It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Wednesday, January 18, 2023
Shift to ultraviolet-driven chemistry in planet-forming disks marks beginning of late-stage planet formation
The chemistry of planet formation has fascinated researchers for decades because the chemical reservoir in protoplanetary discs—the dust and gas from which planets form—directly impacts planet composition and potential for life.
New research from the University of Michigan Department of Astronomy suggests that chemistry in late-stage planet development is fueled by ultraviolet rays, rather than cosmic rays or X-rays, and this new understanding provides a chemical signature that helps researchers trace exoplanets back to their cosmic nurseries in the planet-forming disks.
Jenny Calahan, a doctoral student in astronomy and first author of the paper, which appears in Nature Astronomy, said the discovery was part happy accident, part building on previous work.
"It has been shown that there are bright, complex organic molecules present in the coldest and densest parts of planet-forming disks," Calahan said. "This bright emission has been puzzling because we expect these molecules to be frozen out at these temperatures, not in the gas where we can observe them."
These molecules are emitting from regions that are minus-400 degrees Fahrenheit, and at these temperatures they're thought to be frozen onto tiny solids that astronomers label as dust grains, or for the later mm-to-cm-sized solids as pebbles. These molecules should add to an icy coating on the grains, so they cannot be observed in the gas.
The planet-forming disk has three main components, a pebble-rich dusty midplane, a gas atmosphere and a small dust population coupled to the gas. As the planet-forming disk evolves over time, the changing environment affects the chemistry within. To account for the observed brightness, Calahan adjusted her model to decrease the mass of the small dust population—which typically blocks UV photons––to allow more UV photons to penetrate deep into these coldest regions of the disc. This reproduced the observed brightness.
"If we have a carbon-rich environment paired with a UV-rich environment due to the evolution of the small solids in planet forming regions, we can produce complex organics in the gas and reproduce these observations," she said.
This represents the evolution of small dust over time.
About 20 years ago, researchers realized that the chemistry of the gaseous disk is governed by chemistry operating on shorter timescales and powered by sources such as cosmic rays and X-rays, said Edwin Bergin, principal investigator, professor and chair of astronomy.
"Our new work suggests that what really matters is the ultraviolet radiation field generated by the star accreting matter from the disk," he said. "The initial steps in making planets, forming larger and larger solids, shifts the chemistry from cosmic rays and X-ray-driven early, to UV-driven during the phase where giant planets are thought to be born.
"Jenny's work tells us for terrestrial worlds, if you wonder how they get things like water, the key part of the evolution is the early phases before this shift occurs. That is when the volatile molecules that comprise life––carbon, hydrogen, nitrogen––are implanted in solids that make Earth-like worlds. These planets are not born in this phase but rather the composition of solids becomes fixed. The later stages of this model tells us how to determine the composition of material that makes giant planets."
Co-authors include: Arthur Bosman and Evan Rich, both of the U-M Department of Astronomy.
IMAGE: IN JUNE 2021, NASA’S JUNO SPACECRAFT FLEW CLOSE TO GANYMEDE, JUPITER’S LARGEST MOON, OBSERVING EVIDENCE OF MAGNETIC RECONNECTION. AN SWRI-LED TEAM USED JUNO DATA TO CHARACTERIZE THE MAGNETIC TOPOLOGY AND ELECTRON FLOW DIRECTION FOR TWO DIFFERENT RECONNECTION SCENARIOS AT GANYMEDE’S MAGNETOPAUSE. THE YELLOW DASHED LINE INDICATES JUNO’S TRAJECTORY.view more
CREDIT: SWRI/JIA ET AL. (2008)
SAN ANTONIO — Jan. 10, 2023 — In June 2021, NASA’s Juno spacecraft flew close to Ganymede, Jupiter’s largest moon, observing evidence of magnetic reconnection. A team led by Southwest Research Institute used Juno data to examine the electron and ion particles and magnetic fields as the magnetic field lines of Jupiter and Ganymede merged, snapped and reoriented, heating and accelerating the charged particles in the region.
