Three’s a crowd

(130) Elektra
Credit: ESO/Berdeu et al., Yang et al.

Between Mars and Jupiter lie some of the relics of the early Solar System: the main asteroid belt. This belt is full of unusual asteroids whose origins reveal the building blocks of the early terrestrial planets. Of these, one of the more intriguing is Elektra, imaged here using the instrument SPHERE, installed on ESO’s Very Large Telescope at Paranal, Chile. 

Previously, Elektra was known to have not one but two moons orbiting it, shown by the orange and green orbits respectively. But now a team of astronomers, led by Anthony Berdeu, from the National Astronomical Research Institute of Thailand, have found a new satellite orbiting the asteroid — shown with the blue orbit. This discovery makes Elektra the first ever quadruple asteroid system.

This new, third moonlet of Elektra, provisionally named S/2014 (130) 2, lies closer to its parent asteroid than the other moons, at an average distance just under 350 km, and is 15000 times fainter than Elektra. The team used public data from the ESO science archive and a new processing technique to reveal this small moon. The discovery will help astronomers understand how these satellites form and, in turn, provides crucial information about planetary formation and evolution of our own solar system.

SPHERE, the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument, is a powerful planet-finding instrument. It uses an extreme adaptive optics system which allows for real time corrections of turbulence in the Earth’s atmosphere which causes stars to twinkle. It was only with SPHERE’s sensitivity and spatial resolution, coupled with cutting-edge data processing techniques, that the team was able to spot Elektra’s newest satellite.

Link

• Video showing the asteroid and its moons in motion
• Three's a crowd (non-annotated)

Source: ESO/potw

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A Galaxy Far, Far, Away: Cosmic Behemoths, and their Origins

Artist impression of the 14 galaxies detected by ALMA as they appear in the very early, very distant universe. These galaxies are in the process of merging and will eventually form the core of a massive galaxy cluster.

A century ago two prominent astronomers held a debate at the Smithsonian Museum of Natural History. The topic concerned the nature of the faint spiral nebulae seen in the night sky—are they galaxies that each contain billions of stars like our own Milky Way, or are they found within the Milky Way itself? The answer to this question would have profound implications for the size of our universe. We now know that these nebulae are indeed separate galaxies, but we still don’t fully understand how they form and evolve. It is a question the Next Generation Very Large Array (ngVLA) will help us understand. The ngVLA will study galaxy evolution by comparing how the fuel available for making stars matches up with the rate at which they are formed throughout the history of the cosmos.

Stars are born in stellar nurseries swaddled in enormous clouds of gas. The coldest, densest clouds of gas collapse under gravity, until enough material is pulled together in one spot to form a star, or multiple stars, in several parts of the cloud. But nature provides challenges to star formation. For example, powerful jets can shoot out during the process of star formation and push back on the collapsing gas clouds against gravity. Furthermore, baby stars themselves emit hot radiation that can act to evaporate the surrounding gas. Understanding the fine-tuned balance between these different competing phenomena in galaxies is a major goal of the ngVLA, primarily by looking at the cold gas itself rather than the end product of the whole process. This will be important for scientists to evaluate if their models of the star formation process correctly describe what happens in reality inside our cosmic neighbors, and in the universe beyond.

Tracing the cold gas content of galaxies throughout cosmic history is key to understanding how the stars and planetary systems we find in galaxies today were originally made, and thus, how galaxy evolution takes place. This evolution began only a few hundred million years after the Big Bang (i.e., more than 13 billion years ago) when galaxies first formed. In a single day of observations, the ngVLA will find tens to hundreds of galaxies in the early Universe based on the emission from the star-forming gas within them, while at the same time mapping the distribution and motion of the gas down to the size scales of individual star-forming clouds. Enabled by broad support in the US and from the worldwide astronomical community, these studies will transform our understanding of galaxy formation and evolution across cosmic history in the coming decade.

By Daniel Dale*

*Daniel Dale is the Harry C. Vaughan Professor of Astronomy at the University of Wyoming, where he studies star formation in nearby galaxies.

Source: National Radio Astronomy Observatory (NRAO)/Blogs

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Surprisingly High Fraction of Dead Galaxies Found in Ancient Galactic City

Four of the 38 galaxies in the protocluster MAGAZ3N3 J095924+022537 that were imaged using keck observatoryʻs mosfire instrument.Credit: I. McConachie, G. Wilson/UC Riverside

Why Cluster’s Galaxies are Unlike Those in All the Other Known Protoclusters is a Mystery, says UC Riverside-led Team

Maunakea, Hawaiʻi – An international team of astronomers led by researchers at the University of California, Riverside (UCR), has discovered a massive cluster of young galaxies forming in the early universe.

With the help of W. M. Keck Observatory on Maunakea, Hawaiʻi Island, the team found that the newly discovered growing galactic metropolis, named MAGAZ3NE J095924+022537, is a newborn galaxy cluster, or protocluster, consisting of at least 38 member galaxies, and is about 11.8 billion light-years away from Earth.

Galaxy clusters grow over time under gravity and, in the present-day universe, can contain hundreds or even thousands of galaxies, as well as hot gas and dark matter. As time goes by, their galaxies burn through the fuel available and evolve from vigorously star-forming galaxies into red and dead galaxies.

“In the early universe, all protoclusters discovered until now are full of vigorously star-forming galaxies,” said Ian McConachie, a graduate student in the UCR Department of Physics and Astronomy and the lead author of the research paper published in The Astrophysical Journal. “But incredibly, unlike all of the other protoclusters that have been found at this epoch, many galaxies in MAGAZ3NE J0959 appear to have already stopped forming stars.”

“We were surprised to find a galaxy graveyard in such a young cluster,” said co-author Percy Gomez, a staff astronomer at Keck Observatory who worked with and mentored McConachie during his time as a Keck Visiting Scholar. “Now the question is, what did these galaxies look like before? A new search is on.”

Co-author Gillian Wilson, a professor of physics and astronomy at UCR in whose lab McConachie works, said J0959 was discovered from the “Massive Ancient Galaxies At Z > 3 NEar-infrared,” or MAGAZ3NE, survey, designed to discover and study ultramassive galaxies and their neighbors.

“We are seeing this protocluster as it appeared when the universe was less than 2 billion years old,” she said. “It is as if you took a cluster like Coma, the nearest rich cluster of galaxies to Earth, and plopped it into the early universe.”

