New study suggests supermassive black holes could form from dark matter

Artist’s impression of a spiral galaxy embedded in a larger distribution of invisible dark matter, known as a dark matter halo (coloured in blue). Studies looking at the formation of dark matter haloes have suggested that each halo could harbour a very dense nucleus of dark matter, which may potentially mimic the effects of a central black hole, or eventually collapse to form one.Credit: ESO / L. Calçada.  Licence type:  Attribution (CC BY 4.0)

A new theoretical study has proposed a novel mechanism for the creation of supermassive black holes from dark matter. The international team find that rather than the conventional formation scenarios involving ‘normal’ matter, supermassive black holes could instead form directly from dark matter in high density regions in the centres of galaxies. The result has key implications for cosmology in the early Universe, and is published in Monthly Notices of the Royal Astronomical Society.

Exactly how supermassive black holes initially formed is one of the biggest problems in the study of galaxy evolution today. Supermassive black holes have been observed as early as 800 million years after the Big Bang, and how they could grow so quickly remains unexplained.

Standard formation models involve normal baryonic matter – the atoms and elements that that make up stars, planets, and all visible objects – collapsing under gravity to form black holes, which then grow over time. However the new work investigates the potential existence of stable galactic cores made of dark matter, and surrounded by a diluted dark matter halo, finding that the centres of these structures could become so concentrated that they could also collapse into supermassive black holes once a critical threshold is reached.

According to the model this could have happened much more quickly than other proposed formation mechanisms, and would have allowed supermassive black holes in the early Universe to form before the galaxies they inhabit, contrary to current understanding.

Carlos R. Argüelles, the researcher at Universidad Nacional de La Plata and ICRANet who led the investigation comments: “This new formation scenario may offer a natural explanation for how supermassive black holes formed in the early Universe, without requiring prior star formation or needing to invoke seed black holes with unrealistic accretion rates.”

Another intriguing consequence of the new model is that the critical mass for collapse into a black hole might not be reached for smaller dark matter halos, for example those surrounding some dwarf galaxies. The authors suggest that this then might leave smaller dwarf galaxies with a central dark matter nucleus rather than the expected black hole. Such a dark matter core could still mimic the gravitational signatures of a conventional central black hole, whilst the dark matter outer halo could also explain the observed galaxy rotation curves.

“This model shows how dark matter haloes could harbour dense concentrations at their centres, which may play a crucial role in helping to understand the formation of supermassive black holes,” added Carlos.

“Here we’ve proven for the first time that such core–halo dark matter distributions can indeed form in a cosmological framework, and remain stable for the lifetime of the Universe.”

The authors hope that further studies will shed more light on supermassive black hole formation in the very earliest days of our Universe, as well as investigating whether the centres of non-active galaxies, including our own Milky Way, may play host to these dense dark matter cores.

Source: Royal Astronomical Society (RAS)/News

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Media Contacts:

Dr Morgan Hollis
Royal Astronomical Society
Mob: +44 (0)7802 877 700
press@ras.ac.uk

Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)7802 877 699
press@ras.ac.uk

Science contacts

Dr Carlos R. Argüelles
Facultad de Ciencias Astronómicas y Geofísicas
Universidad Nacional de La Plata
Buenos Aires
Argentina
carguelles@fcaglp.fcaglp.unlp.edu.ar 

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Further information

The new work appears in, “On the formation and stability of fermionic dark matter haloes in a cosmological framework”, Carlos R Argüelles, Manuel I Díaz, Andreas Krut, and Rafael Yunis, Monthly Notices of the Royal Astronomical Society (2020), in press (DOI: 10.1093/mnras/staa3986).

A copy of the paper is available from: https://doi.org/10.1093/mnras/staa3986

The institutions participating in the research were Universidad Nacional de La Plata, the National Research Council of Science and Technology, the International Center for Relativistic Astrophysics Network, and Buenos Aires National University. 

Notes for editors

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 4,400 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.

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Big galaxies steal star-forming gas from their smaller neighbours

An artist’s impression showing the increasing effect of ram-pressure stripping in removing gas from galaxies, sending them to an early death. Credit: ICRAR, NASA, ESA, the Hubble Heritage Team (STScI/AURA)

Large galaxies are known to strip the gas that occupies the space between the stars of smaller satellite galaxies.

In research published today, astronomers have discovered that these small satellite galaxies also contain less ‘molecular’ gas at their centres.

Molecular gas is found in giant clouds in the centres of galaxies and is the building material for new stars. Large galaxies are therefore stealing the material that their smaller counterparts need to form new stars.

Lead author Dr Adam Stevens is an astrophysicist based at UWA working for the International Centre for Radio Astronomy Research (ICRAR) and affiliated to the ARC Centre of Excellence in All Sky Astrophysics in 3 Dimensions (ASTRO 3D).

Dr Stevens said the study provides new systematic evidence that small galaxies everywhere lose some of their molecular gas when they get close to a larger galaxy and its surrounding hot gas halo.

“Gas is the lifeblood of a galaxy,” he said.

“Continuing to acquire gas is how galaxies grow and form stars. Without it, galaxies stagnate.

“We’ve known for a long time that big galaxies strip ‘atomic’ gas from the outskirts of small galaxies.

“But, until now, it hadn’t been tested with molecular gas in the same detail.”

ICRAR-UWA astronomer Associate Professor Barbara Catinella said galaxies don’t typically live in isolation.

“Most galaxies have friends,” she says.

“And when a galaxy moves through the hot intergalactic medium or galaxy halo, some of the cold gas in the galaxy is stripped away.

“This fast-acting process is known as ram pressure stripping.”

