ST/ Astronomers detect ‘nearby’ black hole devouring a star
Space biweekly vol.76, 20th April — 5th May
TL;DR
- MIT astronomers have discovered a new ‘tidal disruption event,’ in which the center of a galaxy lights up as its supermassive black hole rips apart a passing star. The outburst is the closest tidal disruption event observed to date, and one of the first to be identified at infrared wavelengths.
- A new study looked at a known binary star (two stars orbiting around a mutual center of gravity), analyzing starlight obtained from a range of ground- and space-based telescopes. The researchers found that the stars, located in a neighboring dwarf galaxy called the Small Magellanic Cloud, are in partial contact and swapping material with each other, with one star currently ‘feeding’ off the other. They orbit each other every three days and are the most massive touching stars (known as contact binaries) yet observed.
- A team of Japanese astronomers used simultaneous ground-based and space-based observations to capture a more complete picture of a superflare on a star. The observed flare started with a very massive, high-velocity prominence eruption. These results give us a better idea of how superflares and stellar prominence eruptions occur.
- Astronomers have observed, in one image, the shadow of the black hole at the center of the galaxy Messier 87 (M87) and the powerful jet expelled from it. Thanks to this new image, astronomers can better understand how black holes can launch such energetic jets.
- Scientists have unlocked one of the biggest mysteries of quasars — the brightest, most powerful objects in the Universe — by discovering that they are ignited by galaxies colliding.
- In new 3D computer simulations, astrophysicists modeled black holes of varying masses and then hurled stars (about the size of our sun) past them to see what might happen. If they exist, intermediate-mass black holes likely devour wayward stars like a messy toddler — taking a few bites and then flinging the remains across the galaxy.
- Astrophysicists have provided the most direct evidence yet that Dark Matter does not constitute ultramassive particles as is commonly thought but instead comprises particles so light that they travel through space like waves. Their work resolves an outstanding problem in astrophysics first raised two decades ago: why do models that adopt ultramassive Dark Matter particles fail to correctly predict the observed positions and the brightness of multiple images of the same galaxy created by gravitational lensing?
- A new study has uncovered intriguing insights into the liquid core at the centre of Mars, furthering understanding of the planet’s formation and evolution.
- A research team has confirmed evidence of a previously unknown planet outside of our solar system, and they used machine learning tools to detect it. A recent study by the team showed that machine learning can correctly determine if an exoplanet is present by looking in protoplanetary disks, the gas around newly formed stars. The newly published findings represent a first step toward using machine learning to identify previously overlooked exoplanets.
- A study using data from telescopes on Earth and in the sky resolves a problem plaguing astronomers working in the infrared and could help make better observations of the composition of the universe with the James Webb Space Telescope and other instruments.
- And more!
Space industry in numbers
The global smart space market size is projected to grow from USD 9.4 billion in 2020 to USD 15.3 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 10.2% during the forecast period. The increasing venture capital funding and growing investments in smart space technology to drive market growth.
Analysts at Morgan Stanley and Goldman Sachs have predicted that economic activity in space will become a multi-trillion-dollar market in the coming decades. Morgan Stanley’s Space Team estimates that the roughly USD 350 billion global space industry could surge to over USD 1 trillion by 2040.
Space industry news
- Court approves plans for Virgin Orbit bankruptcy sale
- Environmental groups sue FAA over Starship launch license
- Lawmakers raise concerns about new plan to procure national security launch service
- ESA troubleshooting JUICE radar antenna
- SpaceX Falcon Heavy launches first ViaSat-3 satellite
- Musk predicts next Starship launch in a “couple months”
- SpaceX launches second pair of O3b mPower satellites
- Orienspace of China targets first launch in second half of the year
- Air Force navigation satellite experiment applying lessons from GPS
- Astra, Exotrail win satellite propulsion orders
- Spaceport Cornwall expands facilities following Virgin Orbit failure
- China to establish organization to coordinate international moon base
- Nelson expects SpaceX to be ready for next Starship launch within months
- Russia commits to ISS extension to 2028
- Chinese state-owned academy makes rocket engines available to commercial space firms
- Spain’s Satlantis expands into thermal imagery with UK investment
- Light Steering Technologies claims $1.25 million Air Force contract
- Raytheon rethinks strategy to compete in military satellite market
- Albedo wins Air Force contract to supply thermal imagery at night
Latest research
A Luminous Dust-obscured Tidal Disruption Event Candidate in a Star-forming Galaxy at 42 Mpc
by Christos Panagiotou, Kishalay De, Megan Masterson, Erin Kara, Michael Calzadilla, Anna-Christina Eilers, Danielle Frostig, Viraj Karambelkar, Mansi Kasliwal, Nathan Lourie, Aaron M. Meisner, Robert A. Simcoe, Robert Stein, Jeffry Zolkower in The Astrophysical Journal Letters
Once every 10,000 years or so, the center of a galaxy lights up as its supermassive black hole rips apart a passing star. This “tidal disruption event” happens in a literal flash, as the central black hole pulls in stellar material and blasts out huge amounts of radiation in the process.
Astronomers know of around 100 tidal disruption events (TDE) in distant galaxies, based on the burst of light that arrives at telescopes on Earth and in space. Most of this light comes from X-rays and optical radiation.
