Hidden supermassive black holes brought to life by galaxies on collision course

Peer-Reviewed Publication

ROYAL ASTRONOMICAL SOCIETY

 

IMAGE: AN ARTIST’S IMPRESSION OF A DUSTY REGION AROUND A BLACK HOLE. THE MOST DUST-ENSHROUDED BLACK HOLES CAN COMPLETELY STOP X-RAYS AND VISIBLE LIGHT ESCAPING, BUT THE SAME DUST CAN BE HEATED BY A GROWING BLACK HOLE AND WILL GLOW BRIGHTLY AT INFRARED WAVELENGTHS. view more 

CREDIT: ESA/NASA, THE AVO PROJECT AND PAOLO PADOVANI

Astronomers have found that supermassive black holes obscured by dust are more likely to grow and release tremendous amounts of energy when they are inside galaxies that are expected to collide with a neighbouring galaxy. The new work, led by researchers from Newcastle University, is published in Monthly Notices of the Royal Astronomical Society.

Galaxies, including our own Milky Way, contain supermassive black holes at their centres. They have masses equivalent to millions, or even billions, times that of our Sun. These black holes grow by ‘eating’ gas that falls on to them. However, what drives the gas close enough to the black holes for this to happen is an ongoing mystery.

One possibility is that when galaxies are close enough together, they are likely to be gravitationally pulled towards each other and ‘merge’ into one larger galaxy.

In the final stages of its journey into a black hole, gas lights up and produces a huge amount of energy. This energy is typically detected using visible light or X-rays. However, the astronomers conducting this study were only able to detect the growing black holes using infrared light. The team made use of data from many different telescopes, including the Hubble Space Telescope and infrared Spitzer Space Telescope.

The researchers developed a new technique to determine how likely it is that two galaxies are very close together and are expected to collide in the future. They applied this new method to hundreds of thousands of galaxies in the distant universe (looking at galaxies formed 2 to 6 billion years after the Big Bang) in an attempt to better understand the so-called ‘cosmic noon’, a time when most of the Universe’s galaxy and black hole growth is expected to have taken place.

Understanding how black holes grew during this time is fundamental in modern day galactic research, especially as it may give us an insight into the supermassive black hole situated inside the Milky Way, and how our galaxy evolved over time.

As they are so far away, only a small number of cosmic noon galaxies meet the required criteria to get precise measurements of their distances. This makes it very difficult to know with high precision if any two galaxies are very close to each other.

This study presents a new statistical method to overcome the previous limitations of measuring accurate distances of galaxies and supermassive black holes at cosmic noon. It applies a statistical approach to determine galaxy distances using images at different wavelengths and removes the need for spectroscopic distance measurements for individual galaxies.

Data arriving from the James Webb Space Telescope over the coming years is expected to revolutionise studies in the infrared and reveal even more secrets about how these dusty black holes grow.

Sean Dougherty, postgraduate student at Newcastle University and lead author of the paper, says, “Our novel approach looks at hundreds of thousands of distant galaxies with a statistical approach and asks how likely any two galaxies are to be close together and so likely to be on a collision course.”

Dr Chris Harrison, co-author of the study, “These supermassive black holes are very challenging to find because the X-ray light, which astronomers have typically used to find these growing black holes, is blocked, and not detected by our telescopes. But these same black holes can be found using infrared light, which is produced by the hot dust surrounding them.”

He adds, “The difficulty in finding these black holes and in establishing precise distance measurements explains why this result has previously been challenging to pin down these distant ‘cosmic noon’ galaxies. With JWST we are expecting to find many more of these hidden growing black holes. JWST will be far better at finding them, therefore we will have many more to study, including ones that are the most difficult to find. From there, we can do more to understand the dust that surrounds them, and find out how many are hidden in distant galaxies.”

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JOURNAL

Monthly Notices of the Royal Astronomical Society

ESO telescope reveals hidden views of vast stellar nurseries

Peer-Reviewed Publication

ESO

 

IMAGE: THIS IMAGE SHOWS THE L1688 REGION IN THE OPHIUCHUS CONSTELLATION. NEW STARS ARE BORN IN THE COLOURFUL CLOUDS OF GAS AND DUST SEEN HERE. THE INFRARED OBSERVATIONS UNDERLYING THIS IMAGE REVEAL NEW DETAILS IN THE STAR-FORMING REGIONS THAT ARE USUALLY OBSCURED BY THE CLOUDS OF DUST. THE IMAGE WAS PRODUCED WITH DATA COLLECTED BY THE VIRCAM INSTRUMENT, WHICH IS ATTACHED TO THE VISTA TELESCOPE AT ESO’S PARANAL OBSERVATORY IN CHILE. THE OBSERVATIONS WERE DONE AS PART OF THE VISIONS SURVEY, WHICH WILL ALLOW ASTRONOMERS TO BETTER UNDERSTAND HOW STARS FORM IN THESE DUST-ENSHROUDED REGIONS. view more 

CREDIT: ESO/MEINGAST ET AL.