Two viewing angles of a galaxy undergoing ram-pressure stripping in the IllustrisTNG simulation. Each column shows matter of a different form in the galaxy and its immediate surroundings. From left to right: (1) atomic gas; (2) molecular gas; (3) all gas; (4) stars; and (5) dark matter. Credit: Adam Stevens/ICRAR. Hi-res image

The research was a global collaboration involving scientists from the University of Maryland, Max Planck Institute for Astronomy, University of Heidelberg, Harvard-Smithsonian Center for Astrophysics, University of Bologna and Massachusetts Institute of Technology.

Molecular gas is very difficult to detect directly.

The research team took a state-of-the-art cosmological simulation and made direct predictions for the amount of atomic and molecular gas that should be observed by specific surveys on the Arecibo telescope in Puerto Rico and the IRAM 30-meter telescope in Spain.

They then took the actual observations from the telescopes and compared them to their original predictions.

The two were remarkably close.

Fly-through of galaxies having their gas stripped in the IllustrisTNG simulation.

Big galaxies steal star-forming gas from their smaller neighbours from ICRAR on Vimeo.

Associate Professor Catinella, who led the Arecibo survey of atomic gas, says the IRAM 30-meter telescope observed the molecular gas in more than 500 galaxies.

“These are the deepest observations and largest sample of atomic and molecular gas in the local Universe,” she says.

“That’s why it was the best sample to do this analysis.”

The team’s finding fits with previous evidence that suggests satellite galaxies have lower star formation rates.

Dr Stevens said stripped gas initially goes into the space around the larger galaxy.

“That may end up eventually raining down onto the bigger galaxy, or it might end up just staying out in its surroundings,” he said.

But in most cases, the little galaxy is doomed to merge with the larger one anyway.

“Often they only survive for one to two billion years and then they’ll end up merging with the central one,” Dr Stevens said.

“So it affects how much gas they’ve got by the time they merge, which then will affect the evolution of the big system as well.

“Once galaxies get big enough, they start to rely on getting more matter from the cannibalism of smaller galaxies.”

Original Publication:

‘Molecular hydrogen in IllustrisTNG galaxies: carefully comparing signatures of environment with local CO & SFR data’, published in Monthly Notices of the Royal Astronomical Society on February 23^rd, 2021.   Click here for the paper

Contacts:

Dr Adam Stevens (ICRAR / ASTRO 3D / UWA)

Ph: +61 8 6488 7627                E: Adam.Stevens@icrar.org

Associate Professor Barbara Catinella (ICRAR / UWA)

Ph: +61 8 6488 7760                E: Barbara.Catinella@icrar.org

Kirsten Gottschalk (Media Contact, ICRAR)

Ph: +61 438 361 876               E: Kirsten.Gottschalk@icrar.org

Jess Reid (Media Contact, University of Western Australia)

Ph: +61 8 6488 6876                E: Jess.Reid@uwa.edu.au

 

 Source: International Centre for Radio Astronomy Research (ICRAR)/News

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Supernova 1987A: Reclusive Neutron Star May Have Been Found in Famous Supernova

Supernova 1987A
Credit: Chandra (X-ray): NASA/CXC/Univ. di Palermo/E. Greco;
Illustration: INAF-Osservatorio Astronomico di Palermo/Salvatore Orlando

JPEG (150.1 kb) -Large JPEG (961.3 kb) - Tiff (18.9 MB) - More Images

Tour: Einstein's Theory of Relativity, Critical for GPS, Seen in Distant Stars - More Animations

 

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Astronomers have found evidence for the existence of a neutron star at the center of Supernova 1987A (SN 1987A), which scientists have been seeking for over three decades. As reported in our latest press release, SN 1987A was discovered on February 24, 1987. The panel on the left contains a 3D computer simulation, based on Chandra data, of the supernova debris from SN 1987A crashing into a surrounding ring of material. The artist's illustration (right panel) depicts a so-called pulsar wind nebula, a web of particles and energy blown away from a pulsar, which is a rotating, highly magnetized neutron star. Data collected from NASA's Chandra X-ray Observatory and NuSTAR in a new study support the presence of a pulsar wind nebula at the center of the ring. 

If this result is upheld by future observations, it would confirm the existence of a neutron star in SN 1987A, the collapsed core that astronomers expect would be present after the star exploded. The pulsar would also be the youngest one ever found. 

NuSTAR and Chandra images of Supernova 1987A

When a star explodes, it collapses onto itself before the outer layers are blasted into space. The compression of the core turns it into an extraordinarily dense object, with the mass of the Sun squeezed into an object only about 10 miles across. Neutron stars, as they were dubbed because they are made nearly exclusively of densely packed neutrons, are laboratories of extreme physics that cannot be duplicated here on Earth. Some neutron stars have strong magnetic fields and rotate rapidly, producing a beam of light akin to a lighthouse. Astronomers call these objects "pulsars," and they sometimes blow winds of charged particles that can create pulsar wind nebulas.

With Chandra and NuSTAR, the team found relatively low-energy X-rays from the supernova debris crashing into surrounding material. The team also found evidence of high-energy particles, using NuSTAR's ability to detect higher-energy X-rays.

 There are two likely explanations for this energetic X-ray emission: either a pulsar wind nebula, or particles being accelerated to high energies by blast wave of the explosion. The latter effect doesn't require the presence of a pulsar and occurs over much larger distances from the center of the explosion.

The latest X-ray study supports the case for the pulsar wind nebula on a couple of fronts. First, the brightness of the higher energy X-rays remained about the same between 2012 and 2014, while the radio emission increased. This goes against expectations in the scenario of energetic particles in the explosion debris. Next, authors estimate it would take almost 400 years to accelerate the electrons up to the highest energies seen in the NuSTAR data, which is over ten times older than the age of the remnant.

