. This is similar to obtaining images at thousands of different wavelengths all at once, which provides a wealth of valuable information to astronomers. The image to the right combines all colours captured by MUSE into a “natural” view of Neptune, where a dark spot can be seen to the upper-right. Then we see images at specific wavelengths: 551 nanometres (blue), 831 nm (green), and 848 nm (red); note that the colours are only indicative, for display purposes. The dark spot is most prominent at shorter (bluer) wavelengths. Right next to this dark spot MUSE also captured a small bright one, seen here only in the middle image at 831 nm and located deep in the atmosphere. This type of deep bright cloud had never been identified before on the planet. The images also show several other shallower bright spots towards the bottom-left edge of Neptune, seen at long wavelengths. Imaging Neptune’s dark spot from the ground was only possible thanks to the VLT’s Adaptive Optics Facility, which corrects the blur caused by atmospheric turbulence and allows MUSE to obtain crystal clear images. To better highlight the subtle dark and bright features on the planet, the astronomers carefully processed the MUSE data, obtaining what you see here.

Using ESO’s Very Large Telescope (VLT), astronomers have observed a large dark spot in Neptune’s atmosphere, with an unexpected smaller bright spot adjacent to it. This is the first time a dark spot on the planet has ever been observed with a telescope on Earth. These occasional features in the blue background of Neptune’s atmosphere are a mystery to astronomers, and the new results provide further clues as to their nature and origin.

Large spots are common features in the atmospheres of giant planets, the most famous being Jupiter’s Great Red Spot. On Neptune, a dark spot was first discovered by NASA’s Voyager 2 in 1989, before disappearing a few years later.

Since the first discovery of a dark spot, I’ve always wondered what these short-lived and elusive dark features are,”

says Patrick Irwin, Professor at the University of Oxford in the UK and lead investigator of the study published today in Nature Astronomy.

Irwin and his team used data from ESO’s VLT to rule out the possibility that dark spots are caused by a ‘clearing’ in the clouds. The new observations indicate instead that dark spots are likely the result of air particles darkening in a layer below the main visible haze layer, as ices and hazes mix in Neptune’s atmosphere.

Coming to this conclusion was no easy feat because dark spots are not permanent features of Neptune’s atmosphere and astronomers had never before been able to study them in sufficient detail. The opportunity came after the NASA/ESA Hubble Space Telescope discovered several dark spots in Neptune’s atmosphere, including one in the planet’s northern hemisphere first noticed in 2018. Irwin and his team immediately got to work studying it from the ground — with an instrument that is ideally suited to these challenging observations.

Using the VLT’s Multi Unit Spectroscopic Explorer (MUSE), the researchers were able to split reflected sunlight from Neptune and its spot into its component colours, or wavelengths, and obtain a 3D spectrum [1]. This meant they could study the spot in more detail than was possible before.

I’m absolutely thrilled to have been able to not only make the first detection of a dark spot from the ground, but also record for the very first time a reflection spectrum of such a feature,

says Irwin.

This image shows Neptune observed with the MUSE instrument at ESO’s Very Large Telescope. At each pixel within Neptune, MUSE splits the incoming light into its constituent colours or wavelengths. This is similar to obtaining images at thousands of different wavelengths all at once, which provides a wealth of valuable information to astronomers. This image combines all colours captured by MUSE into a “natural” view of Neptune, where a dark spot can be seen to the upper-right.

Since different wavelengths probe different depths in Neptune’s atmosphere, having a spectrum enabled astronomers to better determine the height at which the dark spot sits in the planet’s atmosphere. The spectrum also provided information on the chemical composition of the different layers of the atmosphere, which gave the team clues as to why the spot appeared dark.

The observations also offered up a surprise result.

In the process we discovered a rare deep bright cloud type that had never been identified before, even from space,”

says study co-author Michael Wong, a researcher at the University of California, Berkeley, USA. This rare cloud type appeared as a bright spot right beside the larger main dark spot, the VLT data showing that the new ‘deep bright cloud’ was at the same level in the atmosphere as the main dark spot. This means it is a completely new type of feature compared to the small ‘companion’ clouds of high-altitude methane ice that have been previously observed.

With the help of ESO’s VLT, it is now possible for astronomers to study features like these spots from Earth. “This is an astounding increase in humanity’s ability to observe the cosmos.

At first, we could only detect these spots by sending a spacecraft there, like Voyager. Then we gained the ability to make them out remotely with Hubble. Finally, technology has advanced to enable this from the ground,

concludes Wong, before adding, jokingly:

This could put me out of work as a Hubble observer!