Using ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA), astronomers have created a vast infrared atlas of five nearby stellar nurseries by piecing together more than one million images. These large mosaics reveal young stars in the making, embedded in thick clouds of dust. Thanks to these observations, astronomers have a unique tool with which to decipher the complex puzzle of stellar birth.

“In these images we can detect even the faintest sources of light, like stars far less massive than the Sun, revealing objects that no one has ever seen before,” says Stefan Meingast, an astronomer at the University of Vienna in Austria and lead author of the new study published today in Astronomy & Astrophysics. “This will allow us to understand the processes that transform gas and dust into stars.”

Stars form when clouds of gas and dust collapse under their own gravity, but the details of how this happens are not fully understood. How many stars are born out of a cloud? How massive are they? How many stars will also have planets?

To answer these questions, Meingast’s team surveyed five nearby star-forming regions with the VISTA telescope at ESO’s Paranal Observatory in Chile. Using VISTA’s infrared camera VIRCAM, the team captured light coming from deep inside the clouds of dust. “The dust obscures these young stars from our view, making them virtually invisible to our eyes. Only at infrared wavelengths can we look deep into these clouds, studying the stars in the making,” explains Alena Rottensteiner, a PhD student also at the University of Vienna and co-author of the study.

The survey, called VISIONS, observed star-forming regions in the constellations of Orion, Ophiuchus, Chamaeleon, Corona Australis and Lupus. These regions are less than 1500 light-years away and so large that they span a huge area in the sky. The diameter of VIRCAM’s field of view is as wide as three full Moons, which makes it uniquely suited to map these immensely big regions.

The team obtained more than one million images over a period of five years. The individual images were then pieced together into the large mosaics released here, revealing vast cosmic landscapes. These detailed panoramas feature dark patches of dust, glowing clouds, newly-born stars and the distant background stars of the Milky Way.

Since the same areas were observed repeatedly, the VISIONS data will also allow astronomers to study how young stars move. “With VISIONS we monitor these baby stars over several years, allowing us to measure their motion and learn how they leave their parent clouds,” explains João Alves, an astronomer at the University of Vienna and Principal Investigator of VISIONS. This is not an easy feat, as the apparent shift of these stars as seen from Earth is as small as the width of a human hair seen from 10 kilometres away. These measurements of stellar motions complement those obtained by the European Space Agency’s Gaia mission at visible wavelengths, where young stars are hidden by thick veils of dust.

The VISIONS atlas will keep astronomers busy for years to come. “There is tremendous long-lasting value for the astronomical community here, which is why ESO steers Public Surveys like VISIONS,” says Monika Petr-Gotzens, an astronomer at ESO in Garching, Germany, and co-author of this study. Moreover, VISIONS will set the groundwork for future observations with other telescopes such as ESO’s Extremely Large Telescope (ELT), currently under construction in Chile and set to start operating later this decade. “The ELT will allow us to zoom into specific regions with unprecedented detail, giving us a never-seen-before close-up view of individual stars that are currently forming there,” concludes Meingast.

More information

This research was presented in the paper “VISIONS: The VISTA Star Formation Atlas”, to appear in Astronomy & Astrophysics (doi: 10.1051/0004-6361/202245771)

The team is composed of Stefan Meingast (University of Vienna, Austria [Vienna]), João Alves (Vienna), Hervé Bouy (Université de Bordeaux, France [Bordeaux]), Monika G. Petr-Gotzens (European Southern Observatory, Germany [ESO]), Verena Fürnkranz (Max-Planck-Institut für Astronomie, Germany [MPIA]]), Josefa E. Großschedl (Vienna), David Hernandez (Vienna), Alena Rottensteiner (Vienna), Joana Ascenso (Universidade do Porto, Portugal [Porto]; Universidade de Lisboa, Portugal [Lisboa]), Amelia Bayo (ESO; Universidad de Valparaíso, Chile), Erik Brändli (Vienna), Anthony G. A. Brown (Leiden University, Netherlands), Jan Forbrich (University of Hertfordshire, UK [Hertfordshire]), Alyssa Goodman (Harvard-Smithsonian Center for Astrophysics, USA [CfA]), Alvaro Hacar (Vienna), Birgit Hasenberger (Vienna), Rainer Köhler (The CHARA Array of Georgia State University, USA), Karolina Kubiak (Lisboa), Michael Kuhn (Hertfordshire), Charles Lada (CfA), Kieran Leschinski (Vienna), Marco Lombardi (Università degli Studi di Milano, Italy), Diego Mardones (Universidad de Chile, Chile), Núria Miret-Roig (European Space Agency, European Space Research and Technology Centre, Netherlands [ESA]), André Moitinho (Lisboa), Koraljka Mužiiić (Porto; Lisboa), Martin Piecka (Vienna), Laura Posch (Vienna), Timo Prusti (ESA), Karla Peña Ramírez (Universidad de Antofagasta, Chile), Ronny Ramlau (Johannes Kepler University Linz, Austria; Johann Radon Institute for Computational and Applied Mathematics, Austria), Sebastian Ratzenböck (Vienna; Research Network Data Science at Uni Vienna), Germano Sacco (INAF – Osservatorio Astrofisico di Arcetri, Italy), Cameren Swiggum (Vienna), Paula Stella Teixeira (University of St Andrews, UK), Vanessa Urban (Vienna), Eleonora Zari (MPIA), and Catherine Zucker (Bordeaux).