The Chandra and NuSTAR data also support a 2020 result from the Atacama Large Millimeter Array (ALMA) that provided possible evidence for the structure of a pulsar wind nebula in the radio band. While this "blob" had other potential explanations, its identification as a pulsar wind nebula could be substantiated with the new X-ray data.

The center of SN 1987A is surrounded by gas and dust. The authors used state-of-the-art simulations to understand how this material would absorb X-rays at different energies, enabling more accurate interpretation of the X-ray spectrum, that is, the spread of X-rays over wavelength. This enables them to estimate what the spectrum of the central regions of SN 1987A is without the obscuring material.

A paper describing these results is being published this week in The Astrophysical Journal and a preprint is available online. The authors of the paper are Emanuele Greco and Marco Miceli (University of Palermo in Italy), Salvatore Orlando, Barbara Olmi and Fabrizio Bocchino (Palermo Astronomical Observatory, a National Institute for Astrophysics, or INAF, research facility); Shigehiro Nagataki and Masaomi Ono (Astrophysical Big Bang Laboratory, RIKEN in Japan); Akira Dohi (Kyushu University in Japan), and Giovanni Peres (University of Palermo).

NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science from Cambridge Massachusetts and flight operations from Burlington, Massachusetts.

NuSTAR is a Small Explorer mission led by Caltech and managed by NASA's Jet Propulsion Laboratory for the agency's Science Mission Directorate in Washington. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corporation in Dulles, Virginia (now part of Northrop Grumman). NuSTAR's mission operations center is at UC Berkeley, and the official data archive is at NASA's High Energy Astrophysics Science Archive Research Center. ASI provides the mission's ground station and a mirror archive. JPL is a division of Caltech.

Quick Look: Supernova 1987A Pulsar Wind Nebula

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Fast facts for Supernova 1987A:

Category:  Supernovas & Supernova Remnants
Coordinates (J2000): RA 05h 35m 28.30s | Dec -69° 16´ 11.10"
Constellation:  Dorado
Observation Date: 7 pointings between Mar 2012 and Sept 2014
Observation Time: 95 hours 30 minutes (3 days 23 hours 30 minutes)
Obs. ID: 13735, 14417, 14697-14698, 15809-15810, 17415
Instrument:  ACIS
Also Known As: Supernova 1987A
References: Greco, E., et al., 2021, ApJ Letters (accepted)  arXiv:2101.0929
Distance Estimate About 168,000 light years

Source: NASA's Chandra X-ray Observatory

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VLA Helps Astronomers Make New Discoveries About Star-Shredding Events

Artist's conception of a Tidal Disruption Event (TDE) -- a star being shredded by the powerful gravity of a supermassive black hole. Material from the star spirals into a disk rotating around the black hole, and a jet of particles is ejected.  Credit: Sophia Dagnello, NRAO/AUI/NSF.Hi-res image

After the supermassive black hole tore the star apart, roughly half of the star debris was flung back out into space, as seen in this artist's conception, while the remainder formed a glowing accretion disc around the black hole. The system shone brightly across many wavelengths and is thought to have produced energetic, jet-like outflows perpendicular to the accretion disc. A central, powerful engine near the accretion disc spewed out these fast subatomic particles. Credit: DESY, Science Communication Lab. Hi-res image 

 

 

 

This animation shows how, as the star approaches the black hole, the enormous tidal forces stretch it more and more until it is finally shredded. Half of the stellar debris is flung back into space, while the remaining part forms a rotating accretion disk from which two strong outflows of matter shoot up and down. The system acts as a powerful natural particle accelerator. Credit: Animation by DESY, Science Communication Lab

Black holes that are millions or billions of times more massive than the Sun lurk at the cores of large galaxies and can have profound effects on their surroundings. One of the more exciting of those effects comes when a star ventures too close to the black hole and falls victim to that monster’s powerful gravitational pull. The star is shredded by tidal forces in a process colorfully termed spaghettification.

When that happens, some of the star’s material is pulled into a disk that orbits the black hole, heating rapidly and launching jets of fast-moving particles outward in two opposite directions. This produces an outburst that can be observed with a variety of telescopes, including radio, visible, ultraviolet, and X-ray instruments.

Over the past couple of decades, astronomers have seen a number of outbursts that they have concluded are either the star-shredding Tidal Disruption Events (TDEs) or candidates for such events. In 2018, astronomers used the National Science Foundation’s Very Long Baseline Array (VLBA) to directly image the formation and expansion of a jet coming from a TDE.

The 22 February edition of Nature Astronomy includes reports on observations of two different TDEs, each of which adds to our knowledge of these phenomena but also raises new questions for scientists to tackle. The NSF’s Karl G. Jansky Very Large Array (VLA) was used to study both of these events, occurring in 2015 and 2019 respectively.

One of these star-shredding events is the first known to produce a high-energy neutrino — an elusive subatomic particle moving at nearly the speed of light. The other is the first seen to emit flares of radio waves long after the initial event. Both discoveries are forcing astronomers to rethink their explanations for some of the processes involved in TDEs.

The neutrino-producing TDE, called AT2019dsg, was discovered on 9 April 2019 by the Zwicky Transient Facility (ZTF), a robotic optical telescope at the Palomar Observatory in California. Astronomers subsequently observed it with the VLA, NASA’s Neil Geherels Swift Observatory, and the European Space Agency’s XMM-Newton. They found that it occurred in a galaxy called 2MASX J20570298+1412165, more than 690 million light-years from Earth in the constellation Delphinus.