“Ganymede is the only moon in our solar system with its own magnetic field,” said Juno Principal Investigator Dr. Scott Bolton of SwRI. “The snapping and reconnecting of Ganymede’s magnetic field lines with Jupiter’s creates the magnetospheric fireworks.”
Magnetic reconnection is an explosive physical process that converts stored magnetic energy into kinetic energy and heat. Ganymede’s mini magnetosphere interacts with Jupiter’s massive magnetosphere, in the magnetopause, the boundary between the two regions.
“We interpreted the presence of accelerated electrons traveling along the magnetic field at Ganymede’s magnetopause as evidence that magnetic reconnection was occurring there during the Juno flyby,” said Dr. Robert Ebert, lead author of a Geophysical Research Letters paper describing the findings. “These observations further support the notion that magnetic reconnection at Ganymede’s magnetopause can be a driver of dynamic processes in the local space environment around this moon of Jupiter.”
The SwRI-developed Jovian Auroral Distributions Experiment (JADE) aboard Juno observed enhanced electron fluxes, including accelerated, magnetic field-aligned electrons. Reconnection as observed by Juno is thought to be related to the generation of Ganymede’s aurora.
“The accelerated electrons observed by JADE are similar to those observed by NASA’s Magnetospheric Multiscale (MSS) spacecraft during reconnection at the Earth’s magnetopause,” said Dr. Stephen Fuselier, a co-author of the paper. “That’s one of the exciting results from the Ganymede flyby: Despite the vast differences between Ganymede and Earth, we find commonality in the universal process of magnetic reconnection.”
During the Juno flyby, the SwRI-led Ultraviolet Spectrograph (UVS) observed Ganymede’s auroral emissions, which are expected to be produced by electrons accelerated via magnetic reconnection. SwRI has built two additional UVS instruments to operate in Jupiter orbit aboard ESA’s JUpiter ICy moons Explorer (JUICE) spacecraft and NASA’s Europa Clipper. The European Space Agency’s JUICE mission is scheduled to launch in April 2023 and arrive at Jupiter in 2031. NASA’s Europa Clipper is scheduled to launch in October 2024 and arrive at Jupiter in 2030.
“Nothing is simple — or small — when you have the biggest planet in the solar system as your neighbor,” said Thomas Greathouse, a Juno scientist from SwRI. “This was the first measurement of this complicated interaction at Ganymede. This gives us a very early tantalizing taste of the information we expect to learn from ESA’s JUICE mission.”
By their own admission, Anastasios “Andy” Tzanidakis and James Davenport are interested in unusual stars. The University of Washington astronomers were on the lookout for “stars behaving strangely” when an automated alert from the Gaia survey pointed them to Gaia17bpp. Survey data indicated that this star had gradually brightened over a 2 1/2-year period.
As Tzanidakis reported on Jan. 10 at the 241st meeting of the American Astronomical Society in Seattle, follow-up analyses indicated that Gaia17bpp itself wasn’t changing. Instead, the star is likely part of a rare type of binary system, and its apparent brightening was the end a years-long eclipse by an unusual stellar companion.
“We believe that this star is part of an exceptionally rare type of binary system, between a large, puffy older star — Gaia17bpp — and a small companion star that is surrounded by an expansive disk of dusty material,” said Tzanidakis, a UW doctoral student in astronomy. “Based on our analysis, these two stars orbit each other over an exceptionally long period of time — as much as 1,000 years. So, catching this bright star being eclipsed by its dusty companion is a once-in-a-lifetime opportunity.”
Since the Gaia spacecraft’s observations about the star only went back to 2014, Tzanidakis and Davenport, a UW research assistant professor of astronomy and associate director of the DiRAC Institute, had to do a little detective work to reach this conclusion. First, they stitched together Gaia’s observations of the star with observations by other missions stretching back to 2010 — including Pan-STARRS1, WISE/NEOWISE and the Zwicky Transient Facility.
Those observations, coupled with the Gaia data, showed that Gaia17bpp dimmed by about 4.5 magnitudes — or roughly 63 times. The star remained dim over the course of nearly seven years, from 2012 to 2019. The brightening that the Gaia survey had uncovered was the end of that seven-year dim.