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 survey telescopes such as VISTA. 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 ALMA on Chajnantor, a facility that observes 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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DOI

10.1051/0004-6361/202245771 

Astronomers reveal the largest cosmic explosion ever seen

Peer-Reviewed Publication

UNIVERSITY OF SOUTHAMPTON

 

IMAGE: ARTIST IMPRESSION OF A BLACK HOLE ACCRETION view more 

CREDIT: CREDIT JOHN A. PAICE WWW.JOHNAPAICE.COM/

A team of astronomers led by the University of Southampton have uncovered the largest cosmic explosion ever witnessed.

The explosion is more than ten times brighter than any known supernova (exploding star) and three times brighter than the brightest tidal disruption event, where a star falls into a supermassive black hole.

The explosion, known as AT2021lwx, has currently lasted over three years, compared to most supernovae which are only visibly bright for a few months. It took place nearly 8 billion light years away, when the universe was around 6 billion years old, and is still being detected by a network of telescopes.

The researchers believe that the explosion is a result of a vast cloud of gas, possibly thousands of times larger than our sun, that has been violently disrupted by a supermassive black hole. Fragments of the cloud would be swallowed up, sending shockwaves through its remnants, as well as into a large dusty ‘doughnut’ surrounding the black hole. Such events are very rare and nothing on this scale has been witnessed before.

Last year, astronomers witnessed the brightest explosion on record - a gamma-ray burst known as GRB 221009A. While this was brighter than AT2021lwx, it lasted for just a fraction of the time, meaning the overall energy released by the AT2021lwx explosion is far greater.

The findings of the research have been published today [Friday, 12 May 2023] in Monthly Notices of the Royal Astronomical Society.

Discovery

AT2021lwx was first detected in 2020 by the Zwicky Transient Facility in California, and subsequently picked up by the Asteroid Terrestrial-impact Last Alert System (ATLAS) based in Hawaii. These facilities survey the night sky to detect transient objects that rapidly change in brightness indicating cosmic events such as supernovae, as well as finding asteroids and comets. Until now the scale of the explosion has been unknown.

“We came upon this by chance, as it was flagged by our search algorithm when we were searching for a type of supernova,” says Dr Philip Wiseman, Research Fellow at the University of Southampton, who led the research. “Most supernovae and tidal disruption events only last for a couple of months before fading away. For something to be bright for two plus years was immediately very unusual.”

The team investigated the object further with several different telescopes: the Neil Gehrels Swift Telescope (a collaboration between NASA, the UK and Italy), the New Technology Telescope (operated by the European Southern Observatory) in Chile, and the Gran Telescopio Canarias in La Palma, Spain.

Measuring the explosion

By analysing the spectrum of the light, splitting it up into different wavelengths and measuring the different absorption and emission features of the spectrum, the team were able to measure the distance to the object.

“Once you know the distance to the object and how bright it appears to us, you can calculate the brightness of the object at its source. Once we’d performed those calculations, we realised this is extremely bright,” says Professor Sebastian Hönig from the University of Southampton, a co-author of the research.

The only things in the universe that are as bright as AT2021lwx are quasars - supermassive black holes with a constant flow of gas falling onto them at high velocity.

Professor Mark Sullivan, also of the University of Southampton and another co-author of the paper, explains: “With a quasar, we see the brightness flickering up and down over time. But looking back over a decade there was no detection of AT2021lwx, then suddenly it appears with the brightness of the brightest things in the universe, which is unprecedented.”

What caused the explosion?

There are different theories as to what could have caused such an explosion, but the Southampton-led team believe the most feasible explanation is an extremely large cloud of gas (mostly hydrogen) or dust that has come off course from its orbit around the black hole and been sent flying in.