On 1 October, 2019, the NSF’s IceCube Neutrino Observatory in Antarctica detected a high-energy neutrino that came from the same region of sky as the April TDE. Neutrinos are pervasive throughout the universe but are extremely difficult to detect because they very rarely interact with other matter. In fact, this is only the second high-energy neutrino to be linked to an object outside our Milky Way galaxy. The detection was surprising because astronomers had expected that if TDEs produced such neutrinos it would happen relatively soon after the start of the event.

“Astrophysicists have long theorized that tidal disruptions could produce high-energy neutrinos, but this is the first time we’ve actually been able to connect them with observational evidence,” said Robert Stein, a doctoral student at the German Electron-Synchrotron (DESY) research center in Zeuthen, Germany, and Humboldt University in Berlin. “But it seems like this particular event, called AT2019dsg, didn’t generate the neutrino when or how we expected. It’s helping us better understand how these phenomena work.”

The other TDE, called ASASSN-15oi, was discovered at visible-light wavelengths by the All-Sky Automated Survey for SuperNovae (ASASSN) on 14 August 2015, in a galaxy more than 700 million light-years from Earth. Astronomers began observing it with the VLA eight days after its discovery, expecting to detect radio emission in the early stages of the event. Instead, they saw no radio emission from the object until six months later, in February of 2016.

In addition, they later learned that the ongoing VLA Sky Survey observed the region in July of 2019 and found evidence of another radio flare then, nearly four years after the initial event. The astronomers called the two delayed flares “a new puzzling phenomenon in TDEs.”

“Flares with such delays have not been observed before. Moreover, the delayed flares exhibit peculiar properties currently not supported by theories of TDE radio emission,” said Assaf Horesh, of the Hebrew University of Jerusalem.

In both cases, the researchers look forward to studying future TDEs for clues that can help resolve the new mysteries their work has unveiled. These dramatic events are an excellent example of how we can advance our understanding of the universe through multimessenger astronomy — studies that use electromagnetic radiation (visible light, radio waves, ultraviolet, etc.), particles such as neutrinos, and even gravitational waves — ripples in spacetime — to learn how cosmic objects work.

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Link to TDE Neutrino paper

Link to Delayed Radio Flares pape

Source:  National Radio Astronomy Observatory (NRAO)/News

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ALMA reveals the very seeds of stars in the forming for the first time

Core “G205.46-14.56M3” located in the Orion Molecular Cloud shows signs of multiple small blobs inside. Top right insert: SCUBA-2 image of G2-5.46-14.56M3 as observed by the JCMT, Hawaii. Bottom right insert: ALMA resolves the newly forming stars within. Credit: ASIAA/Wei-Hao Wang/ALMA (ESO/NAOJ/NRAO)/Tie Liu/Sahu et al.Hi-res image

Stars are known to form in so-called “molecular clouds”; collections of cold gas and dust in the space between stars. These stellar nurseries can contain a number of dense clumps of gas and dust called“ prestellar cores". Research has suggested that these cores are expected to exhibit concentrated structures within them - the “seeds” of new stars right at the cusp of being born.

Strong efforts by astronomers have been made to find such “seeds” of stars inside prestellar cores in the past, but mostly in vain. It was difficult to catch such seeds in action perhaps because they are short-lived, but also due to the inherent difficulties in observing such dense regions and at such small scales.

Despite the challenges, Dipen Sahu, at the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), Taiwan, and lead author of this study stated that “it is very important to understand when and how such stellar embryo(s) come to live” noting that “it is this critical early stage that is important to observe as we understand how these early stages shape the stellar offspring. We would like to know how stellar systems are formed, but we need to study them near their birth to fully understand the process.”

One of the closest, brightest and most well known stellar nurseries can be found in the constellation of Orion also known as the “Hunter”. The international team, including astronomers from Taiwan, China, Japan, and Korea, first started out to uncover cold and dense cores in the Orion Molecular Cloud. As dust in the cores absorbs light and blocks the view at the optical wavelengths, astronomers make use of "light" emitted by the dust inside the dense cores at submillimeter wavelengths, obtained using such telescopes as the James Clark Maxwell Telescope (JCMT) situated on the slopes of Maunakea in Hawaii.

“The JCMT continues to play a pivotal role in locating these cores!”, says Tie Liu at Shanghai Astronomical Observatory, co-author of this study and the principal investigator of the ALMA observation program, “the JCMT is critical in that it gives us the speed to hunt around these stellar nurseries with the sensitivity needed to find these faint regions of cold and dense gas”.

With JCMT providing the team with stellar nursery candidates, the team turned to the largest telescope on the ground to date, the Atacama Large Millimeter and submillimeter Array (ALMA) located in the high desert in northern Chile. The observations carried out with ALMA in late 2018 to early 2019 unveil to the team five cores with a very concentrated gas and dust distribution at a scale of a 1000 AU. Toward one core named “G205.46-14.56M3” in particular, the image shows signs of multiple small peak structures inside. These peaks are estimated to harbor a high density of cold gas that has never been seen before and their significant mass makes astronomers think that they are very likely to form a binary star system in the future. It is known that a large fraction of Sun-like stars are in binary or multiple stellar systems.

Sheng-Yuan Liu at ASIAA, co-author of this study stated “ALMA provides us with unprecedented sensitivity and angular resolution so that we can see faint sources with truly sharp images. Finding twins or triplets should be common in stellar nurseries but it is remarkable to actually obtain the image like seeing inside an egg with two yolks!”

It remains unclear what leads to the sub-structures we see in the core of G205.46-14.56M3. The substructures are likely a complicated interplay between the gas motion, gravity, and magnetic fields that are threading through the gas. The observed emission from the dust only tells us how gas and dust are distributed. Understanding how the gas is moving and how magnetic fields are distributed inside such cores would allow astronomers to further pinpoint the decisive process.