In the early universe, all previously discovered distant protoclusters like, for example, “The Spiderweb” (left: artist’s impression) are full of vigorously star-forming galaxies. In contrast, the newly-discovered protocluster “MAGAZ3NE J095924+022537” contains a high fraction of red and dead galaxies like the nearby “Coma” cluster (right). The discovery of an ancient cluster containing galaxies which resemble those found in modern clusters was a huge surprise. Credits: Spiderweb: M. Kornmesser/ESO; Coma: Russ Carroll, Robert Gendler, & Bob Franke/Dan Zowada Memorial ObservaItory. 

Co-author Benjamin Forrest, a former postdoctoral researcher in Wilson’s lab who is now based at UC Davis, explained that at the heart of MAGAZ3NE J0959 is an ultramassive galaxy that has already formed a mass of more than 200 billion suns.

“Why this ultramassive galaxy and so many of its neighbors formed most of their stars and then became inactive when the universe was still so young, in contrast to other known protoclusters from the same time, is a big mystery,” he said. “Why its galaxies are so unlike those in all the other known protoclusters, and so similar to those in Coma, is a complete mystery.”

Forrest added that MAGAZ3NE J0959 was discovered from the ground, but the advent of powerful new capabilities, like the recently-launched James Webb Space Telescope, should soon reveal whether there are other protoclusters like MAGAZ3NE J0959 packed with dead galaxies waiting to be found in the early universe.

“Should such protoclusters be found in large numbers, it would mean that the current paradigm of protocluster formation would require a major revision,” Forrest said. “A new scenario of protoclusters existing in a diversity of states in the early universe would have to be adopted. With many member galaxies quenching in the first two billion years, this would almost certainly pose significant challenges for current models of galaxy simulation.”

The team used spectroscopic observations from Keck Observatory’s Multi-Object Spectrograph for Infrared Exploration, or MOSFIRE, to make detailed measurements of MAGAZ3NE J0959 and precisely quantify its distances.

Closely associated to the question of how ultramassive galaxies form is the question of the environment in which they form, for example, are they always found in overdense environments like protoclusters, or can they also form in isolation? Next, the team plans to study the neighborhood of all other ultramassive galaxies in the MAGAZ3NE survey to answer this question.

The study was supported by grants from the National Science Foundation and NASA.

Source: W.M.Keck Observatory

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About MOSFIRE

The Multi-Object Spectrograph for Infrared Exploration (MOSFIRE), gathers thousands of spectra from objects spanning a variety of distances, environments and physical conditions. What makes this large, vacuum-cryogenic instrument unique is its ability to select up to 46 individual objects in the field of view and then record the infrared spectrum of all 46 objects simultaneously. When a new field is selected, a robotic mechanism inside the vacuum chamber reconfigures the distribution of tiny slits in the focal plane in under six minutes. Eight years in the making with First Light in 2012, MOSFIRE’s early performance results range from the discovery of ultra-cool, nearby substellar mass objects, to the detection of oxygen in young galaxies only two billion years after the Big Bang. MOSFIRE was made possible by funding provided by the National Science Foundation.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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New planet detected around star closest to the Sun

PR Image eso2202a

Artist’s impression of Proxima d (close-up) 

 

PR Image eso2202b

Artist’s impression of Proxima d (wider view)

 

PR Image eso2202c

Proxima Centauri in the southern constellation of Centaurus

 

PR Image eso2202d

The sky around Alpha Centauri and Proxima Centauri (annotated)

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Videos

PR Video eso2202a

Ultralight Planet Found Next Door (ESOcast 250 Light)

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A team of astronomers using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile have found evidence of another planet orbiting Proxima Centauri, the closest star to our Solar System. This candidate planet is the third detected in the system and the lightest yet discovered orbiting this star. At just a quarter of Earth’s mass, the planet is also one of the lightest exoplanets ever found.

“The discovery shows that our closest stellar neighbour seems to be packed with interesting new worlds, within reach of further study and future exploration,” explains João Faria, a researcher at the Instituto de Astrofísica e Ciências do Espaço, Portugal and lead author of the study published today in Astronomy & Astrophysics. Proxima Centauri is the closest star to the Sun, lying just over four light-years away.

The newly discovered planet, named Proxima d, orbits Proxima Centauri at a distance of about four million kilometres, less than a tenth of Mercury’s distance from the Sun. It orbits between the star and the habitable zone — the area around a star where liquid water can exist at the surface of a planet — and takes just five days to complete one orbit around Proxima Centauri.

The star is already known to host two other planets: Proxima b, a planet with a mass comparable to that of Earth that orbits the star every 11 days and is within the habitable zone, and candidate Proxima c, which is on a longer five-year orbit around the star.

Proxima b was discovered a few years ago using the HARPS instrument on ESO’s 3.6-metre telescope. The discovery was confirmed in 2020 when scientists observed the Proxima system with a new instrument on ESO’s VLT that had greater precision, the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO). It was during these more recent VLT observations that astronomers spotted the first hints of a signal corresponding to an object with a five-day orbit. As the signal was so weak, the team had to conduct follow-up observations with ESPRESSO to confirm that it was due to a planet, and not simply a result of changes in the star itself.

“After obtaining new observations, we were able to confirm this signal as a new planet candidate,” Faria says. “I was excited by the challenge of detecting such a small signal and, by doing so, discovering an exoplanet so close to Earth.”  

At just a quarter of the mass of Earth, Proxima d is the lightest exoplanet ever measured using the radial velocity technique, surpassing a planet recently discovered in the L 98-59 planetary system. The technique works by picking up tiny wobbles in the motion of a star created by an orbiting planet’s gravitational pull. The effect of Proxima d’s gravity is so small that it only causes Proxima Centauri to move back and forth at around 40 centimetres per second (1.44 kilometres per hour).

“This achievement is extremely important,” says Pedro Figueira, ESPRESSO instrument scientist at ESO in Chile. “It shows that the radial velocity technique has the potential to unveil a population of light planets, like our own, that are expected to be the most abundant in our galaxy and that can potentially host life as we know it.”

“This result clearly shows what ESPRESSO is capable of and makes me wonder about what it will be able to find in the future,” Faria adds.

ESPRESSO’s search for other worlds will be complemented by ESO’s Extremely Large Telescope (ELT), currently under construction in the Atacama Desert, which will be crucial to discovering and studying many more planets around nearby stars.

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More Information

This research was presented in the paper “A candidate short-period sub-Earth orbiting Proxima Centauri” (doi:10.1051/0004-6361/202142337) to appear in Astronomy & Astrophysics.