No other stars near Gaia17bpp showed similar dimming behavior. Through the DASCH program, a digital catalog of more than a century’s worth of astro-photographic plates at Harvard, Tzanidakis and Davenport analyzed observations of the star stretching back to the 1950s.
“Over 66 years of observational history, we found no other signs of significant dimming in this star,” said Tzanidakis.
The two believe that Gaia17bpp is part of a rare type of binary star system, with a stellar companion that is — quite simply — dusty.
“Based on the data currently available, this star appears to have a slow-moving companion that is surrounded by a large disk of material,” said Tzanidakis. “If that material were in the solar system, it would extend from the sun to Earth’s orbit, or farther.”
During its eclipse, the unseen companion was blocking about 98% of Gaia17bpp’s light, according to Davenport.
A handful of other similar, “dusty” systems have been identified over the years, most notably Epsilon Aurigae, a star in the constellation Auriga that is eclipsed for two out of every 27 years by a relatively large, dim companion. The system that Tzanidakis and Davenport discovered is unique among these few dusty binaries in the length of the eclipse — at nearly seven years, it is by far the longest. Unlike the Epsilon Aurigae binary, Gaia17bpp and its companion are also so far apart that it would be centuries or more before an astute observer on Earth witnesses another such eclipse.
For Epsilon Aurigae and similar systems, the identity of the dusty companion is a matter of debate. Some preliminary data indicate that Gaia17bpp’s companion could be a small, massive white dwarf star. The source of its debris disk is also a mystery.
“This was a serendipitous discovery,” said Tzanidakis. “If we had been a few years off, we would’ve missed it. It also indicates that these types of binaries might be much more common. If so, we need to come up with theories about how this type of pairing even arose. It’s definitely an oddity, but it might be much more common than anyone has appreciated.”
Additional team members on this study are Eric Bellm, a UW research assistant professor of astronomy, and David Wang, a UW graduate student in astronomy.
An artistic rending of the star Gaia17bpp being partially eclipsed by the dust cloud surrounding a smaller companion star.
CREDIT
Anastasios Tzanidakis
The star Gaia17bpp, circled in red, as shown by the Pan-STARRS1 and DSS missions.
IMAGE: COLOUR SHOWS THE POLARIZED MICROWAVE EMISSION MEASURED BY QUIJOTE. THE PATTERN OF LINES SUPERPOSED SHOWS THE DIRECTION OF THE MAGNETIC FIELD LINES.view more
CREDIT: QUIJOTE COLLABORATION
The QUIJOTE experiment is sited at the Teide Observatory (Izaña, Tenerife) and comprises two telescopes, each of 2.25m diameter, which observe the sky in the microwave range (10-40 GHz). Led by the Instituto de Astrofísica de Canarias (IAC) this experiment started observing in 2012. Now, thanks to the data obtained with its multifrequency instrument MFI, which was working until 2018, a team of scientists has presented a set of six articles in the specialized journal Monthly Notices of the Royal Astronomical Society (MNRAS) that give the most accurate description until now of the polarization in the microwave emission processes in our galaxy.
“These maps give a detailed description in a new frequency range, from 10 to 20 GHz, complementary to those from space missions that have previously observed the sky at microwaves, such as Planck (ESA) and WMAP (NASA)”, comments José Alberto Rubiño, the scientist in charge of QUIJOTE, and Principal Investigator of the European project RADIOFOREGROUNDS. “We have characterized the synchrotron emission from our Galaxy with unprecedented accuracy. This radiation is the result of the emission by charged particles moving at velocities close to that of light within the Galactic magnetic field. These maps, the result of almost 9,000 hours of observation, are a unique tool for studying magnetism in the universe” he adds.
Polarized synchrotron radiation and the CMB
The CMB is the fossil radiation that originated during the first instants of the universe, and which we observe today at radio wavelength. This type of radiation is studied by scientists because “by studying the properties of its polarization we hope to find an indirect clue to the existence of gravitational waves after the Big Bang” comments Ricardo Génova-Santos (IAC), a member of the science team.