“Detecting such a handful of stellar seeds is just the beginning. I am excited to see what new discoveries we will make when we combine the power of both JCMT and future followup studies with ALMA”, says Dipen Sahu.

More Information:

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organization for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

This research presented in a paper “ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Detection of Extremely High-density Compact Structure of Prestellar Cores and Multiple Substructures Within,” by Sahu et al. has appeared in the Astrophysical Journal Letters on Jan. 19th., 2021.

The team is composed of Dipen Sahu (Academia Sinica Institute of Astronomy and Astrophysics), Sheng-Yuan Liu (Academia Sinica Institute of Astronomy and Astrophysics), Tie Liu (Shanghai Astronomical Observatory, Chinese Academy of Sciences), Neal J. Evans II (Department of Astronomy The University of Texas at Austin), Naomi Hirano (Academia Sinica Institute of Astronomy and Astrophysics), Ken'ichi Tatematsu (Nobeyama Radio Observatory, National Astronomical Observatory of Japan, National Institutes of Natural Sciences), Chin-Fei Lee(Academia Sinica Institute of Astronomy and Astrophysics), Kee-Tae Kim (Korea Astronomy and Space Science Institute), Somnath Dutta (Academia Sinica Institute of Astronomy and Astrophysics), Dana Alina (Department of Physics, School of Sciences and Humanities, Nazarbayev University)

Media Contact:

• • Dr. Sheng-Yuan Liu 

    Email: syliu@asiaa.sinica.edu.tw

Tel: +886 2 2366 5440

 

Source:  Academia Sinica Institute of Astronomy and Astrophysics (ASIAA)

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A Long Wavelength Look at Distant Quasar Hosts

An artist’s impression of a quasar
Credit: NASA, ESA and J. Olmsted (STScI) - Hi-res Image

Some quasar host galaxies live in the early universe. This makes them especially interesting, since they had to have accumulated a lot of mass very quickly. Luckily for us, radio telescopes like ALMA can peer back in time and tell us more about these galaxies and their environments.

Finding Far-Off Quasars

Quasars are absurdly energetic objects. They are a version of the supermassive black holes at the centers of galaxies, and what makes them unique is the large amounts of energy they emit while actively accreting material. A significant portion of this energy is emitted as short-wavelength ultraviolet (UV) light, which is the key to studying quasars that live in the early universe.

The farther away an object is, the more its light becomes redshifted as it travels to us — that is, the wavelength at which light from the object was first emitted is shorter than the wavelength we observe when that light reaches us. So in the case of far-off quasars, their UV emission will be redshifted into radio wavelengths, where we can still observe it!

In a recent study, a group of researchers led by Bram P. Venemans (Max-Planck Institute for Astronomy, Germany) used radio observations of distant quasar host galaxies to learn more about them, as well as conditions in the early universe.

FIR (left) and [C II] (right) emission maps (distances shown in arcseconds) for two galaxies from this study. The redder regions indicate higher emission levels; bluer regions point to the absence of emission. [Adapted from Venemans et al. 2020]

Evidence from Emissions 

All 27 galaxies in this study live at a redshift of roughly z = 6, or when the universe was just under a billion years old. Venemans and collaborators were especially interested in two types of emission from these galaxies: singly ionized carbon ([C II]) emission, which tracks the gas of the interstellar medium; and the general continuum brightness in the far-infrared (FIR), which is associated with dust. The spatial extent of the [C II] emission in particular is also sensitive to the motions of a galaxy and its surroundings.

The galaxies were observed by Atacama Large Millimeter/submillimeter Array (ALMA) in September 2019. The observations had a resolution of roughly a kiloparsec (or 19 trillion miles), which is pretty high definition for the early universe! This allowed Venemans and collaborators to examine the central regions of their galaxies. They were also able to probe the surrounding space for any companion galaxies.

Star formation rates versus distance from galaxy center. Each track represents a quasar host galaxy, with the color of the track corresponding to the FIR brightness of the galaxy. [Venemans et al. 2020]

Seeing into the Center 

It turned out that for the galaxies in this study, the central dust regions mapped closely onto the positions of central supermassive black holes. This may not sound like a profound observation, but it is observational evidence to support that these central black holes live at the hearts of dark matter halos, which are cosmological building blocks.

The [C II] emission revealed that about half of the quasar-hosting galaxies in this sample had companions. The FIR emission also allowed Venemans and collaborators to determine that in the central regions of their galaxies, star formation peaks at the center and then declines moving outward. The outer regions of these distant galaxies currently remain elusive, but as Venemans and collaborators noted, ALMA is quite capable of probing these galaxies further!

Citation:

“Kiloparsec-scale ALMA Imaging of [C II] and Dust Continuum Emission of 27 Quasar Host Galaxies at z ~ 6,” Bram P. Venemans et al 2020 ApJ 904 130. doi:10.3847/1538-4357/abc563

 By Tarini Konchady

 

Source: American Astronomical Society (AAS/NOVA)

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First black hole ever detected is more massive than we thought

An artist’s impression of the Cygnus X-1 system. This system contains the most massive stellar-mass black hole ever detected without the use of gravitational waves, weighing in at 21 times the mass of the Sun. Credit: International Centre for Radio Astronomy Research. Credit: International Centre for Radio Astronomy Research. Hi-res image

New observations of the first black hole ever detected have led astronomers to question what they know aboeut the Universe’s most mysterious objects.

Published today in the journal Science, the research shows the system known as Cygnus X-1 contains the most massive stellar-mass black hole ever detected without the use of gravitational waves.