The team is composed of J. P. Faria (Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Portugal [IA/UPorto], Centro de Astrofísica da Universidade do Porto, Portugal [CAUP] and Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Portugal [FCUP]), A. Suárez Mascareño (Instituto de Astrofísica de Canarias, Tenerife, Spain [IAC], Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain [IAC-ULL]), P. Figueira (European Southern Observatory, Santiago, Chile [ESO-Chile], IA-Porto), A. M. Silva (IA-Porto, FCUP) M. Damasso (Osservatorio Astrofisico di Torino, Italy [INAF-Turin]), O. Demangeon (IA-Porto, FCUP), F. Pepe (Département d’astronomie de l’Université de Genève, Switzerland [UNIGE]), N. C. Santos (IA-Porto, FCUP), R. Rebolo (Consejo Superior de Investigaciones Científicas, Madrid, Spain [CSIC], IAC-ULL, IAC), S. Cristiani (INAF - Osservatorio Astronomico di Trieste, Italy [OATS]), V. Adibekyan (IA-Porto), Y. Alibert (Physics Institute of University of Bern, Switzerland), R. Allart (Department of Physics, and Institute for Research on Exoplanets, Université de Montréal,Canada, UNIGE), S. C. C. Barros (IA-Porto, FCUP), A. Cabral (Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências da Universidade de Lisboa, Portugal [IA-Lisboa], Faculdade de Ciências da Universidade de Lisboa, Portugal [FCUL]), V. D’Odorico (OATS, Institute for Fundamental Physics of the Universe, Trieste, Italy [IFPU], Scuola Normale Superiore, Pisa, Italy) P. Di Marcantonio (OATS), X. Dumusque (UNIGE), D. Ehrenreich (UNIGE), J. I. González Hernández (IAC-ULL, IAC), N. Hara (UNIGE), J. Lillo-Box (Centro de Astrobiología (CAB, CSIC-INTA), Depto. de Astrofísica, Madrid, Spain), G. Lo Curto (European Southern Observatory, Garching bei München, Germany [ESO], ESO-Chile) C. Lovis (UNIGE), C. J. A. P. Martins (IA-Porto, Centro de Astrofísica da Universidade do Porto, Portugal), D. Mégevand (UNIGE), A. Mehner (ESO-Chile), G. Micela (INAF - Osservatorio Astronomico di Palermo, Italy), P. Molaro (OATS), IFPU), N. J. Nunes (IA-Lisboa), E. Pallé (IAC, IAC-ULL), E. Poretti (INAF - Osservatorio Astronomico di Brera, Merate, Italy ), S. G. Sousa (IA-Porto, FCUP), A. Sozzetti (INAF-Turin), H. Tabernero (Centro de Astrobiología, Madrid, Spain [CSIC-INTA]), S. Udry (UNIGE), and M. R. Zapatero Osorio (CSIC-INTA).

The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration in astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates APEX and ALMA on Chajnantor, two facilities that observe the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society.

 

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Links

• Research paper
• Photos of the VLT
• Find out more about ESO's Extremely Large Telescope
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• For scientists: got a story? Pitch your research
  

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Contacts:

João Faria
Instituto de Astrofisica e Ciências do Espaço, Faculdade de Ciências, Universidade do Porto
Porto, Portugal
Tel: +351 226 089 855
Email: joao.faria@astro.up.pt

Pedro Figueira
ESO and Instituto de Astrofísica e Ciências do Espaço
Santiago, Chile
Tel: +56 2 2463 3074
Email: pedro.figueira@eso.org

Nuno Santos
Instituto de Astrofisica e Ciências do Espaço, Faculdade de Ciências, Universidade do Porto
Porto, Portugal
Email: nuno.santos@astro.up.pt

Mario Damasso
INAF – Osservatorio Astrofisico di Torino
Turin, Italy
Tel: +39 339 1816786
Email: mario.damasso@inaf.it

Alejandro Suárez Mascareño
Instituto de Astrofísica de Canarias
Tenerife, Spain
Tel: +34 658 778 954
Email: asm@iac.es

Baptiste Lavie
Département d’astronomie de l’Université de Genève
Genève, Switzerland
Tel: +41 22 379 24 88
Email: baptiste.lavie@unige.ch

Bárbara Ferreira
ESO Media Manager
Garching bei München, Germany
Tel: +49 89 3200 6670
Cell: +49 151 241 664 00
Email: press@eso.org

Source:  ESO/News

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A black hole caught blowing a gust

NGC 7582
Credit: ESO / Juneau et al.

Lurking about 70 million light years away from Earth in the constellation Grus, you will find the galaxy NGC 7582 — a spiral galaxy harbouring a supermassive black hole at its core. These images were captured as part of a study using the MUSE instrument on ESO’s Very Large Telescope (VLT) to uncover the effect of an active black hole on the formation of stars in the galaxy.

The galaxy contains an active galactic nucleus (AGN)  — an extremely energetic central engine powered by the supermassive black hole gobbling up material in its immediate surroundings.  Matter heats up in this process, launching huge amounts of energy and powerful winds into the surrounding area. But what effect does this have on the galaxy at large? 

To find out, a recent study, led by Stéphanie Juneau from NSF's NOIRLab in the USA, looked at the distribution of different ionised elements in the galaxy. The image on the right shows oxygen, nitrogen and hydrogen in blue, green and red respectively. The red glowing areas are regions of high star formation activity, whereas the dominant blue regions show the cone-shaped material flowing out of the AGN. The image on the left, which covers the same area, shows a more classical view of this galaxy, with dust lanes obscuring blue and orange starlight.

MUSE also allowed the team to map the motion of the stars and gas. They discovered that NGC 7582 may have a structure surrounding its central supermassive black hole that shields the rest of the galaxy from the harsh outflow of energy coming from the AGN, diverting it away from it in the form of an extremely powerful wind.

Alternative versions of this image

• Interactive comparison
• Video alternating between both images
• Individual image showing the star-formation and AGN activity
• Individual stellar image

Source:ESO/potw

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Saturn’s High-altitude Winds Generate Extraordinary Aurorae, Study Finds

Infrared image of saturn showing an aurora at its southern pole, captured by the cassini spacecraft.
Credit: NASA, Cassini, VIMS Team, University of Arizona, University of Leicester, JPL, ASI

Maunakea, Hawaiʻi Space scientists have discovered a never-before-seen mechanism fueling huge planetary aurorae at Saturn

A University of Leicester-led team has found that Saturn is unique among planets observed to date in that some of its aurorae are generated by swirling winds within its own atmosphere, and not just from the planet’s surrounding magnetosphere.

The study, which is based on observations made with the W. M. Keck Observatory on Maunakea, Hawaiʻi Island, is published inGeophysical Research Letters.