To measure this signal from the origin of the universe, the scientists need to eliminate the veil of emission associated with our own Galaxy. The new maps provided by QUIJOTE are a tool for performing this task. “One of the most interesting results we have found is that the polarized synchrotron emission from our Galaxy is much more variable than had been thought” comments Elena de la Hoz, a researcher at the Instituto de Física de Cantabria (IFCA). “The results we have obtained are a reference to help future experiments make reliable detections of the cosmological signal” she adds.
“The detection of this cosmological signal, a very specific pattern in the polarization of the microwave background associated with the presence of gravitational waves generated during the so-called inflationary epoch, opens a new window on fundamental physics” notes Rubiño, “which will allow us to explore scales of energy billions of times bigger than those which we can explore on the ground using particle accelerators. Studying it will help us to understand the energetic processes that took place at the birth of the universe”
Anomalous microwave emission
The new data from QUIJOTE are also a unique tool for studying the anomalous microwave emission (AME), a type of emission first detected 25 years ago, which is thought to be produced by the rotation of very small particles of dust in the interstellar medium, which tend to be aligned by the presence of the Galactic magnetic field.
“The polarization properties of these emissions must be characterized and understood in detail in order to decontaminate maps of the polarization of the CMB, leaving them free to study cosmology” comments Frédérick Poidevin, a researcher at the IAC. “Using the new results from QUIJOTE we have improved our understanding of the AME in numerous regions of our Galaxy, explains Denis Tramonte, a researcher at the Purple Mountain Observatory(PMO-CAS, China).
Further results
The maps from QUIJOTE have also permitted the study of the microwave emission from the centre of our Galaxy. Recently an excess of microwave emission has been detected from this region, whose origin is unknown, but whose origin could be connected to the decay processes of dark matter particles. With QUIJOTE we have confirmed the existence of this excess of radiation, and have found some evidence that it could be polarized” comments Federica Guidi, a researcher at the Institut d'Astrophysique de Paris (IAP, Francia).
Finally, the new maps from QUIJOTE have permitted the systematic study of over 700 sources of emission in radio and microwaves, of both Galactic and extragalactic origin. “For some 40 of these sources in which polarized emission has been detected, study of their properties gives agreement with the predictions of existing models in the literature” comments Diego Herranz, a researcher at IFCA
As well as these six articles, there are a further eight in preparation, soon to be sent for publication, which continue with the scientific exploitation of the QUIJOTE MFI maps.
QUIJOTE is the result of a scientific Collaboration between the IAC, IFCA, the Department of Engineering and Communications (Santander), the Jodrell Bank Centre for Astrophysics. of the University of Manchester, the Cavendish Laboratory (Cambridge) and the Idom company.
Map of polarized microwave emission in the northern hemisphere measured by QUIJOTE. The drapery pattern represents the direction of the Galactic magnetic field. The colour scale represents the intensity of the emission.
CREDIT
QUIJOTE Collaboration
QUIJOTE experiment at the Teide Observatory (Tenerife, Spain)
CHANGCHUN INSTITUTE OF OPTICS, FINE MECHANICS AND PHYSICS, CAS
IMAGE: (A) FAST’S OPTICAL GEOMETRY. (B) AUTOMATED OPTICAL INSPECTION AT FAST. (C) ILLUSTRATION OF SURFACE DEFECTS (DENT AND HOLE). (D) RESULTS OF DEFECT DETECTION.view more
CREDIT: BY JIANAN LI, SHENWANG JIANG, LIQIANG SONG, PEIRAN PENG, FENG MU, HUI LI, PENG JIANG, AND TINGFA XU
The Five-hundred-meter Aperture Spherical radio Telescope (FAST), also known as the “China Sky Eye”, is the world's largest single-dish radio telescope. Its reflector is a partial sphere of radius R=300 m. The planar partial spherical cap of the reflector has a diameter of 519.6 m, 1.7 times larger than that of the previously largest radio telescope. The large reflecting surface makes FAST the world's most sensitive radio telescope. It was used by astronomers to observe, for the first time, fast radio bursts in the Milky Way and to identify more than 500 new pulsars, four times the total number of pulsars identified by other telescopes worldwide. More interesting and exotic objects may yet be discovered using FAST.