Cygnus X-1 is one of the closest black holes to Earth. It was discovered in 1964 when a pair of Geiger counters were carried on board a sub-orbital rocket launched from New Mexico.

The object was the focus of a famous scientific wager between physicists Stephen Hawking and Kip Thorne, with Hawking betting in 1974 that it was not a black hole. Hawking conceded the bet in 1990.

In this latest work, an international team of astronomers used the Very Long Baseline Array—a continent-sized radio telescope made up of 10 dishes spread across the United States—together with a clever technique to measure distances in space.

“If we can view the same object from different locations, we can calculate its distance away from us by measuring how far the object appears to move relative to the background,” said lead researcher, Professor James Miller-Jones from Curtin University and the International Centre for Radio Astronomy Research (ICRAR).

“If you hold your finger out in front of your eyes and view it with one eye at a time, you’ll notice your finger appears to jump from one spot to another. It’s exactly the same principle.”

Astronomers observed the Cygnus X-1 system from different angles using the orbit of the Earth around the Sun to measure the perceived movement of the system against the background stars. This allowed them to refine the distance to the system and therefore the mass of the black hole. Credit: International Centre for Radio Astronomy Research. Hi-res image

“Over six days we observed a full orbit of the black hole and used observations taken of the same system with the same telescope array in 2011,” Professor Miller-Jones said. “This method and our new measurements show the system is further away than previously thought, with a black hole that’s significantly more massive.”

Co-author Professor Ilya Mandel from Monash University and the ARC Centre of Excellence in Gravitational Wave Discovery (OzGrav) said the black hole is so massive it’s actually challenging how astronomers thought they formed.

An artist’s impression of the Cygnus X-1 system. A stellar-mass black hole orbits with a companion star located 7,200 light years from Earth. Credit: International Centre for Radio Astronomy Research. Hi-res image

“Stars lose mass to their surrounding environment through stellar winds that blow away from their surface. But to make a black hole this heavy, we need to dial down the amount of mass that bright stars lose during their lifetimes” he said.

“The black hole in the Cygnus X-1 system began life as a star approximately 60 times the mass of the Sun and collapsed tens of thousands of years ago,” he said. “Incredibly, it’s orbiting its companion star—a supergiant—every five and a half days at just one-fifth of the distance between the Earth and the Sun.

“These new observations tell us the black hole is more than 20 times the mass of our Sun—a 50 per cent increase on previous estimates.”

Recent observations show the black hole in the Cygnus X-1 system is 21 times the mass of the Sun—a 50 per cent increase on previous estimates. To form such a massive black hole, astronomers had to revise their estimates of how much mass stars lose via stellar winds. Credit: International Centre for Radio Astronomy Research. Hi-res image

Xueshan Zhao is a co-author on the paper and a PhD candidate studying at the National Astronomical Observatories—part of the Chinese Academy of Sciences (NAOC) in Beijing.

“Using the updated measurements for the black hole’s mass and its distance away from Earth, I was able to confirm that Cygnus X-1 is spinning incredibly quickly—very close to the speed of light and faster than any other black hole found to date,” she said.

“I’m at the beginning of my research career, so being a part of an international team and helping to refine the properties of the first black hole ever discovered has been a great opportunity.”

CYGNUS X-1: the most massive black hole near to Earth from ICRAR on Vimeo.

 

More Information:

The International Centre for Radio Astronomy Research (ICRAR) is a joint venture between Curtin University and The University of Western Australia with support and funding from the State Government of Western Australia.

Original Publication:

‘Cygnus X-1 contains a 21-solar mass black hole – implications for massive star winds’, published in Science on February 18^th, 2021.

Companion Papers:

‘Reestimating the Spin Parameter of the Black Hole in Cygnus X-1’, published in The Astrophysical Journal on February 18th, 2021.

‘Wind mass-loss rates of stripped stars inferred from Cygnus X-1’, published in The Astrophysical Journal on February 18th, 2021.

Contacts:

Professor James Miller-Jones (ICRAR / Curtin University)

Ph: +61 488 484 825                        E: James.Miller-Jones@icrar.org

Professor Ilya Mandel (OzGrav / Monash University)

Ph: +61 8 466 710 590                     E: Ilya.Mandel@monash.edu

Pete Wheeler — Media Contact, ICRAR

Ph: +61 423 982 018                        E: Pete.Wheeler@icrar.org

Lauren Sydoruk (Media Contact, Curtin University)

Ph: +61 401 103 373                       E: Lauren.Sydoruk@curtin.edu.au

  

Source: International Centre for Radio Astronomy Research   ICRAR/News

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Hubble Views a Baby Star’s Tantrums

HH46 and HH47

Herbig-Haro objects are some of the rarer sights in the night sky, taking the form of thin spindly jets of matter floating among the surrounding gas and stars. The two Herbig-Haro objects cataloged as HH46 and HH47, seen in this image taken with the NASA/ESA Hubble Space Telescope, were spotted in the constellation of Vela (the Sails), at a distance of over 1,400 light-years from Earth. Prior to their discovery in 1977 by the American astronomer R. D. Schwartz, the exact mechanism by which these multi-colored objects formed was unknown.

It had been theorized that a Herbig-Haro object could be a type of reflection nebula – a nebula that does not emit light of its own, but shines because starlight is scattered or reflected off its dust cloud. Another theory suggested that it was a type of shock wave formed when winds emitted from a star interact with the surrounding matter. The mystery was finally solved when a protostar, unseen in this image, was discovered at the center of the long jets of matter in HH46 and HH47. The outflows of matter, some 10 light-years across, were ejected from the newly born star and violently propelled outwards at speeds of over 93 miles (150 kilometers) per second. Upon reaching the surrounding gas, the collision created the bright shock waves seen here.