At all other observed planets, including Earth, aurorae are only formed by powerful currents that flow into the planet’s atmosphere from the surrounding magnetosphere. These are driven by either interaction with charged particles from the Sun (as at the Earth) or volcanic material erupted from a moon orbiting the planet (as at Jupiter and Saturn).

This discovery changes scientists’ understanding of planetary aurorae and answers one of the first mysteries raised by NASA’s Cassini probe, which reached Saturn in 2004: why can’t we easily measure the length of a day on the Ringed Planet?

When it first arrived at Saturn, Cassini tried to measure the bulk rotation rate of the planet, that determines the length of its day, by tracking radio emission ‘pulses’ from Saturn’s atmosphere. To the great surprise of those making the measurements, they found that the rate appeared to have changed over the two decades since the last spacecraft to have flown past the planet – Voyager 2, also operated by NASA – in 1981.

“Saturn’s internal rotation rate has to be constant, but for decades researchers have shown that numerous periodic properties related to the planet – the very measurements we’ve used at other planets to understand the internal rotation rate, such as the radio emission – tend to change with time,” says PhD researcher Nahid Chowdhury, a member of the Planetary Science Group within the University of Leicester’s School of Physics and Astronomy and lead author of the study. “What’s more, there are also independent periodic features seen in the northern and southern hemispheres which themselves vary over the course of a season on the planet.”

Animation showing the type of winds within Saturn’s upper atmosphere that are driving the ionosphere to move in the direction observed by a University of Leicester-led team of scientists using W. M. Keck Observatory. This set of two vortices rotate around in the pole of the planet, driving currents within the ionosphere, which then reach out into the surrounding magnetosphere, producing the bright aurora and magnetic field changes observed by Cassini. Credit: James O’Donoghue, JAXA/Tom Stallard, University of Leicester.

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“Our understanding of the physics of planetary interiors tells us the true rotation rate of the planet can’t change this quickly, so something unique and strange must be happening at Saturn. Several theories have been touted since the advent of the NASA Cassini mission trying to explain the mechanisms behind these observed periodicities,” adds Chowdhury. “This study represents the first detection of the fundamental driver, situated in the upper atmosphere of the planet, which goes on to generate both the observed planetary periodicities and aurorae. It’s absolutely thrilling to be able to provide an answer to one of the longest standing questions in our field. This is likely to initiate some rethinking about how local atmospheric weather effects on a planet impact the creation of aurorae, not just in our own solar system but farther afield too.”

Astronomers and planetary scientists based at the University of Leicester led the study alongside colleagues from NASA’s Jet Propulsion Laboratory (JPL), the Japan Aerospace Exploration Agency (JAXA), and the Universities of Wisconsin-Madison, Boston, and Lancaster, plus Imperial and University Colleges, London, to resolve the decades-old question.

They measured infrared emission from the gas giant’s upper atmosphere using Keck Observatory’s Near-Infrared Spectrograph (NIRSPEC) and mapped the varying flows of Saturn’s ionosphere, far below the magnetosphere, over the course of a month in 2017.

“This was one of the best observing experiences I’ve ever had,” says Tom Stallard, Associate Professor in Planetary Astronomy at the University of Leicester and co-author of the study. “It was a joy to be able to spend so much time at Keck, taking a couple of hours of data at the start of the night, once every four to five nights, during my five-week stay in Hawaiʻi. The opportunity to work with Keck’s team enabled us to capture one of the most exquisite datasets we’ve ever produced!”

The infrared emission map, when fixed against the known pulse of Saturn’s radio aurorae, showed that a significant proportion of the planet’s aurorae are generated by the swirling pattern of weather in its atmosphere and are responsible for the planet’s observed variable rate of rotation. Researchers believe the system is driven by energy from Saturn’s thermosphere, with winds in the ionosphere observed between 0.3 and 3.0 kilometers per second.

Simplified figure showing the direction of winds within layers of Saturn’s atmosphere.
Credit: Nahid Chowdhury/University of Leicester

“The University of Leicester has long been involved in measuring the effects of this new discovery – we’ve observed how the pulsing aurorae and the wobbling magnetic field lines stretching out into space highlight an apparently changing rotation rate. For two decades our researchers, along with the wider scientific community, have speculated about what might be driving these strange periodicities,” says Stallard. “Over the years, scientific meetings have had late-night discussions about whether the volcanic moon Enceladus might be the cause, or interactions with the thick atmosphere of the moon Titan, or perhaps interactions with Saturn’s bright rings. But recently, many researchers have focused on the possibility that it is Saturn’s upper atmosphere that causes this variability.”

“This search for a new type of aurora harks back to some of the earliest theories about Earth’s aurora,” adds Stallard. “We now know that aurorae on Earth are powered by interactions with the stream of charged particles driven from the Sun. But I love that the name Aurora Borealis originates from the ‘the Dawn of the Northern Wind.’ These observations have revealed that Saturn has a true Aurora Borealis – the first ever aurora driven by the winds in the atmosphere of a planet.”

“Our study, by conclusively determining the origin of the mysterious variability in radio pulses, eliminates much of the confusion into Saturn’s bulk rotation rate and the length of the day on Saturn,” says Kevin Baines, a JPL-Caltech-based co-author of the study and a member of the Cassini Science Team.

The variable rotation rates observed at Saturn have prevented scientists from using the regular pulse of radio emissions to calculate the bulk internal rotation rate. Fortunately, Cassini scientists developed a novel method using gravity-induced perturbations in Saturn’s complex ring system. This technique now seems to be the most accurate means of measuring the planet’s bulk rotational period, which was determined in 2019 to be 10 hours, 33 minutes, and 38 seconds.

This work was supported by a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute.

Source: W. M. Keck Observatory

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About NIRSPEC

The Near-Infrared Spectrograph (NIRSPEC) is a unique, cross-dispersed echelle spectrograph that captures spectra of objects over a large range of infrared wavelengths at high spectral resolution. Built at the UCLA Infrared Laboratory by a team led by Prof. Ian McLean, the instrument is used for radial velocity studies of cool stars, abundance measurements of stars and their environs, planetary science, and many other scientific programs. A second mode provides low spectral resolution but high sensitivity and is popular for studies of distant galaxies and very cool low-mass stars. NIRSPEC can also be used with Keck II’s adaptive optics (AO)system to combine the powers of the high spatial resolution of AO with the high spectral resolution of NIRSPEC. Support for this project was provided by the Heising-Simons Foundation.

