Precise modelling of high-speed black hole encounters

Visualization of the computed gravitational waves emitted in the scattering process of two black holes
Quantum Field and String Theory Group / HU

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Applying abstract mathematical structures to real-world phenomena provides new insights into gravitational waves

An international team of researchers, including scientists from the Max Planck Institute for Gravitational Physics in the Potsdam Science Park, is setting new standards for modeling the encounter of black holes at very high speeds.

The new method is based on – so far – abstract mathematical structures, called Calabi-Yau spaces. Applying them to real astrophysical phenomena leads to highly accurate predictions of how black holes and neutron stars are deflected from their initial orbits after their encounter.

The paper, published today in Nature, comes at the right time to meet the growing demand for highly accurate theoretical predictions.

The results could be used to detect gravitational-wave signals in future observing runs of the current network of gravitational-wave detectors, with the planned third generation of ground-based observatories such as the Einstein Telescope and Cosmic Explorer, and with the space-borne Laser Interferometer Space Antenna (LISA).

Source: Max Planck Institute for Gravitational Physics/Research News

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Media Contact:

Dr. Elke Müller
Press Officer AEI Potsdam, Scientific Coordinator
tel +49 331 567-7303
fax +49 331 567-7298
elke.mueller@aei.mpg.de

Publication

Driesse, M.; Jakobsen, G. U.; Klemm, A.; Mogull, G.; Nega, C.; Plefka, J.; Sauer, B.; Usovitsch, J.
Emergence of Calabi-Yau manifolds in high-precision black hole scattering. (2024)

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New insights into black hole scattering and gravitational waves unveiled
Press release by Queen Mary University London

New findings on the scattering of black holes provide an important basis for understanding gravitational waves
Press release by the Humboldt University Berlin

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Black Holes Can Cook for Themselves, Chandra Study Shows

Perseus Cluster & the Centaurus Cluster

Credit: Perseus Cluster: X-ray: NASA/CXC/SAO/V. Olivares et al.; Optical/IR: DSS; H-alpha: CFHT/SITELLE; Centaurus Cluster: X-ray: NASA/CXC/SAO/V. Olivaresi et al.; Optical/IR: NASA/ESA/STScI; H-alpha: ESO/VLT/MUSE; Image Processing: NASA/CXC/SAO/N. Wolk

JPEG (85.8 kb) - Tiff (76.2 MB) - More Images

A Tour of Black Holes Can Cook for Themselves - More Videos

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Astronomers have taken a crucial step in showing that the most massive black holes in the universe can create their own meals. Data from NASA’s Chandra X-ray Observatory and the Very Large Telescope (VLT) provide new evidence that outbursts from black holes can help cool down gas to feed themselves.

This study was based on observations of seven clusters of galaxies. The centers of galaxy clusters contain the universe’s most massive galaxies, which harbor huge black holes with masses ranging from millions to tens of billions of times that of the Sun. Jets from these black holes are driven by the black holes feasting on gas.

These images show two of the galaxy clusters in the study, the Perseus Cluster and the Centaurus Cluster. Chandra data represented in blue reveals X-rays from filaments of hot gas, and data from the VLT, an optical telescope in Chile, shows cooler filaments in red.

The results support a model where outbursts from the black holes trigger hot gas to cool and form narrow filaments of warm gas. Turbulence in the gas also plays an important role in this triggering process.

According to this model, some of the warm gas in these filaments should then flow into the centers of the galaxies to feed the black holes, causing an outburst. The outburst causes more gas to cool and feed the black holes, leading to further outbursts.

This model predicts there will be a relationship between the brightness of filaments of hot and warm gas in the centers of galaxy clusters. More specifically, in regions where the hot gas is brighter, the warm gas should also be brighter. The team of astronomers has, for the first time, discovered such a relationship, giving critical support for the model.

This result also provides new understanding of these gas-filled filaments, which are important not just for feeding black holes but also for causing new stars to form. This advance was made possible by an innovative technique that isolates the hot filaments in the Chandra X-ray data from other structures, including large cavities in the hot gas created by the black hole’s jets.

The newly found relationship for these filaments shows remarkable similarity to the one found in the tails of jellyfish galaxies, which have had gas stripped away from them as they travel through surrounding gas, forming long tails. This similarity reveals an unexpected cosmic connection between the two objects and implies a similar process is occurring in these objects.

This work was led by Valeria Olivares from the University of Santiago de Chile, and was published Monday in Nature Astronomy and is available online. The study brought together international experts in optical and X-ray observations and simulations from the United States, Chile, Australia, Canada, and Italy. The work relied on the capabilities of the MUSE (Multi Unit Spectroscopic Explorer) instrument on the VLT, which generates 3D views of the universe.