MIT astronomers, tuning past the conventional X-ray and UV/optical bands, have discovered a new tidal disruption event, shining brightly in infrared. It is one of the first times scientists have directly identified a TDE at infrared wavelengths. What’s more, the new outburst happens to be the closest tidal disruption event observed to date: The flare was found in NGC 7392, a galaxy that is about 137 million light-years from Earth, which corresponds to a region in our cosmic backyard that is one-fourth the size of the next-closest TDE.
This new flare, labeled WTP14adbjsh, did not stand out in standard X-ray and optical data. The scientists suspect that these traditional surveys missed the nearby TDE, not because it did not emit X-rays and UV light, but because that light was obscured by an enormous amount of dust that absorbed the radiation and gave off heat in the form of infrared energy.
The researchers determined that WTP14adbjsh occurred in a young, star-forming galaxy, in contrast to the majority of TDEs that have been found in quieter galaxies. Scientists expected that star-forming galaxies should host TDEs, as the stars they churn out would provide plenty of fuel for a galaxy’s central black hole to devour. But observations of TDEs in star-forming galaxies were rare until now.
The new study suggests that conventional X-ray and optical surveys may have missed TDEs in star-forming galaxies because these galaxies naturally produce more dust that could obscure any light coming from their core. Searching in the infrared band could reveal many more, previously hidden TDEs in active, star-forming galaxies. Panagiotou’s MIT co-authors are Kishalay De, Megan Masterson, Erin Kara, Michael Calzadilla, Anna-Christina Eilers, Danielle Frostig, Nathan Lourie, and Rob Simcoe, along with Viraj Karambelkar, Mansi Kasliwal, Robert Stein, and Jeffry Zolkower of Caltech, and Aaron Meisner at the National Science Foundation’s National Optical-Infrared Astronomy Research Laboratory.
“Finding this nearby TDE means that, statistically, there must be a large population of these events that traditional methods were blind to,” says Christos Panagiotou, a postdoc in MIT’s Kavli Institute for Astrophysics and Space Research. “So, we should try to find these in infrared if we want a complete picture of black holes and their host galaxies.”
Panagiotou did not intend to search for tidal disruption events. He and his colleagues were looking for signs of general transient sources in observational data, using a search tool developed by De. The team used De’s method to look for potential transient events in archival data taken by NASA’s NEOWISE mission, a space telescope that has made regular scans of the entire sky since 2010, at infrared wavelengths. The team discovered a bright flash that appeared in the sky near the end of 2014.
“We could see there was nothing at first,” Panagiotou recalls. “Then suddenly, in late 2014, the source got brighter and by 2015 reached a high luminosity, then started going back to its previous quiescence.”
They traced the flash to a galaxy 42 megarparsecs from Earth. The question then was, what set it off? To answer this, the team considered the brightness and timing of the flash, comparing the actual observations with models of various astrophysical processes that could produce a similar flash.
“For instance, supernovae are sources that explode and brighten suddenly, then come back down, on similar timescales to tidal disruption events,” Panagiotou notes. “But supernovae are not as luminous and energetic as what we observed.”
Working through different possibilities of what the burst could be, the scientists were finally able to exclude all but one: The flash was most likely a TDE, and the closest one observed so far.
“It’s a very clean light curve and really follows what we expect the temporal evolution of a TDE should be,” Panagiotou says.
From there, the researchers took a closer look at the galaxy where the TDE arose. They gathered data from multiple ground- and space-based telescopes which happened to observe the part of the sky where the galaxy resides, across various wavelengths, including infrared, optical, and X-ray bands. With this accumulated data, the team estimated that the supermassive black hole at the center of the galaxy was about 30 million times as massive as the sun.
“This is almost 10 times larger than the black hole we have at our galactic center, so it’s quite massive, though black holes can get up to 10 billion solar masses,” Panagiotou says.
The team also found that the galaxy itself is actively producing new stars. Star-forming galaxies are a class of “blue” galaxies, in contrast to quieter “red” galaxies that have stopped producing new stars. Star-forming blue galaxies are the most common type of galaxy in the universe.
“Green” galaxies lie somewhere between red and blue, in that, every so often they produce a few stars. Green is the least common galaxy type, but curiously, most TDEs detected to date have been traced to these rarer galaxies. Scientists had struggled to explain these detections, since theory predicts that blue star-forming galaxies should exhibit TDEs, as they would present more stars for black holes to disrupt. But star-forming galaxies also produce a lot of dust from the interactions between and among stars near a galaxy’s core. This dust is detectable at infrared wavelengths, but it can obscure any X-ray or UV radiation that would otherwise be picked up by optical telescopes. This could explain why astronomers have not detected TDEs in star-forming galaxies using conventional optical methods.
“The fact that optical and X-ray surveys missed this luminous TDE in our own backyard is very illuminating, and demonstrates that these surveys are only giving us a partial census of the total population of TDEs,” says Suvi Gezari, associate astronomer and chair of the Science Staff at the Space Telescope Science Institute in Maryland, who was not involved in the study. “Using infrared surveys to catch the dust echo of obscured TDEs…has already shown us that there is a population of TDEs in dusty, star-forming galaxies that we have been missing.”
A low-metallicity massive contact binary undergoing slow Case A mass transfer: A detailed spectroscopic and orbital analysis of SSN 7 in NGC 346 in the SMC
by M. J. Rickard, D. Pauli in Astronomy & Astrophysics
Two massive touching stars in a neighbouring galaxy are on course to become black holes that will eventually crash together, generating waves in the fabric of space-time, according to a new study by researchers at UCL (University College London) and the University of Potsdam.