However, each coin has two sides. A larger reflecting surface is more prone to external damage due to environmental factors. The FAST reflector comprises a total 4,450 spliced trilateral panels, made of aluminium with uniform perforations to reduce weight and wind impact. Falling objects (e.g., during the extreme events such as rockfalls, severe windstorms, and hailstorms) may cause severe dents and holes in the panels. Such defects adversely impact the study of small-wavelength radio waves, which demands a perfect dish surface. Any irregularity in the parabola scatters these small waves away from the focus, causing information loss.
The rapid detection of surface defects for timely repair is hence critical for maintaining the normal operation of FAST. This is traditionally done by direct visual inspection. Skilled inspectors climb up the reflector and visually examine the entire surface, searching for and replacing any panels showing dents and holes. However, this procedure has several limitations. Firstly, there is danger involved in accessing hard-to-reach places high above ground. Secondly, it is labour- and time-consuming to scrutinise all the thousands of panels. Thirdly, the procedure relies heavily on the inspectors' expertise and is prone to human-based errors and inconsistencies.
The remedy to the shortcomings of manual inspection at FAST is automated inspection. In a new paper published in Light: Advanced Manufacturing, a team of scientists led by Professor Jianan Li and Tingfa Xu from Beijing Institute of Technology make the first step towards automating the inspection of FAST by integrating deep-learning techniques with drone technology.
As a first step, the research team integrated deep-learning techniques with the use of drones to automatically detect defects on the reflector surface. Specifically, they began by manually controlling a drone equipped with a high-resolution RGB camera to fly over the surface along a predetermined route. During the flight, the camera captured and recorded videos of the surface condition. One benefit of the advanced flight stability of drones is that the recorded videos can capture much information on surface details. Moreover, thanks to the GPS device and the RTK module onboard the drone platform, every video frame can be tagged with the corresponding drone location with centimetre-level accuracy. The physical locations of the panels that appear in each frame can thus be determined.
To tackle the challenges of surface defects in drone imagery exhibiting large-scale variation and high inter-class similarity, they introduced a simple yet effective cross-fusion operation for deep detectors, which aggregates multi-level features in a point-wise selective manner to help detect defects of various scales and types. The cross-fusion method is lightweight and computationally efficient, particularly valuable features for onboard drone applications. Future work will implement the algorithm on embedded hardware platforms to process captured videos onboard the drone, to make the inspection system more autonomous and more robust.
A team of physicists devise a model that maps a star’s surprising orbit about a supermassive black hole – revealing new information about one of the cosmos’ most extreme environments.
IMAGE: THIS ILLUSTRATION SHOWS A GLOWING STREAM OF MATERIAL FROM A STAR AS IT IS BEING DEVOURED BY A SUPERMASSIVE BLACK HOLE IN A TIDAL DISRUPTION FLARE. WHEN A STAR PASSES WITHIN A CERTAIN DISTANCE OF A BLACK HOLE - CLOSE ENOUGH TO BE GRAVITATIONALLY DISRUPTED - THE STELLAR MATERIAL GETS STRETCHED AND COMPRESSED AS IT FALLS INTO THE BLACK HOLE.view more
CREDIT: NASAJPL-CALTECH
Hundreds of millions of light-years away in a distant galaxy, a star orbiting a supermassive black hole is being violently ripped apart under the black hole’s immense gravitational pull. As the star is shredded, its remnants are transformed into a stream of debris that rains back down onto the black hole to form a very hot, very bright disk of material swirling around the black hole, called an accretion disc. This phenomenon – where a star is destroyed by a supermassive black hole and fuels a luminous accretion flare – is known as a tidal disruption event (TDE), and it is predicted that TDEs occur roughly once every 10,000 to 100,000 years in a given galaxy.