Text credit: European Space Agency (ESA)
Image credit: ESA/Hubble & NASA, B. Nisini

Media Contact:

Claire Andreoli
NASA’s Goddard Space Flight Center, Greenbelt, Md.
(301) 286-1940

Editor: Lynn Jenner

 

Source: NASA/Solar System and Beyond

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A Map of a Stellar Explosion

This composite, false-color image reveals an explosive outflow of molecular gas within the Orion Nebula. A new study explores another such explosion and examines how it relates to the birth of massive stars.  Credit: ALMA/ESO/NAOJ/NRAO/. Bally/H. Drass et al.

There’s still much we don’t know about the birth of massive stars — stars with more than 8 times the mass of the Sun. A recent study reveals details of a thousand-year-old explosion that might provide clues about the formation of these giants.

 

The clouds of molecular gas in regions like the Orion nebula provide nurseries in which massive stars form and evolve. Credit:ESO/G. Beccari

 An Unexpected Explosion

Several decades ago, astronomers discovered something odd. In a region inside the Orion nebula where massive star formation is underway, scientists detected signs of an explosive outflow: dense molecular gas streaming outward from a central point at rapid speeds. Surprisingly, there was nothing at the center of this explosion.

This one-off discovery was intriguing. One could imagine a number of sudden, energy-liberating events that could occur in a massive star-forming environment — like the formation of a close massive stellar binary, or the merger of two young, massive protostars. And the discovery of several candidate runaway stars at the fringes of the explosion provided another hint to a dynamical origin.

Could this explosion help us understand the process of how massive stars form in their birth environments? Or was it just a fluke event? As years passed without astronomers finding evidence of another, similar outflow, these questions remained unanswered.

This ALMA SiO map of the star-forming region G5.89 shows outflowing molecular gas surrounding an expanding, shell-like HII region (white contours). Two stars moving away from the origin are marked in magenta and cyan. Credit: Adapted from Zapata et al. 2020

Two of Kind 

Forty years later, we now have proof of another such explosive outflow in a massive star-forming environment. In a recent publication led by Luis Zapata (UNAM Radio Astronomy and Astrophysics Institute, Mexico), a team of scientists has used the Atacama Large Millimeter/submillimeter Array (ALMA) to confirm the presence of streamers of molecular gas flowing isotropically outward from a central point in the massive stellar birthplace G5.89, which lies roughly 10,000 light-years away from us.

Zapata and collaborators measured 34 molecular filaments in this explosive outflow, finding that the streamers are accelerating as they expand outward. This is consistent with behavior of the Orion explosion and shows that the density of the ejecta is substantially larger than the surrounding medium.

As with the Orion explosive outflow, the point of origin of the filaments contains no source. Previous studies, however, have identified several young, massive stars in the periphery of the G5.89 explosion that are speeding away from the point of origin at roughly the right speed to have been at the center 1,000 years previously at the time of explosion.

A protostar lies embedded in a disk of gas and dust in this visualization. The collision of two protostars could release enough energy to power an explosive molecular outflow — and produce a massive star. Credit: NASA’s Goddard SFC

 Learning about Stellar Birth

What does all this tell us about the origins of massive stars? Explosive outflows like this — caused by dynamical interactions during the birth of massive stars — may be more common than we previously thought!

The authors estimate a rate for such outflows based on our limited observations, finding that there should be one every ~100 years. The fact that this is very close to the rate of supernovae further solidifies the connection of explosive molecular outflows to massive star formation.

Dedicated, high-sensitivity searches for more such outflows in nearby massive star-forming regions will certainly go a long way toward confirming this theory. In the meantime, the authors argue, we should consider revising high-mass star formation models to include dynamical interactions, as these stellar explosions may prove to be regular occurrences!

Bonus

The animation below shows a different view of the authors’ ALMA-observed streamers, traced by CO gas. Two axes give the position of observations, while the third axis and the colors show the radial velocity at each point in the streamers, showing how the ejecta are accelerating as they expand outward. The star marks the origin of the explosive outflow.

Citation

“Confirming the Explosive Outflow in G5.89 with ALMA,” Luis A. Zapata et al 2020 ApJL 902 L47. doi:10.3847/2041-8213/abbd3f

By Susanna Kohler

Source: American Astronomical Society/NOVA

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The Smallest Galaxies in Our Universe Bring More About Dark Matter to Light

A schematic of dark matter distributions where red indicates regions with higher dark matter density. The illustration on the left indicates that dark matter distribution becomes denser in the center of the galaxy, as this study found, whereas the illustration on the right shows a less dense distribution of dark matter according to SIDM. ©Kohei Hayashi

Our universe is dominated by a mysterious matter known as dark matter. Its name comes from the fact that dark matter does not absorb, reflect or emit electromagnetic radiation, making it difficult to detect.

Using stellar kinematics, a team of researchers has investigated the strength of dark matter scattered across the smallest galaxies in the universe.

"We discovered that the strength of dark matter is quite small, suggesting that dark matter does not easily scatter together," said professor Kohei Hayashi, lead author of the study.

Much is unknown about dark matter, but theoretical and experimental research, from particle physics to astronomy, are elucidating more about it little by little.

One prominent theory surrounding dark matter is the "self-interacting dark matter (SIDM) theory." It purports that dark matter distributions in galactic centers become less dense because of the self-scattering of dark matter.

However, supernova explosions, which occur toward the end of a massive star's life, can also form less dense distributions. This makes it challenging to distinguish whether it is the supernova explosion or the nature of dark matter that causes a less dense distribution of dark matter.