The study looked at a known binary star (two stars orbiting around a mutual centre of gravity), analysing starlight obtained from a range of ground- and space-based telescopes. The researchers found that the stars, located in a neighbouring dwarf galaxy called the Small Magellanic Cloud, are in partial contact and swapping material with each other, with one star currently “feeding” off the other. They orbit each other every three days and are the most massive touching stars (known as contact binaries) yet observed.
Comparing the results of their observations with theoretical models of binary stars’ evolution, they found that, in the best-fit model, the star that is currently being fed on will become a black hole and will feed on its companion star. The surviving star will become a black hole shortly after. These black holes will form in only a couple of million years, but will then orbit each other for billions of years before colliding with such force that they will generate gravitational waves — ripples in the fabric of space-time — that could theoretically be detected with instruments on Earth.
PhD student Matthew Rickard (UCL Physics & Astronomy), lead author of the study, said: “Thanks to gravitational wave detectors Virgo and LIGO, dozens of black hole mergers have been detected in the last few years. But so far we have yet to observe stars that are predicted to collapse into black holes of this size and merge in a time scale shorter than or even broadly comparable to the age of the universe.
“Our best-fit model suggests these stars will merge as black holes in 18 billion years. Finding stars on this evolutionary pathway so close to our Milky Way galaxy presents us with an excellent opportunity learn even more about how these black hole binaries form.”
Co-author Daniel Pauli, a PhD student at the University of Potsdam, said: “This binary star is the most massive contact binary observed so far. The smaller, brighter, hotter star, 32 times the mass of the Sun, is currently losing mass to its bigger companion, which has 55 times our Sun’s mass.”
The black holes that astronomers see merge today formed billions of years ago, when the universe had lower levels of iron and other heavier elements. The proportion of these heavy elements has increased as the universe has aged and this makes black hole mergers less likely. This is because stars with a higher proportion of heavier elements have stronger winds and they blow themselves apart sooner. The well-studied Small Magellanic Cloud, about 210,000 light years from Earth, has by a quirk of nature about a seventh of the iron and other heavy metal abundances of our own Milky Way galaxy. In this respect it mimics conditions in the universe’s distant past. But unlike older, more distant galaxies, it is close enough for astronomers to measure the properties of individual and binary stars.
In their study, the researchers measured different bands of light coming from the binary star (spectroscopic analysis), using data obtained over multiple periods of time by instruments on NASA’s Hubble Space Telescope (HST) and the Multi Unit Spectroscopic Explorer (MUSE) on ESO’s Very Large Telescope in Chile, among other telescopes, in wavelengths ranging from ultraviolet to optical to near infrared. With this data, the team were able to calculate the radial velocity of the stars — that is, the movement they made towards or away from us — as well as their masses, brightness, temperature and orbits. They then matched these parameters with the best-fit evolutionary model.
Their spectroscopic analysis indicated that much of the outer envelope of the smaller star had been stripped away by its larger companion. They also observed the radius of both stars exceeded their Roche lobe — that is, the region around a star where material is gravitationally bound to that star — confirming that some of the smaller star’s material is overflowing and transferring to the companion star.
Talking through the future evolution of the stars, Rickard explained: “The smaller star will become a black hole first, in as little as 700,000 years, either through a spectacular explosion called a supernova or it may be so massive as to collapse into a black hole with no outward explosion. “They will be uneasy neighbours for around three million years before the first black hole starts accreting mass from its companion, taking revenge on its companion.”
Pauli, who conducted the modelling work, added: “After only 200,000 years, an instant in astronomical terms, the companion star will collapse into a black hole as well. These two massive stars will continue to orbit each other, going round and round every few days for billions of years.
“Slowly they will lose this orbital energy through the emission of gravitational waves until they orbit each other every few seconds, finally merging together in 18 billion years with a huge release of energy through gravitational waves.”
Detection of a High-velocity Prominence Eruption Leading to a CME Associated with a Superflare on the RS CVn-type Star V1355 Orionis
by Shun Inoue, Hiroyuki Maehara, Yuta Notsu, Kosuke Namekata, Satoshi Honda, Keiichi Namizaki, Daisaku Nogami, Kazunari Shibata in The Astrophysical Journal
A team of Japanese astronomers used simultaneous ground-based and space-based observations to capture a more complete picture of a superflare on a star. The observed flare started with a very massive, high-velocity prominence eruption. These results give us a better idea of how superflares and stellar prominence eruptions occur.
Some stars have been seen releasing superflares over 10 times larger than the largest solar flare ever seen on the Sun. The hot ionized gas released by solar flares can influence the environment around the Earth, referred to as space weather. More powerful superflares must have an even greater impact on the evolution of any planets forming around the star, or the evolution of any life forming on those planets. But the details of how superflares and prominence eruptions on stars occur have been unclear.
A team led by Shun Inoue at Kyoto University used the 3.8-m Seimei Telescope in Japan and the Transiting Exoplanet Survey Satellite (TESS) to monitor the binary star system V1355 Orionis which is known to frequently release large-scale superflares. V1355 Orionis is located 400 light years away in the constellation Orion.