The team are now setting out to collect more data on the explosion - measuring different wavelengths, including X-rays which could reveal the object’s surface and temperature, and what underlying processes are taking place. They will also carry out upgraded computational simulations to test if these match their theory of what caused the explosion.

Dr Philip Wiseman added: “With new facilities, like the Vera Rubin Observatory’s Legacy Survey of Space and Time, coming online in the next few years, we are hoping to discover more events like this and learn more about them. It could be that these events, although extremely rare, are so energetic that they are key processes to how the centres of galaxies change over time.”

Multiwavelength observations of the extraordinary accretion event AT2021lwx is published in Monthly Notices of the Royal Astronomical Society and is available to read online.

Ends

Notes for editors

1. Multiwavelength observations of the extraordinary accretion event AT2021lwx will be published in Monthly Notices of the Royal Astronomical Society at 00:01 GMT on Friday 12 May 2023.
2. A preprint of the paper is available to read at: https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stad1000/7115325
3. For further information and interviews with the following, please contact: Steve Williams, Media Relations, University of Southampton. press@soton.ac.uk 023 8059 3212:
   • Dr Philip Wiseman, University of Southampton
   • Professor Sebastian Hönig, University of Southampton
   • Professor Mark Sullivan, University of Southampton
   • Associate Professor Manda Banerji, University of Southampton
   • Associate Professor Matthew Middleton, University of Southampton
4. Images
   1. Artist impression of a black hole accretion. Credit John A. Paice.
   2. Images of the Zwicky Transient Facility. Credit Caltech
   3. Images of the New Technology Telescope. Credit European Southern Observatory
5. The University of Southampton drives original thinking, turns knowledge into action and impact, and creates solutions to the world’s challenges. We are among the top 100 institutions globally (QS World University Rankings 2023). Our academics are leaders in their fields, forging links with high-profile international businesses and organisations, and inspiring a 22,000-strong community of exceptional students, from over 135 countries worldwide. Through our high-quality education, the University helps students on a journey of discovery to realise their potential and join our global network of over 200,000 alumni. www.southampton.ac.uk
6. The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognises outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

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JOURNAL

Monthly Notices of the Royal Astronomical Society

DOI

10.1093/mnras/stad1000 

ARTICLE TITLE

Multiwavelength observations of the extraordinary accretion event AT2021lwx

ARTICLE PUBLICATION DATE

12-May-2023

Portugal participates in the development of a first-class instrument for the largest telescope in the world

Reports and Proceedings

FACULTY OF SCIENCES OF THE UNIVERSITY OF LISBON

 

IMAGE: THIS ARTIST’S RENDERING SHOWS THE EXTREMELY LARGE TELESCOPE IN OPERATION ON CERRO ARMAZONES IN NORTHERN CHILE. THE TELESCOPE IS SHOWN USING LASERS TO CREATE ARTIFICIAL STARS HIGH IN THE ATMOSPHERE. THE FIRST STONE CEREMONY FOR THE TELESCOPE WAS ATTENDED BY THE PRESIDENT OF CHILE, MICHELLE BACHELET JERIA, ON 26 MAY 2017. view more 

CREDIT: ESO/L. CALÇADA

A research team from the University of Lisbon and University of Oporto (Portugal) participate in the development of METIS (Mid-infrared ELT Imager and Spectrograph). This powerful instrument will equip the largest telescope in the world - the Extremely Large Telescope (ELT) - under construction by the European Southern Observatory (ESO) in Armazones, Chile.

At this critical acceptance stage of the complete and final METIS design, ESO is presenting an illustrative film demonstrating the exceptional capabilities of the instrument. The presentation will take place on May 12, at 4:00pm (CEST).

METIS will detect radiation that is invisible to the human eye, that is, radiation that is “felt” in the form of “heat”. The instrument will take advantage of the ELT's giant primary mirror, measuring around 39 meters, to study a myriad of scientific topics, from objects in our solar system to distant active galaxies with revolutionary precision.

“This is one of the ELT's most complex instruments and the participation of the Portuguese team is proof of national capabilities in the development of large international projects. Involvement in this project not only allows them to apply their experience, but also to increase it, given the inherent challenges. It also allows Portugal to be at the forefront at the time of observations, and, in addition, promotes the participation of industry, involving the ecosystem as a whole”, says Marta Gonçalves, manager of Science and Education projects at the Portuguese Space Agency.

“Participating in the development of METIS has been a huge challenge, which has put our capacities for innovation, simulation, and construction of instruments for Astrophysics to the test. Projects like this also help to develop and promote the participation of Portuguese industry in major international projects. They strategically position us at the forefront as teachers, researchers, engineers and students”, says António Amorim, responsible for the Portuguese participation in METIS, Professor in the Physics Department of the Faculty of Sciences of the University of Lisbon (Ciências ULisboa) and member of CENTRA – Center for Astrophysics and Gravitation.