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

Quick Look: Black Holes Can Cook for Themselves, Chandra Study Shows

Source: NASA's Chandra X-Ray Observatory

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Visual Description:

This release features composite images shown side-by-side of two different galaxy clusters, each with a central black hole surrounded by patches and filaments of gas. The galaxy clusters, known as Perseus and Centaurus, are two of seven galaxy clusters observed as part of an international study led by the University of Santiago de Chile.

In each image, a patch of purple with neon pink veins floats in the blackness of space, surrounded by flecks of light. At the center of each patch is a glowing, bright white dot. The bright white dots are black holes. The purple patches represent hot X-ray gas, and the neon pink veins represent filaments of warm gas. According to the model published in the study, jets from the black holes impact the hot X-ray gas. This gas cools into warm filaments, with some warm gas flowing back into the black hole. The return flow of warm gas causes jets to again cool the hot gas, triggering the cycle once again.

While the images of the two galaxy clusters are broadly similar, there are significant visual differences. In the image of the Perseus Cluster on the left, the surrounding flecks of light are larger and brighter, making the individual galaxies they represent easier to discern. Here, the purple gas has a blue tint, and the hot pink filaments appear solid, as if rendered with quivering strokes of a paintbrush. In the image of the Centaurus Cluster on the right, the purple gas appears softer, with a more diffuse quality. The filaments are rendered in more detail, with feathery edges, and gradation in color ranging from pale pink to neon red.

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Fast Facts for Perseus Cluster:

Credit: X-ray: NASA/CXC/SAO/V. Olivares et al.; Optical/IR: DSS; H-alpha: CFHT/SITELLE; Image Processing: NASA/CXC/SAO/N. Wolk
Scale: Image is about 6.4 arcmin (450,000 light-years) across.
Category: Groups and Clusters of Galaxies
Coordinates (J2000): RA 3h 19m 47.71 | Dec +41° 31´ 15.8"
Constellation: Perseus
Observation Dates: 29 observations between Sep 20, 1999 and Nov 7, 2016
Observation Time: 416 hours 45 minutes (17 days 8 hours 45 minutes)

Obs. ID: 428, 502, 503, 3209, 3404, 1513, 4289, 4946, 4947, 3939-4953, 6139, 6145, 6146, 11713-11716, 12025, 12033, 12036, 12037, 19568, 19913-19915

Instrument: ACIS
References: Olivares, V. et al. 2025, Nature Astronomy; arXiv:2501.01902
Color Code: X-ray: blue; Optical: red, green, blue; H-alpha: red
Distance Estimate: About 240 million light-years from Earth

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Fast Facts for Centaurus Cluster:

Credit: X-ray: NASA/CXC/SAO/V. Olivaresi et al.; Optical/IR: NASA/ESA/STScI; H-alpha: ESO/VLT/MUSE; Image Processing: NASA/CXC/SAO/N. Wolk
Scale: Image is about 1.4 arcmin (57,000 light-years) across.
Category: Groups and Clusters of Galaxies
Coordinates (J2000): RA 12h 48m 49.2s | Dec -41° 18´ 43.8"
Constellation: Centaurus
Observation Dates: 16 observations from May 22, 2000 to Jun 05, 2014
Observation Time: 240 hours 1 minute (10 days 1 minutes)
Obs. ID: 504 ,505 ,1560 ,4190, 4191, 4954, 4955 ,5310, 16223-16225 ,16534 ,16607-16610
Instrument: ACIS
References: Olivares, V. et al. 2025, Nature Astronomy; arXiv:2501.01902
Color Code: X-ray: blue; Optical/IR: red, green, blue; H-alpha: red
Distance Estimate: About 145 million light-years from Earth

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Massive black hole in the early universe spotted taking a ‘nap’ after overeating

Computer-simulated image of a supermassive black hole at the core of a galaxy.
Credit: NASA, ESA, and D. Coe, J. Anderson, and R. van der Marel (STScI)

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Gravitational waves data held clues for high-mass black holes’ violent beginnings

The size and spin of black holes can reveal important information about how and where they formed, according to new research. The study tests the idea that many of the black holes observed by astronomers have merged multiple times within densely populated environments containing millions of stars.

The team, involving researchers from the University of Cambridge, examined the public catalogue of 69 gravitational wave events involving binary black holes detected by The Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo Observatory for clues about these successive mergers, which they believe create black holes with distinctive spin patterns.

They discovered that a black hole’s spin changes when it reaches a certain mass, suggesting it may have been produced through a series of multiple previous mergers.

Their study, published in the journal Physical Review Letters, shows how spin measurements can reveal the formation history of a black hole and offers a step forward in understanding the diverse origins of these astrophysical phenomena.

“As we observe more black hole mergers with gravitational wave detectors like LIGO and Virgo, it becomes ever clearer that black holes exhibit diverse masses and spins, suggesting they may have formed in different ways,” said lead author Dr Fabio Antonini from Cardiff University. “However, identifying which of these formation scenarios is most common has been challenging.”