The team succeeded in capturing a superflare with continuous, high temporal resolution observations. Data analysis shows that the superflare originated with a phenomenon known as a prominence eruption. Calculating the velocity of the eruption requires making some assumptions about aspects that aren’t directly observably, but even the most conservative estimates far exceed the escape velocity of the star (347 km/s), indicating that the prominence eruption was capable of breaking free of the star’s gravity and developing into Coronal Mass Ejections (CMEs). The prominence eruption was also one of the most massive ever observed, carrying trillions of tons of material.
A ring-like accretion structure in M87 connecting its black hole and jet
by Ru-Sen Lu, Keiichi Asada, Thomas P. Krichbaum, Jongho Park, Fumie Tazaki, et al in Nature
For the first time, astronomers have observed, in the same image, the shadow of the black hole at the centre of the galaxy Messier 87 (M87) and the powerful jet expelled from it. The observations were done in 2018 with telescopes from the Global Millimetre VLBI Array (GMVA), the Atacama Large Millimeter/submillimeter Array (ALMA), of which ESO is a partner, and the Greenland Telescope (GLT). Thanks to this new image, astronomers can better understand how black holes can launch such energetic jets.
Most galaxies harbour a supermassive black hole at their centre. While black holes are known for engulfing matter in their immediate vicinity, they can also launch powerful jets of matter that extend beyond the galaxies that they live in. Understanding how black holes create such enormous jets has been a long standing problem in astronomy.
“We know that jets are ejected from the region surrounding black holes,” says Ru-Sen Lu from the Shanghai Astronomical Observatory in China, “but we still do not fully understand how this actually happens. To study this directly we need to observe the origin of the jet as close as possible to the black hole.”
The new image published today shows precisely this for the first time: how the base of a jet connects with the matter swirling around a supermassive black hole. The target is the galaxy M87, located 55 million light-years away in our cosmic neighbourhood, and home to a black hole 6.5 billion times more massive than the Sun. Previous observations had managed to separately image the region close to the black hole and the jet, but this is the first time both features have been observed together. “This new image completes the picture by showing the region around the black hole and the jet at the same time,” adds Jae-Young Kim from the Kyungpook National University in South Korea and the Max Planck Institute for Radio Astronomy in Germany.
The image was obtained with the GMVA, ALMA and the GLT, forming a network of radio-telescopes around the globe working together as a virtual Earth-sized telescope. Such a large network can discern very small details in the region around M87’s black hole.
The new image shows the jet emerging near the black hole, as well as what scientists call the shadow of the black hole. As matter orbits the black hole, it heats up and emits light. The black hole bends and captures some of this light, creating a ring-like structure around the black hole as seen from Earth. The darkness at the centre of the ring is the black hole shadow, which was first imaged by the Event Horizon Telescope (EHT) in 2017. Both this new image and the EHT one combine data taken with several radio-telescopes worldwide, but the image released today shows radio light emitted at a longer wavelength than the EHT one: 3.5 mm instead of 1.3 mm. “At this wavelength, we can see how the jet emerges from the ring of emission around the central supermassive black hole,” says Thomas Krichbaum of the Max Planck Institute for Radio Astronomy.
The size of the ring observed by the GMVA network is roughly 50% larger in comparison to the Event Horizon Telescope image. “To understand the physical origin of the bigger and thicker ring, we had to use computer simulations to test different scenarios,” explains Keiichi Asada from the Academia Sinica in Taiwan. The results suggest the new image reveals more of the material that is falling towards the black hole than what could be observed with the EHT.
These new observations of M87’s black hole were conducted in 2018 with the GMVA, which consists of 14 radio-telescopes in Europe and North America [1]. In addition, two other facilities were linked to the GMVA: the Greenland Telescope and ALMA, of which ESO is a partner. ALMA consists of 66 antennas in the Chilean Atacama desert, and it played a key role in these observations. The data collected by all these telescopes worldwide are combined using a technique called interferometry, which synchronises the signals taken by each individual facility. But to properly capture the actual shape of an astronomical object it’s important that the telescopes are spread all over the Earth. The GMVA telescopes are mostly aligned East-to-West, so the addition of ALMA in the Southern hemisphere proved essential to capture this image of the jet and shadow of M87’s black hole. “Thanks to ALMA’s location and sensitivity, we could reveal the black hole shadow and see deeper into the emission of the jet at the same time,” explains Lu.
Future observations with this network of telescopes will continue to unravel how supermassive black holes can launch powerful jets. “We plan to observe the region around the black hole at the centre of M87 at different radio wavelengths to further study the emission of the jet,” says Eduardo Ros from the Max Planck Institute for Radio Astronomy. Such simultaneous observations would allow the team to disentangle the complicated processes that happen near the supermassive black hole. “The coming years will be exciting, as we will be able to learn more about what happens near one of the most mysterious regions in the Universe,” concludes Ros.
Galaxy interactions are the dominant trigger for local type 2 quasars
by J C S Pierce, C Tadhunter, C Ramos Almeida, P Bessiere, J V Heaton, S L Ellison, G Speranza, Y Gordon, C O’Dea, L Grimmett, L Makrygianni in Monthly Notices of the Royal Astronomical Society
Scientists have unlocked one of the biggest mysteries of quasars — the brightest, most powerful objects in the Universe — by discovering that they are ignited by galaxies colliding.