With luminosities exceeding entire galaxies (i.e., billions of times brighter than our Sun) for brief periods of time (months to years), accretion events enable astrophysicists to study supermassive black holes (SMBHs) from cosmological distances, providing a window into the central regions of otherwise-quiescent - or dormant - galaxies. By probing these ``strong-gravity’’ events, where Einstein's general theory of relativity is critical for determining how matter behaves, TDEs yield information about one of the most extreme environments in the universe: the event horizon – the point of no return – of a black hole.
TDEs are usually “once-and-done” because the extreme gravitational field of the SMBH destroys the star, meaning that the SMBH fades back into darkness following the accretion flare. In some instances, however, the high-density core of the star can survive the gravitational interaction with the SMBH, allowing it to orbit the black hole more than once. Researchers call this a repeating partial TDE.
A team of physicists, including lead author Thomas Wevers, Fellow of the European Southern Observatory, and co-authors Eric Coughlin, assistant professor of physics at Syracuse University, and Dheeraj R. “DJ” Pasham, research scientist at MIT’s Kavli Institute for Astrophysics and Space Research, have proposed a model for a repeating partial TDE. Their findings, published in Astrophysical Journal Letters, describe the capture of the star by a SMBH, the stripping of the material each time the star comes close to the black hole, and the delay between when the material is stripped and when it feeds the black hole again. The team’s work is the first to develop and use a detailed model of a repeating partial TDE to explain the observations, make predictions about the orbital properties of a star in a distant galaxy, and understand the partial tidal disruption process.
The team is studying a TDE known as AT2018fyk (AT stands for ``Astrophysical Transient’’). The star was captured by a SMBH through an exchange process known as “Hills capture,” where the star was originally part of a binary system (two stars that orbit one another under their mutual gravitational attraction) that was ripped apart by the gravitational field of the black hole. The other (non-captured) star was ejected from the center of the galaxy at speeds comparable to ~ 1000 km/s, which is known as a hypervelocity star.
Once bound to the SMBH, the star powering the emission from AT2018fyk has been repeatedly stripped of its outer envelope each time it passes through its point of closest approach with the black hole. The stripped outer layers of the star form the bright accretion disk, which researchers can study using X-Ray and Ultraviolet /Optical telescopes that observe light from distant galaxies.
According to Wevers, having the opportunity to study a partial TDE gives unprecedented insight into the existence of supermassive black holes and the orbital dynamics of stars in the centers of galaxies.
“Until now, the assumption has been that when we see the aftermath of a close encounter between a star and a supermassive black hole, the outcome will be fatal for the star, that is, the star is completely destroyed,” he says. “But contrary to all other TDEs we know of, when we pointed our telescopes to the same location again several years later, we found that it had re-brightened again. This led us to propose that rather than being fatal, part of the star survived the initial encounter and returned to the same location to be stripped of material once more, explaining the re-brightening phase.”
First detected in 2018, AT2018fyk was initially perceived as an ordinary TDE. For approximately 600 days the source stayed bright in the X-ray, but then abruptly went dark and was undetectable - a result of the stellar remnant core returning to a black hole, explains MIT physicist Dheeraj R. Pasham.
“When the core returns to the black hole it essentially steals all the gas away from the black hole via gravity and as a result there is no matter to accrete and hence the system goes dark,” Pasham says.
It wasn’t immediately clear what caused the precipitous decline in the luminosity of AT2018fyk, because TDEs normally decay smoothly and gradually – not abruptly – in their emission. But around 600 days after the drop, the source was again found to be X-ray bright. This led the researchers to propose that the star survived its close encounter with the SMBH the first time and was in orbit about the black hole.
Using detailed modeling, the team’s findings suggest that the orbital period of the star about the black hole is roughly 1,200 days, and it takes approximately 600 days for the material that is shed from the star to return to the black hole and start accreting. Their model also constrained the size of the captured star, which they believe was about the size of the sun. As for the original binary, the team believes the two stars were extremely close to one another before being ripped apart by the black hole, likely orbiting each other every few days.