The Portuguese participation in the development of METIS has several fronts. The main contribution is the construction of the mechanical support structure, alignment and access to the instrument called Warm Support Structure (WSS). Portugal also contributes to the METIS operations team and also to the scientific team.

The total cost of the METIS instrument is around €95 million, and its mass is around 12 tons (equivalent to a double-decker bus). For Mercedes Filho, manager of METIS project in Portugal and researcher at the Physical Engineering Department at the Faculty of Engineering of University of Oporto (FEUP), “the WSS has extreme requirements. On the one hand, the WSS must position the instrument with an accuracy of 10 millionths of a rotation and 100 millionths of a meter. On the other hand, the WSS must withstand a major earthquake in complete safety, being able to support an equivalent mass of 40 tons!”.

The METIS project also involved the participation of PhD and Master's students, namely André Bone and Ricardo Costa, the former a PhD student in Physical Engineering at Ciências ULisboa and the latter a Master’s student in Mechanical Engineering at FEUP.

As for Astrophysics, many scientific discoveries are being prepared in detail given the extremely high cost and competition for infrastructure, as explained by Paulo Garcia, co-responsible for the Portuguese participation in METIS, researcher at CENTRA, and professor at the Department of Physical Engineering (DEF) at FEUP: “Portugal will have privileged access to METIS, to carry out observations of celestial phenomena with a top scientific instrument that transports us to the future of astrophysics. METIS will allow an unprecedented study of several astrophysical topics, and our priority at CENTRA is to study gravity in the vicinity of the supermassive black hole at the center of our galaxy. In particular, we intend to detect new stars in orbits closer to the black hole than currently known and study their motion.”

Other Portuguese researchers involved in the scientific preparation of this initiative are André Moitinho, Professor at Ciências Ulisboa, Koraljka Muzic, researcher at FEUP, and Alexandre Correia, professor at the Physics Department at the University of Coimbra.

The ELT is under construction in Armazones, Chile by ESO. The ELT will be the largest terrestrial optical and infrared telescope when it begins operations, scheduled for the middle of this decade. With its 39-meter diameter primary mirror and advanced adaptive optics systems, the telescope will be able to see details six times finer than the James Webb Space Telescope and 20 times finer than the Hubble Telescope.

  

METIS will be one of the detection instruments placed on the ELT platform.

CREDIT

ESO/METIS Consortium / L. Calçada

METIS International Consortium

The METIS consortium is made up of NOVA (Netherlands Research School for Astronomy, represented by Leiden University, The Netherlands), UK Astronomy Technology Center (UKATC, and Edinburgh, Scotland, UK), Max Planck Institute for Astronomy (MPIA, based in Heidelberg, Germany), Katholieke Universiteie Leuven (Belgium), Saclay Nuclear Research Center (CEA Saclay, France), ETH Zürich (Switzerland), A* (an Austrian partnership represented by the University of Vienna, the University of Innsbruck, the University of Graz , University of Linz, and RICAM Linz, Austrian Academy of Sciences, Austria), Universitat zu Koln (Germany), Ciências Ulisboa and FEUP, represented by CENTRA (Portugal), University of Liège (Belgium), Academia Sinica Institute of Astronomy and Astrophysics in Taipei (Taiwan) and the University of Michigan at Ann Arbor (USA), and, with contributions from ESO.

 

Schedule (CEST)

4:00pm ELT trailer starts: https://cdn.eso.org/videos/hd_1080p25_screen/elt-teaser-2021.mp4
4:01pm Welcome given by Suzanna Randal
4:05pm Short talk about the ELT by Michele Cirasuolo
4:10pm Suzanna Randal introduces METIS
4:11pm The METIS movie
4:21pm Q&A Session

 

Links
YouTube: https://www.youtube.com/watch?v=zgHFdokFyLU
Facebook messages and event: https://www.facebook.com/ESOAstronomy/posts/pfbid0kahjP5PJVNa3fTrzuanVJscYBANRE4LUbGRdWaG7smSFbBpyqtSLJheXJP7jyD23l 
Twitter: https://twitter.com/ESO/status/1653422689690832902
Linkedin: https://www.linkedin.com/feed/update/urn:li:activity:7059189856576380928

New study puts a definitive age on Saturn’s rings—they’re really young

Peer-Reviewed Publication

UNIVERSITY OF COLORADO AT BOULDER

A new study led by physicist Sascha Kempf at the University of Colorado Boulder has delivered the strongest evidence yet that Saturn’s rings are remarkably young—potentially answering a question that has boggled scientists for well over a century. 