First discovered 60 years ago, quasars can shine as brightly as a trillion stars packed into a volume the size of our Solar System. In the decades since they were first observed, it has remained a mystery what could trigger such powerful activity. New work led by scientists at the Universities of Sheffield and Hertfordshire has now revealed that it is a consequence of galaxies crashing together. The collisions were discovered when researchers, using deep imaging observations from the Isaac Newton Telescope in La Palma, observed the presence of distorted structures in the outer regions of the galaxies that are home to quasars.
Most galaxies have supermassive black holes at their centres. They also contain substantial amounts of gas — but most of the time this gas is orbiting at large distances from the galaxy centres, out of reach of the black holes. Collisions between galaxies drive the gas towards the black hole at the galaxy centre; just before the gas is consumed by the black hole, it releases extraordinary amounts of energy in the form of radiation, resulting in the characteristic quasar brilliance.
The ignition of a quasar can have dramatic consequences for entire galaxies — it can drive the rest of the gas out of the galaxy, which prevents it from forming new stars for billions of years into the future. This is the first time that a sample of quasars of this size has been imaged with this level of sensitivity. By comparing observations of 48 quasars and their host galaxies with images of over 100 non-quasar galaxies, researchers concluded that galaxies hosting quasars are approximately three times as likely to be interacting or colliding with other galaxies. The study has provided a significant step forward in our understanding of how these powerful objects are triggered and fuelled.
Professor Clive Tadhunter, from the University of Sheffield’s Department of Physics and Astronomy, said: “Quasars are one of the most extreme phenomena in the Universe, and what we see is likely to represent the future of our own Milky Way galaxy when it collides with the Andromeda galaxy in about five billion years.
“It’s exciting to observe these events and finally understand why they occur — but thankfully Earth won’t be anywhere near one of these apocalyptic episodes for quite some time.”
Quasars are important to astrophysicists because, due to their brightness, they stand out at large distances and therefore act as beacons to the earliest epochs in the history of the Universe. Dr Jonny Pierce, Post-Doctoral Research Fellow at the University of Hertfordshire, explains:
“It’s an area that scientists around the world are keen to learn more about — one of the main scientific motivations for NASA’s James Webb Space Telescope was to study the earliest galaxies in the Universe, and Webb is capable of detecting light from even the most distant quasars, emitted nearly 13 billion years ago. Quasars play a key role in our understanding of the history of the Universe, and possibly also the future of the Milky Way.”
Tidal Disruption of Main-Sequence Stars by Intermediate-Mass Black Holes
by Fulya Kıroğlu, James C. Lombardi Jr., Kyle Kremer, Giacomo Fragione, Shane Fogarty, Frederic A. Rasio in arXiv
If they exist, intermediate-mass black holes likely devour wayward stars like a messy toddler — taking a few bites and then flinging the remains across the galaxy — a new Northwestern University-led study has found.
In new 3D computer simulations, astrophysicists modeled black holes of varying masses and then hurled stars (about the size of our sun) past them to see what might happen. When a star approaches an intermediate-mass black hole, it initially gets caught in the black hole’s orbit, the researchers discovered. After that, the black hole begins its lengthy and violent meal. Every time the star makes a lap, the black hole takes a bite — further cannibalizing the star with each passage. Eventually, nothing is left but the star’s misshapen and incredibly dense core.
At that point, the black hole ejects the remains. The star’s remnant flies to safety across the galaxy. Not only do these new simulations hint at the unknown behaviors of intermediate-mass black holes, they also provide astronomers with new clues to help finally pinpoint these hidden giants within our night sky.
“We obviously cannot observe black holes directly because they don’t emit light,” said Northwestern’s Fulya Kıroğlu, who led the study. “So, instead, we have to look at the interactions between black holes and their environments. We found that stars undergo multiple passages before being ejected. After each passage, they lose more mass, causing a flair of light as its ripped apart. Each flare is brighter than the last, creating a signature that might help astronomers find them.”
Kıroğlu is an astrophysics graduate student at Northwestern’s Weinberg College of Arts and Sciences and member of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). She is advised by paper co-author Frederic Rasio, the Joseph Cummings Professor of Physics and Astronomy at Weinberg and member of CIERA.
While astrophysicists have proven the existence of lower- and higher-mass block holes, intermediate-mass black holes have remained elusive. Created when supernovae collapse, stellar remnant black holes are about 3 to 10 times the mass of our sun. On the other end of the spectrum, supermassive black holes, which lurk in the centers of galaxies, are millions to billions times the mass of our sun.
Should they exist, intermediate-mass black holes would fit somewhere in the middle — 10 to 10,000 times more massive than stellar remnant black holes but not nearly as massive as supermassive black holes. Although these intermediate-mass black holes theoretically should exist, astrophysicists have yet to find indisputable observational evidence.
“Their presence is still debated,” Kıroğlu said. “Astrophysicists have uncovered evidence that they exist, but that evidence can often be explained by other mechanisms. For example, what appears to be an intermediate-mass black hole might actually be the accumulation of stellar-mass black holes.”
To explore the behavior of these evasive objects, Kıroğlu and her team developed new hydrodynamic simulations. First, they created a model of a star, consisting of many particles. Then, they sent the star toward the black hole and calculated the gravitational force acting on the particles during the star’s approach.
“We can calculate specifically which particle is bound to the star and which particle is disrupted (or no longer bound to the star),” Kıroğlu said.