So how could a star survive its brush with death? It all comes down to a matter of proximity and trajectory. If the star collided head-on with the black hole and passed the event horizon – the threshold where the speed needed to escape the black hole surpasses the speed of light – the star would be consumed by the black hole. If the star passed very close to the black hole and crossed the so-called "tidal radius" – where the tidal force of the hole is stronger than the gravitational force that keeps the star together – it would be destroyed. In the model they have proposed, the star's orbit reaches a point of closest approach that is just outside of the tidal radius, but doesn't cross it completely: some of the material at the stellar surface is stripped by the black hole, but the material at its center remains intact.
How, or if, the process of the star orbiting the SMBH can occur over many repeated passages is a theoretical question that the team plans to investigate with future simulations. Syracuse physicist Eric Coughlin explains that they estimate between 1 to 10% of the mass of the star is lost each time it passes the black hole, with the large range due to uncertainty in modeling the emission from the TDE.
“If the mass loss is only at the 1% level, then we expect the star to survive for many more encounters, whereas if it is closer to 10%, the star may have already been destroyed,” notes Coughlin.
The team will keep their eyes to the sky in the coming years to test their predictions. Based on their model, they forecast that the source will abruptly disappear around August 2023 and brighten again when the freshly stripped material accretes onto the black hole in 2025.
The team says their study offers a new way forward for tracking and monitoring follow-up sources that have been detected in the past. The work also suggests a new paradigm for the origin of repeating flares from the centers of external galaxies.
“In the future, it is likely that more systems will be checked for late-time flares, especially now that this project puts forth a theoretical picture of the capture of the star through a dynamical exchange process and the ensuing repeated partial tidal disruption,” says Coughlin. “We’re hopeful this model can be used to infer the properties of distant supermassive black holes and gain an understanding of their “demographics,” being the number of black holes within a given mass range, which is otherwise difficult to achieve directly.”
The team says the model also makes several testable predictions about the tidal disruption process, and with more observations of systems like AT2018fyk, it should give insight into the physics of partial tidal disruption events and the extreme environments around supermassive black holes.
“This study outlines methodology to potentially predict the next snack times of supermassive black holes in external galaxies,” says Pasham. “If you think about it, it is pretty remarkable that we on Earth can align our telescopes to black holes millions of light years away to understand how they feed and grow.”
This illustration depicts a star (in the foreground) experiencing spaghettification as it’s sucked in by a supermassive black hole (in the background) during a ‘tidal disruption event’.
CREDIT
ESOM Kornmesser
Additional co-authors include: M. Guolo, Department of Physics and Astronomy, Johns Hopkins University; Y. Sun, University of Arizona; S. Wen, Department of Astrophysics/IMAPP, Radboud University ; P.G. Jonker, Department of Astrophysics/IMAPP, Radboud University and SRON, Netherlands Institute for Space Research ; A. Zabludoff, University of Arizona; A. Malyali, R. Arcodia, Z. Liu, A. Merloni, A. Rau and I. Grotova, Max-Planck-Institut fu ̈r extraterrestrische Physik , Germany; P. Short, Institute for Astronomy, University of Edinburgh; and Z. Cao, Department of Astrophysics/IMAPP, Radboud University
Video: https://youtu.be/_TRtPDbaQ2k Animation describing a partial tidal disruption event – where a black hole repeatedly destroys a star.