The research, to be published May 12 in the journal Science Advances, pegs the age of Saturn’s rings at no more than 400 million years old. That makes the rings much younger than Saturn itself, which is about 4.5 billion years old.

“In a way, we’ve gotten closure on a question that started with James Clerk Maxwell,” said Kempf, associate professor in the Laboratory for Atmospheric and Space Physics (LASP) at CU Boulder.

The researchers arrived at that closure by studying what might seem like an unusual subject: dust. 

Kempf explained that tiny grains of rocky material wash through Earth’s solar system on an almost constant basis. In some cases, this flux can leave behind a thin layer of dust on planetary bodies, including on the ice that makes up Saturn’s rings.

In the new study, he and his colleagues set out to put a date on Saturn’s rings by studying how rapidly this layer of dust builds up—a bit like telling how old a house is by running your finger along its surfaces.

“Think about the rings like the carpet in your house,” Kempf said. “If you have a clean carpet laid out, you just have to wait. Dust will settle on your carpet. The same is true for the rings.”

It was an arduous process: From 2004 to 2017, the team used an instrument called the Cosmic Dust Analyzer aboard NASA’s late Cassini spacecraft to analyze specks of dust flying around Saturn. Over those 13 years, the researchers collected just 163 grains that had originated from beyond the planet’s close neighborhood. But it was enough. Based on their calculations, Saturn’s rings have likely been gathering dust for only a few hundred million years.

The planet’s rings, in other words, are new phenomena, arising (and potentially even disappearing) in what amounts to a blink of an eye in cosmic terms. 

“We know approximately how old the rings are, but it doesn’t solve any of our other problems,” Kempf said. “We still don’t know how these rings formed in the first place.”

From Galileo to Cassini

Researchers have been captivated by these seemingly-translucent rings for more than 400 years. In 1610, Italian astronomer Galileo Galilei first observed the features through a telescope, although he didn’t know what they were. (Galileo’s original drawings make the rings look a bit like the handles on a water jug). In the 1800s, Maxwell, a scientist from Scotland, concluded that Saturn’s rings couldn’t be solid but were, instead, made up of many individual pieces. 

Today, scientists know that Saturn hosts seven rings comprised of countless chunks of ice, most no bigger than a boulder on Earth. Altogether, this ice weighs about half as much as Saturn’s moon Mimas and stretches nearly 175,000 miles from the planet’s surface. 

Kempf added that for most of the 20th Century, scientists assumed that the rings likely formed at the same time as Saturn. 

But that idea raised a few issues—namely, Saturn’s rings are sparkling clean. Observations suggest that these features are made up of roughly 98% pure water ice by volume, with only a tiny amount of rocky matter. 

“It’s almost impossible to end up with something so clean,” Kempf said.

Cassini offered an opportunity to put a definitive age on Saturn’s rings. The spacecraft first arrived at Saturn in 2004 and collected data until it purposefully crashed into the planet's atmosphere in 2017. The Cosmic Dust Analyzer, which was shaped a bit like a bucket, scooped up small particles as they whizzed by. 

Engineers and scientists at LASP designed and built a much more sophisticated dust analyzer for NASA’s upcoming Europa Clipper mission, which is scheduled to launch in 2024.

The team estimated that this interplanetary grime would contribute far less than a gram of dust to each square foot of Saturn’s rings every year—a light sprinkle, but enough to add up over time. Previous studies had also suggested that the rings could be young but didn’t include definitive measures of dust accumulation.

Stroke of luck

The rings might already be vanishing. In a previous study, NASA scientists reported that the ice is slowly raining down onto the planet and could disappear entirely in another 100 million years.

That these ephemeral features existed at a time when Galileo and the Cassini spacecraft could observe them seems almost too good to be true, Kempf said—and it begs an explanation for how the rings formed in the first place. Some scientists, for example, have posited that Saturn’s rings may have formed when the planet’s gravity tore apart one of its moons.

 “If the rings are short lived and dynamical, why are we seeing them now?” he said. “It’s too much luck.”

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Co-authors on the new study include Nicolas Altobelli of the European Space Agency; Jürgen Schmidt of the Freie Universität Berlin; Jeffrey Cuzzi and Paul Estrada of the NASA Ames Research Center; and Ralf Srama of the Universität Stuttgart.

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JOURNAL

Science Advances

DOI

10.1126/sciadv.adf8537 

ARTICLE TITLE

Micrometeoroid infall onto Saturn’s rings constrains their age to no more than a few hundred million years

ARTICLE PUBLICATION DATE

12-May-2023

Disclaimer: AAAS an

Celestial monsters at the origin of globular clusters

A team from the universities of Geneva, Paris and Barcelona has found strong evidence that supermassive stars can explain the anomalies observed in large clusters of stars.