Through these simulations, Kıroğlu and her team discovered that stars could orbit an intermediate-mass black hole as many as five times before finally being ejected. With each pass around the black hole, the star loses more and more of its mass as its ripped apart. Then, the black hole kicks the leftovers — moving at searing speeds — back out into the galaxy. The repeating pattern would create a stunning light show that should help astronomers recognize — and prove the existence of — intermediate-mass black holes.
“It’s amazing that the star isn’t fully ripped apart,” Kıroğlu said. “Some stars might get lucky and survive the event. The ejection speed is so high that these stars could be identified as hyper-velocity stars, which have been observed at the centers of galaxies.”
Next, Kıroğlu plans to simulate different types of stars, including giant stars and binary stars, to explore their interactions with black holes.
Einstein rings modulated by wavelike dark matter from anomalies in gravitationally lensed images
by Alfred Amruth, Tom Broadhurst, Jeremy Lim, Masamune Oguri, George F. Smoot, Jose M. Diego, Enoch Leung, Razieh Emami, Juno Li, Tzihong Chiueh, Hsi-Yu Schive, Michael C. H. Yeung, Sung Kei Li inNature Astronomy
Most of the matter in the universe, amounting to a staggering 85% by mass, cannot be observed and consists of particles not accounted for by the Standard Model of Particle Physics. These particles are known as Dark Matter, and their existence can be inferred from their gravitational effects on light from distant galaxies. Finding the particle that makes up Dark Matter is an urgent problem in modern physics, as it dominates the mass and, therefore, the gravity of galaxies — solving this mystery can lead to new physics beyond the Standard Model.
While some theoretical models propose the existence of ultramassive particles as a possible candidate for Dark Matter, others suggest ultralight particles. A team of astrophysicists led by Alfred AMRUTH, a PhD student in the team of Dr Jeremy LIM of the Department of Physics at The University of Hong Kong (HKU), collaborating with Professor George SMOOT, a Nobel Laureate in Physics from the Hong Kong University of Science and Technology (HKUST) and Dr Razieh EMAMI, a Research Associate at the Center for Astrophysics | Harvard & Smithsonian (CFA), has provided the most direct evidence yet that Dark Matter does not constitute ultramassive particles as is commonly thought but instead comprises particles so light that they travel through space like waves. Their work resolves an outstanding problem in astrophysics first raised two decades ago: why do models that adopt ultramassive Dark Matter particles fail to correctly predict the observed positions and the brightness of multiple images of the same galaxy created by gravitational lensing?
Dark Matter does not emit, absorb or reflect light, which makes it difficult to observe using traditional astronomical techniques. Today, the most powerful tool scientists have for studying Dark Matter is through gravitational lensing, a phenomenon predicted by Albert Einstein in his theory of General Relativity. In this theory, mass causes spacetime to curve, creating the appearance that light bends around massive objects such as stars, galaxies, or groups of galaxies. By observing this bending of light, scientists can infer the presence and distribution of Dark Matter — and, as demonstrated in this study, the nature of Dark Matter itself.
When the foreground lensing object and the background lensed object — both constituting individual galaxies in the illustration — are closely aligned, multiple images of the same background object can be seen in the sky. The positions and brightness of the multiply-lensed images depend on the distribution of Dark Matter in the foreground lensing object, thus providing an especially powerful probe of Dark Matter.
In the 1970s, after the existence of Dark Matter was firmly established, hypothetical particles referred to as Weakly Interacting Massive Particles (WIMPs) were proposed as candidates for Dark Matter. These WIMPs were thought to be ultramassive — more than at least ten times as massive as a proton — and interact with other matter only through the weak nuclear force. These particles emerge from Supersymmetry theories, developed to fill deficiencies in the Standard Model, and have since been widely advocated as the most likely candidate for Dark Matter. However, for the past two decades, adopting ultramassive particles for Dark Matter, astrophysicists have struggled to correctly reproduce the positions and brightness of multiply-lensed images. In these studies, the density of Dark Matter is assumed to decrease smoothly outwards from the centres of galaxies in accordance with theoretical simulations employing ultramassive particles.
Beginning also in the 1970s, but in dramatic contrast to WIMPs, versions of theories that seek to rectify deficiencies in the Standard Model, or those (e.g., String Theory) that seek to unify the four fundamental forces of nature (the three in the Standard Model, along with gravity), advocate the existence of ultralight particles. Referred to as axions, these hypothetical particles are predicted to be far less massive than even the lightest particles in the Standard Model and constitute an alternative candidate for Dark Matter.
According to the theory of Quantum Mechanics, ultralight particles travel through space as waves, interfering with each other in such large numbers as to create random fluctuations in density. These random density fluctuations in Dark Matter give rise to crinkles in spacetime. As might be expected, the different patterns of spacetime around galaxies depending on whether Dark Matter constitutes ultramassive or ultralight particles — smooth versus crinkly — ought to give rise to different positions and brightness for multiply-lensed images of background galaxies.
In work led by Alfred AMRUTH, a PhD student in Dr Jeremy LIM’s team at HKU, astrophysicists have for the first time computed how gravitationally-lensed images generated by galaxies incorporating ultralight Dark Matter particles differ from those incorporating ultramassive Dark Matter particles.