About W. M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaiʻi feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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A Cosmic Draw

Arp 282
Credit: ESA/Hubble & NASA, J. Dalcanton, Dark Energy Survey, DOE, FNAL/DECam, CTIO/NOIRLab/NSF/AURA, SDSS
Acknowledgement: J. Schmidt

It is now widely accepted amongst astronomers that an important aspect of how galaxies evolve is the way they interact with one another. Galaxies can merge, collide, or brush past one another — each of which has a significant impact on their shapes and structures. As common as these interactions are thought to be in the Universe, it is rare to capture an image of two galaxies interacting in such a visibly dynamic way. This image, from the NASA/ESA Hubble Space Telescope, feels incredibly three-dimensional for a piece of deep-space imagery.

The subject of this image is named Arp 282, an interacting galaxy pair that is composed of the Seyfert galaxy NGC 169 (bottom) and the galaxy IC 1559 (top). If you’re interested in learning more about Seyfert galaxies, you can read about the Seyfert galaxy NGC 5728 here. Interestingly, both of the galaxies comprising Arp 282 have monumentally energetic cores, known as active galactic nuclei (AGN), although it is difficult to tell that from this image. This is actually rather fortunate, because if the full emission of two AGNs was visible in this image, then it would probably obscure the beautifully detailed tidal interactions occurring between NGC 169 and IC 1559. Tidal forces occur when an object’s gravity causes another object to distort or stretch. The direction of the tidal forces will be away from the lower-mass object and towards the higher mass object. When two galaxies interact, gas, dust and even entire solar systems will be drawn away from one galaxy towards the other by these tidal forces. This process can actually be seen in action in this image — delicate streams of matter have formed, visibly linking the two galaxies.

Source: ESA/Hubble/potw

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Gigapixel radio image of the Universe using Europe as a radio telescope

An illustration of the difference in resolving power between using only the Dutch LOFAR stations and all of the international stations throughout Europe, arranged in the formation of an HBA core stations. The animation fades from an angular resolution of 6" to a resolution of 0.3". Credit: Frits Sweijen

An international team of astronomers has created one of the largest and most detailed radio maps at megahertz frequencies thanks to Dutch supercomputers. This research, led by Frits Sweijen at Leiden University, has been published in Nature Astronomy on Thursday. Using the International LOFAR Telescope they have, in the wake of tremendous progress late last year, mapped an area of the sky the size of 25 full moons in great detail, with a resolving power comparable to optical telescopes on Earth. The resulting radio image contains nearly seven billion pixels and contains just shy of 2500 radio galaxies.

LOFAR

The sky is filled with radiation invisible to the naked eye, including radio waves at frequencies ten million times lower than red light. With tens of thousands of antennas across Europe, the LOFAR telescope listens to those cosmic radio waves at a frequency of 144 MHz, just above the FM radio band. Through these antennas the European continent transforms into an almost 2000 km big radio telescope. This tremendous size means that LOFAR can see exquisite and unprecedented detail at such low radio frequencies, with a resolving power high enough to make out the Great Pyramid if it were on the Moon. The combined area of all the antennas make it sensitive enough to detect a mobile phone ringing all the way out on Mars.

This resolving power is challenged by Earth's atmosphere however. Ultraviolet radiation from the Sun creates a layer of charged particles in the upper atmosphere. This so-called ``ionosphere'' distorts radio waves from space before they reach the telescope. For LOFAR it therefore is like looking at the sky from the bottom of the ocean. With advanced techniques these distortions can be corrected, focusing the telescope across its entire field of view, thus allowing it to be mapped.

Super computers

Determining these corrections and subsequently converting radio waves into an image, requires modern algorithms and a lot of compute power. Thanks to super computers this was not an issue. Locally, the Academic Leiden Interdisciplinary Cluster Environment (ALICE) lent its power to the scientists. Nationally, SURF in the Netherlands, provided early access to the new platform data processing platform named Spider. This platform is specifically designed for data-intensive projects like this. Lengthy calculations could be run in a massively parallel fashion thanks to these supercomputers. The final image was too large to be made in one go. To image the full field of view, it was processed in 25 smaller chunks each covering an area the size of a full moon. Each of these chunks was turned into an image over seven days, using software recently developed at ASTRON. Piece by piece, on a single computer, this process would have taken more than 175 days to complete. Thanks to the large scale compute infrastructure at Leiden and SURF, however, it only took seven days effectively.

The sharp eyes of the International LOFAR Telescope allow scientists to study the evolution of black holes and their host galaxies in more detail than before. Galaxies in the early Universe, for example, that would otherwise be too small to resolve due to their distance or young age, can have their spatial structure studied. The published results enable this for thousands of sources at once. With its near seven billion pixels this single image contains almost as many pixels as radio surveys from the past did covering the entire sky. These new results explore a tip of the ice berg with a detailed map of the entire Northern sky as the future goal.

This work made use of the Dutch national e-infrastructure with the support of the SURF Cooperative using grant no. EINF-251; the ERC Starting Grant ClusterWeb 804208; the Medical Research Council grant MR/T042842/1; the UK STFC ST/R000972/1 and ST/V000594/1 grants and the Academic Leiden Interdisciplinary Cluster Environment (ALICE) provided by Leiden University.

Article in Nature

Source:ASTRON-Netherlands Institute for Radio Astronomy/News

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Hubble Revisits a Galactic Oddball

NGC 1705
Text credit: European Space Agency (ESA
Image credit: ESA/Hubble & NASA, R. Chandar

The dwarf galaxy NGC 1705 featured in this image from the NASA/ESA Hubble Space Telescope lies in the southern constellation Pictor, approximately 17 million light-years from Earth. NGC 1705 is a cosmic oddball – it is small, irregularly shaped, and has recently undergone a spate of star formation known as a starburst.

Despite these eccentricities, NGC 1705 and other dwarf irregular galaxies like it can provide valuable insights into the overall evolution of galaxies. Dwarf irregular galaxies tend to contain few elements other than hydrogen or helium and are thought to be similar to the earliest galaxies that populated the universe.

The data shown in this image come from a series of observations designed to unveil the interplay between stars, star clusters, and ionized gas in nearby star-forming galaxies. By observing a specific wavelength of light known as H-alpha with Hubble’s Wide Field Camera 3, astronomers aimed to discover thousands of emission nebulae – regions created when hot, young stars bathe the clouds of gas surrounding them in ultraviolet light, causing them to glow.

This is not the first time that Hubble has imaged NGC 1705. Astronomers peered into the heart of the galaxy in 1999 using Hubble’s workhorse camera at the time, the Wide Field and Planetary Camera 2. This instrument was replaced with the Wide Field Camera 3 during the fifth and final Space Shuttle mission to Hubble in 2009, and the newer instrument has provided a richer and far more detailed portrait of NGC 1705 than the 1999 observation.