Peer-Reviewed Publication

UNIVERSITÉ DE GENÈVE

Globular clusters are the most massive and oldest star clusters in the Universe. They can contain up to 1 million of them. The chemical composition of these stars, born at the same time, shows anomalies that are not found in any other population of stars. Explaining this specificity is one of the great challenges of astronomy. After having imagined that supermassive stars could be at the origin, a team from the Universities of Geneva and Barcelona, and the Institut d’Astrophysique de Paris (CNRS and Sorbonne University) believes it has discovered the first chemical trace attesting to their presence in globular proto-clusters, born about 440 million years after the Big Bang. These results, obtained thanks to observations by the James-Webb space telescope, are to be found in Astronomy and Astrophysics.

Globular clusters are very dense groupings of stars distributed in a sphere, with a radius varying from a dozen to a hundred light years. They can contain up to 1 million stars and are found in all types of galaxies. Ours is home to about 180 of them. One of their great mysteries is the composition of their stars: why is it so varied? For instance, the proportion of oxygen, nitrogen, sodium and aluminium varies from one star to another. However, they were all born at the same time, within the same cloud of gas. Astrophysicists speak of ‘‘abundance anomalies’’.

Monsters with very short lives

A team from the universities of Geneva (UNIGE) and Barcelona, and the Institut d’Astrophysique de Paris (CNRS and Sorbonne University) has made a new advance in the explanation of this phenomenon. In 2018, it had developed a theoretical model according to which supermassive stars would have «polluted» the original gas cloud during the formation of these clusters, enriching their stars with chemical elements in a heterogeneous manner. ‘‘Today, thanks to the data collected by the James-Webb Space Telescope, we believe we have found a first clue of the presence of these extraordinary stars,’’ explains Corinne Charbonnel, a full professor in the Department of Astronomy at the UNIGE Faculty of Science, and first author of the study.

These celestial monsters are 5 000 to 10 000 times more massive and five times hotter at their centre (75 million °C) than the Sun. But proving their existence is complex. ‘‘Globular clusters are between 10 and 13 billion years old, whereas the maximum lifespan of superstars is two million years. They therefore disappeared very early from the clusters that are currently observable. Only indirect traces remain,’’ explains Mark Gieles, ICREA professor at the University of Barcelona and co-author of the study.

Revealed by light

Thanks to the very powerful infrared vision of the James-Webb telescope, the co-authors were able to support their hypothesis. The satellite captured the light emitted by one of the most distant and youngest galaxies known to date in our Universe. Located at about 13.3 billion light-years, GN-z11 is only a few tens of millions of years old. In astronomy, the analysis of the light spectrum of cosmic objects is a key element in determining their characteristics. Here, the light emitted by this galaxy has provided two valuable pieces of information.

‘‘It has been established that it contains very high proportions of nitrogen and a very high density of stars,’’ says Daniel Schaerer, associate professor in the Department of Astronomy at the UNIGE Faculty of Science, and co-author of the study. This suggests that several globular clusters are forming in this galaxy and that they still harbour an active supermassive star. ‘‘The strong presence of nitrogen can only be explained by the combustion of hydrogen at extremely high temperatures, which only the core of supermassive stars can reach, as shown by the models of Laura Ramirez-Galeano, a Master’s student in our team,’’ explains Corinne Charbonnel.

These new results strengthen the international team’s model. The only one currently capable of explaining the abundance anomalies in globular clusters. The next step for the scientists will be to test the validity of this model on other globular clusters forming in distant galaxies, using the James-Webb data.

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JOURNAL

Astronomy and Astrophysics

DOI

10.1051/0004-6361/202346410 

METHOD OF RESEARCH

News article

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

N-enhancement in GN-z11: First evidence for supermassive stars nucleosynthesis in proto-globular clusters-like conditions at high redshift?

Tidal shocks can light up the remains of a star being pulled apart by a black hole

Peer-Reviewed Publication

UNIVERSITY OF TURKU

 

IMAGE: IN A TIDAL DISRUPTION EVENT, A STAR MOVES CLOSE ENOUGH TO A SUPERMASSIVE BLACK HOLE SO THAT THE GRAVITATIONAL PULL OF THE BLACK HOLE BENDS THE STAR UNTIL IT IS DESTROYED (IMAGE 1). THE STELLAR MATTER FROM THE DESTROYED STAR FORMS AN ELLIPTICAL STREAM AROUND THE BLACK HOLE (IMAGE 2). TIDAL SHOCKS ARE FORMED AROUND THE BLACK HOLE AS THE GAS HITS ITSELF ON ITS WAY BACK AFTER CIRCLING THE BLACK HOLE (IMAGE 3). THE TIDAL SHOCKS CREATE BRIGHT OUTBURSTS OF POLARISED LIGHT THAT CAN BE OBSERVED IN OPTICAL AND ULTRAVIOLET WAVELENGTHS. OVER TIME, THE GAS FROM THE DESTROYED STAR FORMS AN ACCRETION DISK AROUND THE BLACK HOLE (IMAGE 4) FROM WHERE IT IS SLOWLY PULLED INTO THE BLACK HOLE. THE SCALE OF THE IMAGE IS NOT ACCURATE. view more 

CREDIT: JENNI JORMANAINEN

The Universe is a violent place where even the life of a star can be cut short. This occurs when a star finds itself in a "bad" neighbourhood, specifically near a supermassive black hole.