[1] MUSE is a 3D spectrograph that allows astronomers to observe the entirety of an astronomical object, like Neptune, in one go. At each pixel, the instrument measures the intensity of light as a function of its colour or wavelength. The resulting data form a 3D set in which each pixel of the image has a full spectrum of light. In total, MUSE measures over 3500 colours. The instrument is designed to take advantage of adaptive optics, which corrects for the turbulence in the Earth’s atmosphere, resulting in sharper images than otherwise possible. Without this combination of features, studying a Neptune dark spot from the ground would not have been possible.

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ESO: New type star may help explain magnetars

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

New type of star gives clues to mysterious origin of magnetars

Magnetars are the strongest magnets in the Universe. These super-dense dead stars with ultra-strong magnetic fields can be found all over our galaxy but astronomers don’t know exactly how they form. Now, using multiple telescopes around the world, including European Southern Observatory (ESO) facilities, researchers have uncovered a living star that is likely to become a magnetar. This finding marks the discovery of a new type of astronomical object — massive magnetic helium stars — and sheds light on the origin of magnetars.

Despite having been observed for over 100 years, the enigmatic nature of the star HD 45166 could not be easily explained by conventional models, and little was known about it beyond the fact that it is one of a pair of stars [1], is rich in helium and is a few times more massive than our Sun.

This star became a bit of an obsession of mine,”

says Tomer Shenar, the lead author of a study on this object published today in Science and an astronomer at the University of Amsterdam, the Netherlands.

Tomer and I refer to HD 45166 as the ‘zombie star,”

says co-author and ESO astronomer Julia Bodensteiner, based in Germany.

This is not only because this star is so unique, but also because I jokingly said that it turns Tomer into a zombie.

Having studied similar helium-rich stars before, Shenar thought magnetic fields could crack the case. Indeed, magnetic fields are known to influence the behaviour of stars and could explain why traditional models failed to describe HD 45166, which is located about 3000 light-years away in the constellation Monoceros.

I remember having a Eureka moment while reading the literature: ‘What if the star is magnetic?’,

says Shenar, who is currently based at the Centre for Astrobiology in Madrid, Spain.

Shenar and his team set out to study the star using multiple facilities around the globe. The main observations were conducted in February 2022 using an instrument on the Canada-France-Hawaii Telescope that can detect and measure magnetic fields. The team also relied on key archive data taken with the Fiber-fed Extended Range Optical Spectrograph (FEROS) at ESO’s La Silla Observatory in Chile.

Once the observations were in, Shenar asked co-author Gregg Wade, an expert on magnetic fields in stars at the Royal Military College of Canada, to examine the data. Wade’s response confirmed Shenar’s hunch:

Well my friend, whatever this thing is — it is definitely magnetic.

Shenar’s team had found that the star has an incredibly strong magnetic field, of 43 000 gauss, making HD 45166 the most magnetic massive star found to date [2].

The entire surface of the helium star is as magnetic as the strongest human-made magnets,

explains co-author Pablo Marchant, an astronomer at KU Leuven’s Institute of Astronomy in Belgium.

This observation marks the discovery of the very first massive magnetic helium star.

It is exciting to uncover a new type of astronomical object,” says Shenar, ”especially when it’s been hiding in plain sight all along.

Moreover, it provides clues to the origin of magnetars, compact dead stars laced with magnetic fields at least a billion times stronger than the one in HD 45166. The team’s calculations suggest that this star will end its life as a magnetar. As it collapses under its own gravity, its magnetic field will strengthen, and the star will eventually become a very compact core with a magnetic field of around 100 trillion gauss [3] — the most powerful type of magnet in the Universe.

Shenar and his team also found that HD 45166 has a mass smaller than previously reported, around twice the mass of the Sun, and that its stellar pair orbits at a far larger distance than believed before. Furthermore, their research indicates that HD 45166 formed through the merger of two smaller helium-rich stars.

Our findings completely reshape our understanding of HD 45166,”

concludes Bodensteiner.


[1] While HD 45166 is a binary system, in this text HD 45166 refers to the helium-rich star, not to both stars.

[2] The magnetic field of 43 000 gauss is the strongest magnetic field ever detected in a star that exceeds the Chandrasekhar mass limit, which is the critical limit above which stars may collapse into neutron stars (magnetars are a type of neutron star).

[3] In this text, a billion refers to one followed by nine zeros and a trillion refers to one followed by 12 zeros.