JOURNAL
The Astrophysical Journal Letters
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
The American Astronomical Society, find out more The Institute of Physics, find out more THE FOLLOWING ARTICLE ISOPEN ACCESS Live to Die Another Day: The Rebrightening of AT 2018fyk as a Repeating Partial Tidal Disruption Event
DONUTIZATION
Hubble finds hungry black hole twisting captured star into donut shape
IMAGE: THIS SEQUENCE OF ARTIST'S ILLUSTRATIONS SHOWS HOW A BLACK HOLE CAN DEVOUR A BYPASSING STAR. 1. A NORMAL STAR PASSES NEAR A SUPERMASSIVE BLACK HOLE IN THE CENTER OF A GALAXY. 2. THE STAR'S OUTER GASSES ARE PULLED INTO THE BLACK HOLE'S GRAVITATIONAL FIELD. 3. THE STAR IS SHREDDED AS TIDAL FORCES PULL IT APART. 4. THE STELLAR REMNANTS ARE PULLED INTO A DONUT-SHAPED RING AROUND THE BLACK HOLE, AND WILL EVENTUALLY FALL INTO THE BLACK HOLE, UNLEASHING A TREMENDOUS AMOUNT OF LIGHT AND HIGH-ENERGY RADIATION.view more
CREDIT: NASA, ESA, LEAH HUSTAK (STSCI)
Black holes are gatherers, not hunters. They lie in wait until a hapless star wanders by. When the star gets close enough, the black hole's gravitational grasp violently rips it apart and sloppily devours its gasses while belching out intense radiation.
Astronomers using NASA's Hubble Space Telescope have recorded a star's final moments in detail as it gets gobbled up by a black hole.
These are termed "tidal disruption events." But the wording belies the complex, raw violence of a black hole encounter. There is a balance between the black hole's gravity pulling in star stuff, and radiation blowing material out. In other words, black holes are messy eaters. Astronomers are using Hubble to find out the details of what happens when a wayward star plunges into the gravitational abyss.
Hubble can't photograph the AT2022dsb tidal event's mayhem up close, since the munched-up star is nearly 300 million light-years away at the core of the galaxy ESO 583-G004. But astronomers used Hubble's powerful ultraviolet sensitivity to study the light from the shredded star, which include hydrogen, carbon, and more. The spectroscopy provides forensic clues to the black hole homicide.
About 100 tidal disruption events around black holes have been detected by astronomers using various telescopes. NASA recently reported that several of its high-energy space observatories spotted another black hole tidal disruption event on March 1, 2021, and it happened in another galaxy. Unlike Hubble observations, data was collected in X-ray light from an extremely hot corona around the black hole that formed after the star was already torn apart.
"However, there are still very few tidal events that are observed in ultraviolet light given the observing time. This is really unfortunate because there's a lot of information that you can get from the ultraviolet spectra," said Emily Engelthaler of the Center for Astrophysics | Harvard & Smithsonian (CfA) in Cambridge, Massachusetts. "We're excited because we can get these details about what the debris is doing. The tidal event can tell us a lot about a black hole." Changes in the doomed star's condition are taking place on the order of days or months.
For any given galaxy with a quiescent supermassive black hole at the center, it's estimated that the stellar shredding happens only a few times in every 100,000 years.
This AT2022dsb stellar snacking event was first caught on March 1, 2022 by the All-Sky Automated Survey for Supernovae (ASAS-SN or "Assassin"), a network of ground-based telescopes that surveys the extragalactic sky roughly once a week for violent, variable, and transient events that are shaping our universe. This energetic collision was close enough to Earth and bright enough for the Hubble astronomers to do ultraviolet spectroscopy over a longer than normal period of time.
"Typically, these events are hard to observe. You get maybe a few observations at the beginning of the disruption when it's really bright. Our program is different in that it is designed to look at a few tidal events over a year to see what happens," said Peter Maksym of the CfA. "We saw this early enough that we could observe it at these very intense black hole accretion stages. We saw the accretion rate drop as it turned to a trickle over time."
The Hubble spectroscopic data are interpreted as coming from a very bright, hot, donut-shaped area of gas that was once the star. This area, known as a torus, is the size of the solar system and is swirling around a black hole in the middle.
"We're looking somewhere on the edge of that donut. We're seeing a stellar wind from the black hole sweeping over the surface that's being projected towards us at speeds of 20 million miles per hour (three percent the speed of light)," said Maksym. "We really are still getting our heads around the event. You shred the star and then it's got this material that's making its way into the black hole. And so you've got models where you think you know what is going on, and then you've got what you actually see. This is an exciting place for scientists to be: right at the interface of the known and the unknown."
The Hubble Space Telescope is a project of international cooperation between NASA and ESA. NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble and Webb science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.
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