Their research has shown that the general level of disagreement found between the observed and predicted positions as well as the brightness of multiply-lensed images generated by models incorporating ultramassive Dark Matter can be resolved by adopting models incorporating ultralight Dark Matter particles. Moreover, they demonstrate that models incorporating ultralight Dark Matter particles can reproduce the observed positions and brightness of multiply-lensed galaxy images, an important achievement that reveals the crinkly rather than smooth nature of spacetime around galaxies.
‘The possibility that Dark Matter does not comprise ultramassive particles, as has long been advocated by the scientific community, alleviates other problems in both laboratory experiments and astronomical observations,’ explains Dr Lim. ‘Laboratory experiments have been singularly unsuccessful at finding WIMPs, the long-favoured candidate for Dark Matter. Such experiments are in their final stretch, culminating in the planned DARWIN experiment, leaving WIMPs with no place to hide if not found .’
Professor Tom BROADHURST, an Ikerbasque Professor at the University of the Basque Country, a Visiting Professor at HKU, and a co-author of the paper adds, ‘If Dark Matter comprises ultramassive particles, then according to cosmological simulations, there should be hundreds of satellite galaxies surrounding the Milky Way. However, despite intensive searches, only around fifty have been discovered so far. On the other hand, if Dark Matter comprises ultralight particles instead, then the theory of Quantum Mechanics predicts that galaxies below a certain mass simply cannot form owing to the wave interference of these particles, explaining why we observe a lack of small satellite galaxies around the Milky Way.’
‘Incorporating ultralight rather than ultramassive particles for Dark Matter resolve several longstanding problems simultaneously in both particle physics and astrophysics,’ said Amruth Alfred, ‘We have reached a point where the existing paradigm of Dark Matter needs to be reconsidered. Waving goodbye to ultramassive particles, which have long been heralded as the favoured candidate for Dark Matter, may not come easily, but the evidence accumulates in favour of Dark Matter having wave-like properties as possessed by ultralight particles.’ The pioneering work used the supercomputing facilities at HKU, without which this work would not have been possible.
First observations of core-transiting seismic phases on Mars
by Jessica C. E. Irving, Vedran Lekić, Cecilia Durán, Mélanie Drilleau,et al in Proceedings of the National Academy of Sciences
A new study has uncovered intriguing insights into the liquid core at the centre of Mars, furthering understanding of the planet’s formation and evolution.
The research, led by the University of Bristol, reveals the first-ever detections of sound waves travelling into the Martian core. Measurements from this acoustic energy, called seismic waves, indicate its liquid core is slightly denser and smaller than previously thought, and comprises a mixture of iron and numerous other elements. The findings are all the more remarkable, as the research mission was initially only scheduled to last for a little over one Mars year (two Earth years). Despite Martian storms hastening the accumulation of dust and reducing power to the NASA InSight Mars lander, NASA extended its stay, so geophysical data, including signals of marsquakes, continued to be gathered until the end of last year.
Lead author Dr Jessica Irving, Senior Lecturer in Earth Sciences at the University of Bristol, said: “The extra mission time certainly paid off. We’ve made the very first observations of seismic waves travelling through the core of Mars. Two seismic signals, one from a very distant marsquake and one from a meteorite impact on the far side of the planet, have allowed us to probe the Martian core with seismic waves. We’ve effectively been listening for energy travelling through the heart of another planet, and now we’ve heard it.
“These first measurements of the elastic properties of Mars’ core have helped us investigate its composition. Rather than being just a ball of iron, it also contains a large amount of sulfur, as well as other elements including a small amount of hydrogen.”
The team of researchers used data from NASA’s InSight lander, a robotic spacecraft designed to probe the interior of Mars, to compare seismic waves travelling through the planet’s core with those transiting Mars’ shallower regions, and modelled properties of its interior. The InSight lander deployed a broadband seismometer on the Martian surface in 2018, allowing for the detection of seismic events, including marsquakes and meteorite impacts. The multi-disciplinary team of scientists, including seismologists, geodynamicists and mineral physicists, used observations of two seismic events located in the opposite hemisphere from the seismometer to measure the travel times of seismic waves that passed through the core relative to seismic waves that remained in the mantle.
Dr Irving said: “So-called ‘farside’ events, meaning those on the opposite side of the planet to InSight, are intrinsically harder to detect because a great deal of energy is lost or diverted away as waves travel through the planet. We needed both luck and skill to find, and then use, these events. We detected no farside events in the first Martian year of operations. If the mission had ended then, this research couldn’t have happened.
“The sol 976 marsquake was the most distant event found during the mission. The second farside event, S1000a — the first event detected on day 1,000 of operations — was particularly useful because it turned out to be a meteorite impact which we heard all the way through the planet, so we knew where the seismic signals came from. These events came after the Marsquake Service (MQS) had honed their skills on hundreds of days of Martian data; it then took a lot of seismological expertise from across the Insight Team to tease the signals out from the complex seismograms recorded by the lander.”
The authors used these measurements to build models describing physical properties of the core, including its size and elastic wave-speed. The results suggested Mars’ core is slightly denser and smaller than previous estimates, with a radius of approximately 1,780–1,810 km. These findings are consistent with the core having a relatively high fraction of light elements alloyed with iron, including abundant sulfur and smaller amounts of oxygen, carbon and hydrogen.
Co-author Ved Lekic, Associate Professor of Geology at the University of Maryland College Park, in the US, said: “Detecting and understanding waves that travel through the very core of another planet is incredibly challenging, reflecting decades of efforts by hundreds of scientists and engineers from multiple countries. We not only had to utilise sophisticated seismic analysis techniques, but also deploy knowledge of how high pressures and temperatures affect properties of metal alloys, leveraging the expertise of the InSight Team.”