These black holes weigh millions or even billions of times the mass of the Sun and typically reside in the centres of quiet galaxies. As a star moves closer to the black hole, it experiences the ever-increasing gravitational pull of the supermassive black hole until it becomes more powerful than the forces that keep the star together. This results in the star being disrupted or destroyed, an event known as a Tidal Disruption Event (TDE).

“After the star has been ripped apart, its gas forms an accretion disk around the black hole. The bright outbursts from the disk can be observed in nearly every wavelength, especially with optical telescopes and satellites that detect X-rays,” says Postdoctoral Researcher Yannis Liodakis from the University of Turku and the Finnish Centre for Astronomy with ESO (FINCA).

Until recently, researchers knew only of a few TDEs, as there were not many experiments capable of detecting them. In recent years, however, scientists have developed the necessary tools to observe more TDEs.  Interestingly, but perhaps not too surprisingly, these observations have led to new mysteries that the researchers are currently studying.

“Observations from large-scale experiments with optical telescopes have revealed that a large number of TDEs do not produce X-rays even though the bursts of visible light can be clearly detected. This discovery contradicts our basic understanding of the evolution of the disrupted stellar matter in TDEs,” Liodakis notes.

A study published in the journal Science by an international team of astronomers led by the Finnish Centre for Astronomy with ESO suggests that the polarised light coming from TDEs might hold the key to solving this mystery.

Instead of the formation of an X-ray bright accretion disk around the black hole, the observed outburst in the optical and ultraviolet light detected in many TDEs can arise from tidal shocks. These shocks form far away from the black hole as the gas from the destroyed star hits itself on its way back after circling the black hole. The X-ray bright accretion disk would form much later in these events. 

"Polarisation of light can provide unique information about the underlying processes in astrophysical systems. The polarised light we measured from the TDE could only be explained by these tidal shocks,” says Liodakis, who is the lead author of the study.

Polarised light helped researchers to understand the destruction of stars

The team received a public alert in late 2020 from the Gaia satellite of a nuclear transient event in a nearby galaxy designated as AT 2020mot. The researchers then observed AT 2020mot in a wide range of wavelengths including optical polarisation and spectroscopy observations conducted at the Nordic Optical Telescope (NOT), which is owned by the University of Turku. The observations conducted at the NOT were particularly instrumental in making this discovery possible. In addition, the polarisation observations were done as part of the observational astronomy course for high school students.

"The Nordic Optical Telescope and the polarimeter we use in the study have been instrumental in our efforts to understand supermassive black holes and their environments," says Doctoral Researcher Jenni Jormanainen from FINCA and the University of Turku who led the polarisation observations and analysis with the NOT.

The researchers found that the optical light coming from AT 2020mot was highly polarised and was varying with time. Despite several attempts, none of the radio or X-ray telescopes were able to detect radiation from the event before, during, or even months after the peak of the outburst.

“When we saw how polarised AT2020mot was, we immediately thought of a jet shooting out from the black hole, as we often observe around supermassive black holes that accrete the surrounding gas. However, no jet was there to be found,” says Elina Lindfors, an Academy Research Fellow at the University of Turku and FINCA.

The team of astronomers realised that the data most closely matched a scenario where the stream of stellar gas collides with itself and forms shocks near the pericenter and apocenter of its orbit around the black hole. The shocks then amplify and order the magnetic field in the stellar stream which will naturally lead to highly polarised light. The level of the optical polarisation was too high to be explained by most models, and the fact that it was changing over time made it even harder.

“All models we looked at could not explain the observations, except the tidal shock model,” notes Karri Koljonen, who was an astronomer at FINCA at the time of the observations and is now working at the Norwegian University of Science and Technology (NTNU).

The researchers will continue to observe the polarised light coming from TDEs and may soon discover more about what happens after a star is disrupted.

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JOURNAL

Science

DOI

10.1126/science.abj9570 

ARTICLE TITLE

Optical polarization from colliding stellar stream shocks in a tidal disruption event

ARTICLE PUBLICATION DATE

11-May-2023