To clarify this, Hayashi and his team focused on ultra-faint dwarf galaxies. Here few stars exist, rendering the influences of supernova explosions negligible.

Their findings showed that dark matter is dense at the center of the galaxy, challenging the basic premise of SIDM. Images from the dwarf galaxy Segue 1 revealed high dark matter density at the center of the galaxy and limited scattering.

A graph indicating the strength of dark matter scattering (y-axis) versus the average relative velocity between dark matter and itself (x-axis). Error bars indicate galaxy estimates by previous studies, whereas the red regions shows results from the Segue 1 ultra-faint dwarf galaxy. © Hayashi et al.

"Our study showed how useful stellar kinematics in ultra-faint dwarf galaxies are for testing existing theories on dark matter," noted Hayashi. "Further observations using next-generation wide-field spectroscopic surveys with the Subaru Prime Focus Spectrograph, will 

Publication Details:

Title: Probing Dark Matter Self-interaction with Ultra-faint Dwarf Galaxies
Authors: Kohei Hayashi, Masahiro Ibe, Shin Kobayashi, Yuhei Nakayama, Satoshi Shirai
Journal: Physical Review D
DOI: 10.1103/PhysRevD.103.023017

Contact 

Kohei Hayashi
Astronomical Institute, Tohoku University
Email: k.hayasi@astr.tohoku.ac.jp
Website: https://www.astr.tohoku.ac.jp/en/index.html

 

Source:Tohoku University/Press

Press release in Japanese

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Flipped-Over Exoplanets Prove New Disk-Tilt Mechanism

Figure 1: Conceptual illustration of the exoplanetary system K2-290. The central star (center) has two planets and a companion star (upper right). The two planets orbit around the central star in nearly the opposite direction to the star's spin. The innermost planet, about 75% the size of Neptune, orbits the star every nine days. The larger, Jupiter sized planet, requires more than 48 days for a round trip, still faster than Mercury in our own system with its 88 day orbit. (Credit: Christoffer Grønne/Aarhus University). Hi-res image

An international team including astronomers from Tokyo Institute of Technology and Aarhus University discovered evidence that in some cases protoplanetary disks, gas and dust disks surrounding young stars in which planets form, may have been flipped over, resulting in backwards or retrograde orbits of the planets. This finding is an important step in understanding planet formation and orbital evolution.

In the Solar System, the eight planets orbit in the same direction, this is also the same direction that the Sun rotates. Over the last decade researchers discovered that this is not always the case with exoplanets, planets which orbit around stars other than the Sun. Some exoplanets have orbits tilted wildly away from the rotation of the star. Some even have orbits tipped over backwards with respect to the central star. The mechanisms by which this wide diversity of orbits come to be is an important question in modern astronomy.

In one possible mechanism, while the planets are still forming in a protoplanetary disk of gas and dust around a young star, the gravity of a nearby companion star can tilt the disk so that the planets form on misaligned orbits from the beginning. Here, ‘nearby’ means within about a light-year. This disk-tilt mechanism was first proposed in 2012, but no confirmed examples had been observed until now.

The exoplanetary system, K2-290, is an ideal laboratory to test this disk-tilt mechanism. It has a nearby companion star identified by the Subaru Telescope (Note 1). It also has two planets with coplanar orbits, orbits that are aligned with each other. The presence of two planets with similar orbits is important because it rules out scenarios where interactions between the planets cause the orbits to tilt.

The team including Dr. Teruyuki Hirano (Tokyo Institute of Technology/National Institutes of Natural Sciences) and Dr. Maria Hjorth (Aarhus University/Tokyo Institute of Technology) used the Subaru Telescope and other telescopes (Note 2) to measure the misalignment between the orbits of the planets and the central star. They found that the planet’s orbits have flipped over nearly backwards. Numerical simulations by the team showed that the companion would have been able to flip over the protoplanetary disk, imparting retrograde orbits on the resulting planets. This provides strong evidence that the disk-tilt mechanism could be responsible for misaligned orbits, not just in this case, but in other exoplanet systems as well. It is no longer safe to assume that planetary orbits are initially aligned with the rotation of the star just after the formation of the planets in their disk. While other theories to explain spin-orbit misalignments in exoplanet systems tend to work best on large, Jupiter-like planets in short period orbits, the disk-tilt mechanism applies to planets of any size; even potentially habitable Earth-sized planets.


These results appeared as Hjorth et. al. "A backward-spinning star with two coplanar planets" in the Proceedings of the National Academy of Sciences of the United States of America on February 15, 2021.

References:

Note 1: The companion star was discovered in 2018 using IRCS on the Subaru Telescope. The result appeared as Hjorth et al. "K2-290: a warm Jupiter and a mini-Neptune in a triple-star system" in Monthly Notices of the Royal Astronomical Society on January 15, 2019.

Note 2: The observations were made in 2019 using three high-dispersion spectrographs: HDS on the Subaru Telescope, HARPS-N on the Telescopio Nazionale Galileo, and ESPRESSO on the VLT. The alignments between the two planets' orbits and the star's rotation were measured using the Rossiter-McLaughlin (RM) effect. See "Inclined Orbits Prevail in Exoplanetary Systems" (press release on January 12, 2011) for other examples of misaligned exoplanet systems measured with the RM effect.

Relevant Links

• A backward-spinning star with two coplanar orbiting planets in a multi stellar system (Aarhus University, February 15, 2021 Press Release)
• Two backward orbiting exoplanets in a triple stellar system prove protoplanetary disk-tilt mechanism (Telescopio Nazionale Galileo, February 15, 2021 Press Release)

 

 Source: Subaru Telescope

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