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ESO: Observation of distant gas clouds formed from the first stars

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

Astronomers find distant gas clouds
with leftovers of the first stars

This artist’s impression shows a distant gas cloud that contains different chemical elements, illustrated here with schematic representations of various atoms. Using ESO’s Very Large Telescope, astronomers have detected three distant gas clouds whose chemical composition matches what we expect from the explosions of the first stars that appeared in the Universe. These early stars can be studied indirectly by analysing the chemical elements they dispersed into the surrounding environment after they died in supernova explosions. The three distant gas clouds detected in this study are rich in carbon, oxygen, and magnesium, but poor in iron. This is exactly the signature expected from the explosions of the first stars.

Using ESO’s Very Large Telescope (VLT), researchers have found for the first time the fingerprints left by the explosion of the first stars in the Universe. They detected three distant gas clouds whose chemical composition matches what we expect from the first stellar explosions. These findings bring us one step closer to understanding the nature of the first stars that formed after the Big Bang.

For the first time ever, we were able to identify the chemical traces of the explosions of the first stars in very distant gas clouds,”

says Andrea Saccardi, a PhD student at the Observatoire de Paris – PSL, who led this study during his master’s thesis at the University of Florence.

Researchers think that the first stars that formed in the Universe were very different from the ones we see today. When they appeared 13.5 billion years ago, they contained just hydrogen and helium, the simplest chemical elements in nature [1]. These stars, thought to be tens or hundreds of times more massive than our Sun, quickly died in powerful explosions known as supernovae, enriching the surrounding gas with heavier elements for the first time. Later generations of stars were born out of that enriched gas, and in turn ejected heavier elements as they too died. But the very first stars are now long gone, so how can researchers learn more about them?

Primordial stars can be studied indirectly by detecting the chemical elements they dispersed in their environment after their death,”

says Stefania Salvadori, Associate Professor at the University of Florence and co-author of the study published today in the Astrophysical Journal.

Using data taken with ESO’s VLT in Chile, the team found three very distant gas clouds, seen when the Universe was just 10–15% of its current age, and with a chemical fingerprint matching what we expect from the explosions of the first stars. Depending on the mass of these early stars and the energy of their explosions, these first supernovae released different chemical elements such as carbon, oxygen and magnesium, which are present in the outer layers of stars. But some of these explosions were not energetic enough to expel heavier elements like iron, which is found only in the cores of stars. To search for the telltale sign of these very first stars that exploded as low energy supernovae, the team therefore looked for distant gas clouds poor in iron but rich in the other elements. And they found just that: three faraway clouds in the early Universe with very little iron but plenty of carbon and other elements — the fingerprint of the explosions of the very first stars.

This peculiar chemical composition has also been observed in many old stars in our own galaxy, which researchers consider to be second-generation stars that formed directly from the ‘ashes’ of the first ones. This new study has found such ashes in the early Universe, thus adding a missing piece to this puzzle.

Our discovery opens new avenues to indirectly study the nature of the first stars, fully complementing studies of stars in our galaxy,”

explains Salvadori.

This diagram illustrates how astronomers can analyse the chemical composition of distant clouds of gas using the light of a background object like a quasar as a beacon.   When the light of the quasar passes through the gas cloud, the chemical elements in it absorb different colours or wavelengths, leaving dark lines in the spectrum of the quasar. Each element leaves a different set of lines, so by studying the spectrum astronomers can work out the chemical composition of the intervening gas cloud.

To detect and study these distant gas clouds, the team used light beacons known as quasars — very bright sources powered by supermassive black holes at the centres of faraway galaxies. As the light from a quasar travels through the Universe, it passes through gas clouds where different chemical elements leave an imprint on the light.

To find these chemical imprints, the team analysed data on several quasars observed with the X-shooter instrument on ESO’s VLT. X-shooter splits light into an extremely wide range of wavelengths, or colours, which makes it a unique instrument with which to identify many different chemical elements in these distant clouds.

This study opens new windows for next generation telescopes and instruments, like ESO’s upcoming Extremely Large Telescope (ELT) and its high-resolution ArmazoNes high Dispersion Echelle Spectrograph (ANDES).

With ANDES at the ELT we will be able to study many of these rare gas clouds in greater detail, and we will be able to finally uncover the mysterious nature of the first stars,”

concludes Valentina D’Odorico, a researcher at the National Institute of Astrophysics in Italy and co-author of the study.


[1] Minutes after the Big Bang the only elements present in the Universe were the three lightest ones: hydrogen, helium and very small traces of lithium. Heavier elements were formed much later on in stars.


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An Infinity of Worlds:
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