Media Contact:

Claire Andreoli
NASA's Goddard Space Flight Center
301-286-1940

Editor: Andrea Gianopoulos

Source: NASA/Hubble

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Puffy Planets lose atmospheres, become Super-Earths

This is an artist's Illustration of the mini-Neptune TOI 560.01, located 103 light-years away in the Hydra constellation. The planet, which orbits closely to its star, is losing its puffy atmosphere and may ultimately transform into a super-Earth. Credits: Artwork: Adam Makarenko (Keck Observatory)

Release images | Release Videos

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Exoplanets come in shapes and sizes that are not found in our solar system. These include small gaseous planets called mini-Neptunes and rocky planets several times Earth's mass called super-Earths.

Now, astronomers have identified two different cases of "mini-Neptune" planets that are losing their puffy atmospheres and likely transforming into super-Earths. Radiation from the planets' stars is stripping away their atmospheres, driving the hot gas to escape like steam from a pot of boiling water. The new findings help paint a picture of how exotic worlds like these form and evolve, and help explain a curious gap in the size distribution of planets found around other stars.

Mini-Neptunes are smaller, denser versions of the planet Neptune in our solar system, and are thought to consist of large rocky cores surrounded by thick blankets of gas. In the new studies, a team of astronomers used NASA's Hubble Space Telescope to look at two mini-Neptunes orbiting HD 63433, a star located 73 light-years away. And they used the W. M. Keck Observatory in Hawaii to study one of two  mini-Neptune planets in the star system called TOI 560, located 103 light-years away.

Their results show that atmospheric gas is escaping from the innermost mini-Neptune in TOI 560, called TOI 560.01 (also known as HD 73583b), and from the outermost mini-Neptune in HD 63433, called HD 63433c. This suggests that they could be turning into super-Earths.

"Most astronomers suspected that young, mini-Neptunes must have evaporating atmospheres," said Michael Zhang, lead author of both studies and a graduate student at Caltech. "But nobody had ever caught one in the process of doing so until now."

The study also found, surprisingly, that the gas around TOI 560.01 was escaping predominantly toward the star.

"This was unexpected, as most models predict that the gas should flow away from the star," said professor of planetary science Heather Knutson of Caltech, Zhang's advisor and a co-author of the study. "We still have a lot to learn about how these outflows work in practice."

New Clues to Missing Link in Planetary Types

Since the first exoplanets orbiting sun-like stars were discovered in the mid-1990s, thousands of other exoplanets have been found. Many of these orbit close to their stars, and the smaller, rocky ones generally fall into two groups: the mini-Neptunes and super-Earths. The super-Earths are as large as 1.6 times the size of Earth (and occasionally as large as 1.75 times the size of Earth), while the mini-Neptunes are between 2 and 4 times the size of Earth. Planets of these types are not found in our solar system. In fact, few planets with sizes between these two ranges have been detected around other stars.

One possible explanation for this size-gap is that the mini-Neptunes are transforming into the super-Earths. The mini-Neptunes are theorized to be cocooned by primordial atmospheres made of hydrogen and helium. The hydrogen and helium are left over from the formation of the central star, which is born out of clouds of gas. If a mini-Neptune is small enough and close enough to its star, stellar X-rays and ultraviolet radiation can strip away its primordial atmosphere over a period of hundreds of millions of years, scientists theorize. This would then leave behind a rocky super-Earth with a substantially smaller diameter (which could, in theory, still retain a relatively thin atmosphere similar to that surrounding our planet Earth).

"A planet in the size-gap would have enough atmosphere to puff up its radius, making it intercept more stellar radiation and thereby enabling fast mass loss," said Zhang. "But the atmosphere is thin enough that it gets lost quickly. This is why a planet wouldn't stay in the gap for long."

Other scenarios could explain the size-gap, according to the astronomers. For instance, the smaller rocky planets might have never gathered gas envelopes in the first place, and mini-Neptunes could be water worlds and not enveloped in hydrogen gas. This latest discovery of two mini-Neptunes with escaping atmospheres represents the first direct evidence to support the theory that mini-Neptunes are indeed turning into super-Earths.

Signatures in the Sunlight

The astronomers were able to detect the escaping atmospheres by watching the mini-Neptunes cross in front of, or transit, their host stars. The planets cannot be seen directly but when they pass in front of their stars as seen from our point of view on Earth, telescopes can look for absorption of starlight by atoms in the planets' atmospheres. In the case of the mini-Neptune TOI 560.01, the researchers found signatures of helium. For the star system HD 63433, the team found signatures of hydrogen in the outermost planet they studied, called HD 63433c, but not the inner planet, HD 63433b.

"The inner planet may have already lost its atmosphere," explained Zhang.

"The speed of the gases provides the evidence that the atmospheres are escaping. The observed helium around TOI 560.01 is moving as fast as 20 kilometers per second, while the hydrogen around HD 63433c is moving as fast as 50 kilometers per second. The gravity of these mini-Neptunes is not strong enough to hold on to such fast-moving gas. The extent of the outflows around the planets also indicates escaping atmospheres; the cocoon of gas around TOI 560.01 is at least 3.5 times as large as the radius of the planet, and the cocoon around HD 63433c is at least 12 times the radius of the planet."

The observations also revealed that the gas lost from TOI 560.01 was flowing toward the star. Future observations of other mini-Neptunes should reveal if TOI 560.01 is an anomaly or whether an inward-moving atmospheric outflow is more common.

"As exoplanet scientists, we've learned to expect the unexpected," Knutson said. "These exotic worlds are constantly surprising us with new physics that goes beyond what we observe in our solar system."

The findings are being published in two separate papers in The Astronomical Journal.

Credits:  Release: NASA, ESA, STScI, Caltech, Keck Observatory

Media Contact:

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland

Whitney Clavin
California Institute of Technology, Pasadena, California

Mari-Ela Chock
W. M. Keck Observatory, Mauna Kea, Hawaii

Science Contact:

Michael Zhang
California Institute of Technology, Pasadena, California

Heather A. Knutson
California Institute of Technology, Pasadena, California

Contact us:
Direct inquiries to the News Team

Related links and documents:

• The Hubble-based science paper by M. Zhang et al. (on arXiv)
• The Keck-based science paper by M. Zhang et al. (on arXiv)
• W. M. Keck Observatory's Release
• Caltech's Release
• NASA's Hubble Portal

Source: HubbleSite/News

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The Early Cooling of our Universe

Fig. 1: The Cosmic Microwave Background (left) was released 380,000 years after the Big Bang, and it acts as a background to all galaxies in the Universe. The starburst galaxy HFLS3 is embedded in a large cloud of cold water vapour (middle, indicated in blue), and is observed 880 million years after the Big Bang. Because of its low temperature, the water casts a dark shadow on the Microwave background (zoom-in panel on the left), corresponding to a contrast about 10,000 times stronger than its intrinsic fluctuations of only 0.001% (light/dark spots). © Telescope picture: IRAM/MPIA; galaxy illustration: ESA; microwave background image: ESA and the Planck collaboration; zoom-in panel: Dominik Riechers, Universität zu Köln; image composition: Martina Markus, Universität zu Köln.