The team pinpointed a clear mass threshold in the gravitational waves data where black hole spins consistently change.

They say this pattern aligns with existing models which assume black holes are produced through repeat collisions in clusters, rather than other environments where spin distributions are different.

This result supports a robust and relatively model-independent signature for identifying these kinds of black holes, something that has been challenging to confirm until now, according to the team.

“Our study gives us a powerful, data-driven way to identify the origins of a black hole’s formation history, showing that the way it spins is a strong indicator of it belonging to a group of high-mass black holes, which form in densely populated star clusters where small black holes repeatedly collide and merge with one another,” said co-author Dr Isobel Romero-Shaw, from Cambridge’s Department of Applied Mathematics and Theoretical Physics.

Their study will now help astrophysicists further refine computer models which simulate the formation of black holes, helping to shape how future gravitational wave detections are interpreted.

“Collaborating with other researchers and using advanced statistical methods will help to confirm and expand our findings, especially as we move toward next-generation detectors,” said co-author Dr Thomas Callister from the University of Chicago. “The Einstein Telescope, for example, could detect even more massive black holes and provide unprecedented insights into their origins.”

Reference:

Fabio Antonini, Isobel M. Romero-Shaw, and Thomas Callister. 'Star Cluster Population of High Mass Black Hole Mergers in Gravitational Wave Data.' Physical Review Letters (2025). DOI: 10.1103/PhysRevLett.134.011401

Source: University of Cambridge/News

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Note: The text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright ©University of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

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NASA's Hubble Takes the Closest-Ever Look at a Quasar

Quasar 3C 273

A Hubble Space Telescope image of the core of quasar 3C 273. A coronagraph on Hubble blocks out the glare coming from the supermassive black hole at the heart of the quasar. This allows astronomers to see unprecedented details near the black hole such as weird filaments, lobes, and a mysterious L-shaped structure, probably caused by small galaxies being devoured by the black hole. Located 2.5 billion light-years away, 3C 273 is the first quasar (quasi-stellar object) ever discovered, in 1963. Credits/Image: NASA, ESA, Bin Ren (Université Côte d’Azur/CNRS); Acknowledgment: John Bahcall (IAS); Image Processing: Joseph DePasquale (STScI)

Astronomers have used the unique capabilities of NASA's Hubble Space Telescope to peer closer than ever into the throat of an energetic monster black hole powering a quasar. A quasar is a galactic center that glows brightly as the black hole consumes material in its immediate surroundings.

The new Hubble views of the environment around the quasar show a lot of "weird things," according to Bin Ren of the Côte d'Azur Observatory and Université Côte d'Azur in Nice, France. "We've got a few blobs of different sizes, and a mysterious L-shaped filamentary structure. This is all within 16,000 light-years of the black hole."

Some of the objects could be small satellite galaxies around the black hole, and so they could offer the materials that will accrete onto the central super massive black hole, powering the bright lighthouse. "Thanks to Hubble's observing power, we're opening a new gateway into understanding quasars," said Ren. "My colleagues are excited because they've never seen this much detail before."

Quasars look starlike as point sources of light in the sky (hence the name quasi-stellar object). The quasar in the new study, 3C 273, was identified in 1963 by astronomer Maarten Schmidt as the first quasar. At a distance of 2.5 billion light-years it was too far away for a star. It must have been more energetic than ever imagined, with a luminosity over 10 times brighter than the brightest giant elliptical galaxies. This opened the door to an unexpected new puzzle in cosmology: What is powering this massive energy production? The likely culprit was material accreting onto a black hole.

In 1994 Hubble's new sharp view revealed that the environment surrounding quasars is far more complex than first suspected. The images suggested galactic collisions and mergers between quasars and companion galaxies, where debris cascades down onto supermassive black holes. This reignites the giant black holes that drive quasars.

For Hubble, staring into the quasar 3C 273 is like looking directly into a blinding car headlight and trying to see an ant crawling on the rim around it. The quasar pours out thousands of times the entire energy of stars in a galaxy. One of closest quasars to Earth, 3C 273 is 2.5 billion light-years away. (If it was very nearby, a few tens of light-years from Earth, it would appear as bright as the Sun in the sky!) Hubble's STIS instrument can serve as a coronagraph to block light from central sources, not unlike how the Moon block the Sun's glare during a total solar eclipse. Astronomers have used STIS to unveil dusty disks around stars to understand the formation of planetary systems, and now they can use STIS to better understand quasars’ host galaxies. The Hubble coronograph allowed astronomers to look eight times closer to the black hole than ever before.