Dr Irving added: “The new results are important for understanding how Mars’ formation and evolution differ from those of Earth. New theories about the formation conditions and building blocks of the red planet will need to be able to match the core’s physical properties as revealed by this new study.”
Kinematic Evidence of an Embedded Protoplanet in HD 142666 Identified by Machine Learning
by J. P. Terry, C. Hall, S. Abreau, S. Gleyzer in The Astrophysical Journal
A University of Georgia research team has confirmed evidence of a previously unknown planet outside of our solar system, and they used machine learning tools to detect it.
A recent study by the team showed that machine learning can correctly determine if an exoplanet is present by looking in protoplanetary disks, the gas around newly formed stars. The newly published findings represent a first step toward using machine learning to identify previously overlooked exoplanets.
“We confirmed the planet using traditional techniques, but our models directed us to run those simulations and showed us exactly where the planet might be,” said Jason Terry, doctoral student in the UGA Franklin College of Arts and Sciences department of physics and astronomy and lead author on the study.
“When we applied our models to a set of older observations, they identified a disk that wasn’t known to have a planet despite having already been analyzed. Like previous discoveries, we ran simulations of the disk and found that a planet could re-create the observation.”
According to Terry, the models suggested a planet’s presence, indicated by several images that strongly highlighted a particular region of the disk that turned out to have the characteristic sign of a planet — an unusual deviation in the velocity of the gas near the planet.
“This is an incredibly exciting proof of concept. We knew from our previous work that we could use machine learning to find known forming exoplanets,” said Cassandra Hall, assistant professor of computational astrophysics and principal investigator of the Exoplanet and Planet Formation Research Group at UGA. “Now, we know for sure that we can use it to make brand new discoveries.”
The discovery highlights how machine learning has the power to enhance scientists’ work, utilizing artificial intelligence as an added tool to expand researchers’ accuracy and more efficiently economize their time when engaged in such a vast endeavor as investigating deep, outer space.The models were able to detect a signal in data that people had already analyzed; they found something that previously had gone undetected.
“This demonstrates that our models — and machine learning in general — have the ability to quickly and accurately identify important information that people can miss. This has the potential to dramatically speed up analysis and subsequent theoretical insights,” Terry said. “It only took about an hour to analyze that entire catalog and find strong evidence for a new planet in a specific spot, so we think there will be an important place for these types of techniques as our datasets get even larger.”
Accurate oxygen abundance of interstellar gas in Mrk 71 from optical and infrared spectra
by Yuguang Chen, Tucker Jones, Ryan Sanders, Dario Fadda, Jessica Sutter, Robert Minchin, Erin Huntzinger, Peter Senchyna, Daniel Stark, Justin Spilker, Benjamin Weiner, Guido Roberts-Borsani in Nature Astronomy
A study using data from telescopes on Earth and in the sky resolves a problem plaguing astronomers working in the infrared and could help make better observations of the composition of the universe with the James Webb Space Telescope and other instruments.
“We’re trying to measure the composition of gases inside galaxies,” said Yuguang Chen, a postdoctoral researcher working with Professor Tucker Jones in the Department of Physics and Astronomy at the University of California, Davis.
Most elements other than hydrogen, helium and lithium are produced inside stars, so the composition and distribution of heavier elements — especially the ratio of oxygen to hydrogen — can help astronomers understand how many and what kinds of stars are being formed in a distant object. Astronomers use two methods to measure oxygen in a galaxy, but unfortunately, they give different results. One common method, collisionally excited lines, gives a strong signal, but the results are thought to be sensitive to temperature changes, Chen said. A second method uses a different set of lines, called recombination lines, which are fainter but not thought to be affected by temperature.
The recombination line method consistently produces measurements about double those from collisionally excited lines. Scientists attribute the discrepancy to temperature fluctuations in gas clouds, but this has not been directly proven, Chen said. Chen, Jones and colleagues used optical and infrared astronomy to measure oxygen abundance in dwarf galaxy Markarian 71, about 11 million light years from Earth. They used archived data from the recently retired SOFIA flying telescope and the retired Herschel Space Observatory, as well as making observations with telescopes at the W.M. Keck Observatory in Mauna Kea, Hawaii.
SOFIA (Stratospheric Observatory For Infrared Astronomy) was a telescope mounted in a Boeing 747 aircraft. By flying at 38,000 to 45,000 feet, the aircraft could get above 99% of the water vapor in Earth’s atmosphere, which effectively blocks infrared light from deep space from reaching ground level. A joint project of NASA and the German space agency, SOFIA made its last operational flight in September 2022 and is now headed for a museum display in Tucson. The Herschel Space Observatory, named after astronomers William and Caroline Herschel, was an infrared space telescope operated by the European Space Agency. It was active from 2009 to 2013.
With data from these instruments, Chen and Jones examined oxygen abundance in Markarian 71 while correcting for temperature fluctuations. They found that the result from collisionally excited infrared lines was still 50% less than that from the recombination line method, even after eliminating the effect of temperature.
“This result is very surprising to us,” Chen said. There is no consensus on an explanation for the discrepancy, he said. The team plans to look at additional objects to figure out what properties of galaxies correlate with this variation, Chen said.
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