Shadow of cosmic water cloud reveals the temperature of the young Universe

An international group of astrophysicists including Axel Weiß from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has developed a new method of measuring the cosmic microwave background temperature of the young Universe only 880 million years after the Big Bang. It is the first time that the temperature of the cosmic microwave background radiation – a relic of the energy released by the Big Bang – has been measured at such an early epoch of the Universe. The prevailing cosmological model assumes that the Universe has cooled off since the Big Bang – and still continues to do so. The model also describes how the cooling process should proceed, but so far it has been directly confirmed only for relatively recent cosmic epochs. The discovery not only sets a very early milestone in the development of the cosmic background temperature, but could also have implications for the enigmatic dark energy.

The result is published in this week’s issue of “Nature”.

The scientists used the NOEMA (Northern Extended Millimeter Array) observatory in the French Alps, the most powerful radio telescope in the Northern Hemisphere, to observe HFLS3, a galaxy showing a massive burst of star formation in a distance corresponding to an age of only 880 million years after the Big Bang. They discovered a screen of cold water gas that casts a shadow on the cosmic microwave background radiation. The shadow appears because the colder water absorbs the warmer microwave radiation on its path towards Earth, and its darkness reveals the temperature difference. As the temperature of the water can be determined from other observed properties of the starburst, the difference indicates the temperature of the Big Bang’s relic radiation, which at that time was about six times higher than in the Universe today.

“Other than proof for cooling, this discovery also shows us that the Universe in its infancy had some quite specific physical characteristics that no longer exist today”, says lead author Prof. Dominik Riechers from the University of Cologne’s Institute of Astrophysics. “Quite early, about 1.5 billion years after the Big Bang, the cosmic microwave background was already too cold for this effect to be observable. We have therefore a unique observing window that opens up to a very young Universe only”, he continues. In other words, if a galaxy with otherwise identical properties as HFLS3 were to exist today, the water shadow would not be observable because the required contrast in temperatures would no longer be available.

“This important milestone not only confirms the expected cooling trend for a much earlier epoch than has previously been possible, but could also have direct implications for the nature of the elusive dark energy”, says Dr Axel Weiß from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, the second author of the study. He further explains: “That is to say, an expanding Universe in which the density of dark energy does not change.” Dark energy is thought to be responsible for the accelerated expansion of the Universe over the past few billion years, but its properties remain poorly understood because it cannot be directly observed with the currently available facilities and instruments. However, its properties influence the evolution of cosmic expansion, and hence the cooling rate of the Universe over cosmic time. Based on this experiment, the properties of dark energy remain – for now - consistent with those of Einstein’s ’cosmological constant’.

Having discovered one such cold water cloud, the team is now setting out to find many more across the sky. Their aim is to map out the cooling of the Big Bang echo within the first 1.5 billion years of cosmic history. ‘This new technique provides important new insights into the evolution of the Universe, including the properties of dark energy, which are very difficult to constrain otherwise at such early epochs,’ Riechers said.

‘Our team is already following this up with NOEMA by studying the surroundings of other galaxies”, says co-author and NOEMA project scientist Dr Roberto Neri. “With the expected improvements in precision from studies of larger samples of water clouds, it remains to be seen if our current, basic understanding of dark energy holds.’

Fig. 2: Antennas of the NOEMA observatory in the French Alps (MPG/Germany, CNRS/France, IGN/Spain). Using their unique resolving power, astronomers probed the early Universe and found a new method for measuring the cosmic microwave background’s temperature. © IRAM, A. Rambaud

Background information:

NOEMA, the “NOrthern Extended Millimeter Array”, is the most powerful radio telescope in the Northern Hemisphere. The observatory operates at over 2500 meters above sea level on one of the most extended European high-altitude sites, the Plateau de Bure in the French Alps.

The telescope is operated by the Institut de Radioastronomie Millimétrique (IRAM) and is financed by the Max-Planck Society (Germany), the Centre National de Recherche Scientifique (France) and the Instituto Geografico Nacional (Spain).

Dominik Riechers (University of Cologne) conducted the study together with his colleagues Axel Weiß (Max Planck Institute for Radio Astronomy, MPIfR), Fabian Walter (Max Planck Institute for Astronomy, MPIA), Christopher L. Carilli (National Radio Astronomy Observatory, NRAO), Pierre Cox (Centre National de Recherche Scientifique, CNRS), Roberto Decarli (INAF -Osservatorio di Astrofisica e Scienza dello Spazio), and Roberto Neri (Institut de RadioAstronomie Millimétrique, IRAM).

The study has been funded by the US National Science Foundation (NSF), the Alexander von Humboldt Foundation (AvH), the Max-Planck-Society (MPG), Centre national de la recherche scientifique (CNRS), and Instituto Geográfico Nacional (IGN).

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Contact:

Dr. Axel Weiß
tel: +49 228 525-273
Max-Planck-Institut für Radioastronomie, Bonn

Prof. Dr. Dominik Riechers
tel: +49 221 470-76027
Astrophysik, I. Physik, Universität zu Köln

Dr. Norbert Junkes
Press and Public Outreach
tel: +49 228 525-399
Max Planck Institute for Radio Astronomy, Bonn

Original Paper:

Microwave Background Temperature at Redshift 6.34 from H2O Absorption

D. Riechers et al., 2022, Nature, 3. Februar 2022 (DOI: 10.1038/s41586-021-04294-5), after the embargo expires. Requests under embargo to press@nature.com

Source: Max Planck for Radio Astronomy/Press Releases

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New analysis leads to a fundamentally different view of supermassive black holes

Artist's impression of the quasar ULAS J1120+0641

Credit: ESO/M. Kornmesser

ASTROPHYSICS: In the center of most galaxies lies a supermassive black hole. Some of these are actively feeding on the gas and dust around them, expelling excess energy as powerful jets that are seen as quasars across the entire observable Universe. A new study led by astronomers at the Cosmic Dawn Center reviewed this process using new techniques — and the results may change how we think about the diets of these cosmic behemoths.

Located in the center of galaxies, supermassive black holes are millions or even billion times more massive than our Sun. With their extreme gravitational pull, they are able to engulf vast amounts of gas, dust, and perhaps even stars that wander into their vicinity.

Physics tells us that this material tends to form a disk as it is drawn towards the black hole in a phenomenon called “accretion”. Now these accretion disks are some of the most uninviting, violent places in the known Universe, with velocities approching the speed of light, and temperatures far in excess of the surface of our Sun. This heat produces radiation which we see as light, but the conversion of heat to light is so efficient — about 30 times more efficient than nuclear fusion — that physicists don’t quite understand how.

The supermassive black hole in the center of the galaxy M87. The streaks show the polarized light from the electric field of the gas plummeting into the black hole. Credit: EHT Collab. et al. 2021

Hungry cosmic behemoths

The dietary patterns of black holes have wide range. Some, like the one in our own Galaxy, aren’t very hungry and don’t seem to have accretion disks. But we see other galaxies with ravenous hunger whose supermassive black holes have grown extremely hot accretion disks so bright that they outshine all of the stars in their galaxy.

Only recently have we obtained our first picture of an accretion disk from the Event Horizon Telescope, a worldwide network of radio telescopes. However, this accretion disk belongs to a very nearby galaxy. We cannot repeat this experiment with more distant galaxies as the disks are simply too small and so are unresolved, even by the largest telescopes.

Variability is key

Fortunately another method of probing the size and structure of distant accretion disks seems promising: Although we cannot resolve the disks' various components, we can study how its intensity varies in time. By studying the variations in the disks' light we can piece together a picture of the accretion disks of even the most distant galaxies.

This is what DAWN PhD Fellow John Weaver has done, looking into past observations of more than 9,000 galaxies with bright accretion disks — the so-called quasars — from the observational program "Sloan Digital Sky Survey".

When the source is not resolved, the observed light from the accretion disk will be “contaminated” by light from the galaxy hosting the black hole. This unwanted light from the host galaxies has largely been ignored by previous studies. However, by using a new model for the variations in the quasar light, John Weaver and his collaborator Keith Horne, professor of astronomy at the University of St Andrews, were able to separate the light of the accretion disk from that of the host galaxy.

In other words, the model allowed them to more directly see the light from the accretion disk around supermassive black holes, even in galaxies billions of lightyears away.

Obscured by dust

What Weaver and Horne found was that cosmic dust near the accretion disk was likely blocking their view. Using several different models of cosmic dust to account for, and remove, its obscuring effects, they were able to determine how hot the accretion disk is, both near the black hole and far from it at the edges of the disk.

This difference in temperature between the hot inner disk and the cold outer disk has been theoretically predicted. However, what Weaver and Horne found observationally was a very different picture of the temperature of the disk: the disks turned out to be even hotter near the black hole than predicted. These unexpected findings were published today in the Monthly Notices of The Royal Astronomical Society and suggest that our assumptions and theoretical models need to be revised — with consequences for our understanding of supermassive black holes altogether.

Not only do we have more to learn about supermassive black holes, but the variations in their ravenous hunger are a marvelous demonstration that our Universe is a far more dynamic place than one would expect looking at the static night time sky.

Source: Niels Bohr Institute University of Copenhagen/News

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Even dying stars can still give birth to planets

Artistic impression
Credit: N. Stecki

Planets are usually not much older than the stars around which they revolve. Take the Sun: it was born 4.6 billion years ago, and not long after that, Earth came into the world. But KU Leuven astronomers have discovered that a completely different scenario is also possible. Even if they are near death, some types of stars can possibly still form planets. If this is confirmed, theories on planet formation will need to be adjusted.

Planets such as Earth, and all other planets in our solar system, were formed not long after the Sun. Our Sun started to burn 4.6 billion years ago, and in the next million years, the matter around it clumped into protoplanets. The birth of the planets in that protoplanetary disc, a gigantic pancake made of dust and gas, so to speak, with the Sun in the middle, explains why they all orbit in the same plane.

But such discs of dust and gas needn’t necessarily only surround newborn stars. They can also develop independently from star formation, for example around binary stars of which one is dying (binary stars are two stars that orbit each other, also called a binary system). When the end approaches for a medium-sized star (like the Sun), it catapults the outer part of its atmosphere into space, after which it slowly dies out as a so-called white dwarf. However, in the case of binary stars, the gravitational pull of the second star causes the matter ejected by the dying star to form a flat, rotating disc. Moreover, this disc strongly resembles the protoplanetary discs that astronomers observe around young stars elsewhere in the Milky Way.

This we already knew. However, what is new is that the discs surrounding so-called evolved binary stars not uncommonly show signs that could point to planet formation, as discovered by an international team of astronomers led by KU Leuven researchers. What’s more, their observations show that this is the case for one in ten of these binary stars. “In ten per cent of the evolved binary stars with discs we studied, we see a large cavity (a void/opening, ed.) in the disc”, says KU Leuven astronomer Jacques Kluska, first author of the article in the journal Astronomy & Astrophysics in which the discovery is described. “This is an indication that something is floating around there that has collected all matter in the area of the cavity.”

Second-generation planets

The clean-up of the matter could be the work of a planet. That planet might not have formed at the very beginning of one of the binary stars’ life, but at the very end. The astronomers moreover found further strong indications for the presence of such planets. “In the evolved binary stars with a large cavity in the disc, we saw that heavy elements such as iron were very scarce on the surface of the dying star”, says Kluska. “This observation leads one to suspect that dust particles rich in these elements were trapped by a planet.” By the way, the Leuven astronomer doesn’t rule out the possibility that in this way, several planets can be formed around these binary stars.

The discovery was made when the astronomers were drawing up an inventory of evolved binary stars in our Milky Way. They did that based on existing, publicly available observations. Kluska and his colleagues counted 85 of such binary star pairs. In ten pairs, the researchers came across a disc with a large cavity on the infrared images.

Current theories put to the test

If new observations confirm the existence of planets around evolved binary stars, and if it turns out the planets were only formed after one of the stars had reached the end of its life, the theories on planet formation will need to be adjusted. “The confirmation or refutation of this extraordinary way of planet formation will be an unprecedented test for the current theories”, according to Professor Hans Van Winckel, head of the KU Leuven Institute of Astronomy.

The KU Leuven astronomers soon want to verify their hypothesis themselves. To this end, they will use the big telescopes of the European Southern Observatory in Chile to take a closer look at the ten pairs of binary stars whose discs show a large cavity.

More information

The study “A population of transition disks around evolved stars: fingerprints of planets” by J. Kluska et al. is published in Astronomy & Astrophysics.

translated by Miriel Vandeperre

Source: Ku Leuven/News

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