Scientists got rare insight into the quasar's 300,000-light-year-long extragalactic jet of material blazing across space at nearly the speed of light. By comparing the STIS coronagraphic data with archival STIS images with a 22-year separation, the team led by Ren concluded that the jet is moving faster when it is farther away from the monster black hole.

"With the fine spatial structures and jet motion, Hubble bridged a gap between the small-scale radio interferometry and large-scale optical imaging observations, and thus we can take an observational step towards a more complete understanding of quasar host morphology. Our previous view was very limited, but Hubble is allowing us to understand the complicated quasar morphology and galactic interactions in detail. In the future, looking further at 3C 273 in infrared light with the James Webb Space Telescope might give us more clues," said Ren.

At least 1 million quasars are scattered across the sky. They are useful background "spotlights" for a variety of astronomical observations. Quasars were most abundant about 3 billion years after the big bang, when galaxy collisions were more common.

The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute (STScI) in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.

Source: HubbleSite/News

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About This Release

Credits:

Media Contact:

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland

Science Contact:

Bin Ren
Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, France

Permissions: Content Use Policy

Contact Us: Direct inquiries to the News Team.

Related Links and Documents

• Science Paper: The science paper by Bin Ren et al., PDF (8.06 MB)
• NASA's Hubble Portal

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How galaxies make black holes collide

Schematic overview of a wide binary orbiting inside the Milky Way. While moving through the Galaxy its ellipticity gets modulated by the gravity of the Galaxy and fly-bys from ambient stars, leading to close encounters (inset). Credit: Jakob Stegmann et al 2024 ApJL 972 L19

Illustration of two equal-mass objects moving around each other on a circular orbit (left panel) and more and more elliptical orbits (towards the right). While all objects remain widely separated for most of the time, those moving on a very elliptical trajectory encounter each other very closely once per orbit. Credit: A. Price-Whelan/Creative Commons CC-BY-SA licence

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The groundbreaking detections of gravitational waves from merging pairs of black holes have left us with an intriguing question: how do black holes get close enough to merge? Scientists at MPA show that some of them may have started out as massive stars orbiting one another at extremely large separations — 1,000 to 10,000 times the distance between Earth and Sun. Once these stars end their lives and form black holes, the gravity of the entire galaxy in which they reside could slowly deform the shape of their orbit leading to a close encounter and merger of the black holes.

A large fraction of stars are not alone. Observations show that, unlike our Sun, many of them are orbited by a stellar companion and form a so-called binary. The separation at which these binary stars orbit one another closely determines their evolution. On the one hand, stars on very tight orbits are prone to exchange mass leading to a complex interactive stellar evolution. For massive stars, these interactions may leave behind a close binary black hole which could eventually merge due to the energy-loss from gravitational-wave emission. On the other hand, binary stars at wider separations were previously thought to evolve rather unspectacularly, effectively as single stars, leaving behind binary black holes which are too far apart to merge.

In a recent study, published in the The Astrophysical Journal Letters, a group of researchers led by MPA research fellow Jakob Stegmann question this standard lore of binary physics and show that it is only true as long as the binaries are considered to be in isolation. In reality, they are embedded in a galactic environment in which wide binaries separated by more than 1,000 Earth-Sun distances are vulnerable to perturbations from the gravity of the host galaxy and from fly-bys of ambient stars. Taking into account this galactic influence, the study shows that the dynamics of wide binaries can give rise to extreme interactions between stars and compact remnants.

These interactions are a consequence of the extremely low binding energy that holds very wide binary black holes together. Thus, the gravitational pull of the entire host galaxy can slowly deform the shape of the orbit on which the two black holes move around each other and make it more and more elongated. On these highly elliptical orbits the two black holes remain widely separated for most of the time, but pass close to each other once per orbit (see animation). This leads to a counterintuitive result: In order to bring two black holes closer than a few kilometres so that they can merge, we could nevertheless start with a wide separation of more than 1,000 times the distance between Earth and Sun. The clue lies in the ellipticity of their orbit which slowly grows due to the disturbing effect of the galaxy’s gravity.

This mechanism of driving two black holes closer together could also be relevant for the evolution of wide low-mass binary stars. Recently, researchers at MPIA in Heidelberg have searched for wide binaries in the data from the ESA-led mission Gaia. Surprisingly, they found that about ten percent of all low-mass stars possess a distant stellar companion. While systems like those are not massive enough to develop black holes, in this case the MPA study shows that the gravity of the galaxy could drive the stars to a head-on collision. These collisions would not lead to detectable emission of gravitational waves, but could be visible as energetic flares, so-called Luminous Red Novae.

The results of this study represent progress in investigating the plethora of evolutionary pathways of binary stars and their compact remnants. While previous work on wide binaries has mostly focused on ruling out the existence of a distant companion to our Sun (referred to as the “Nemesis hypothesis”), on the one hand, and understanding the upper limit of their separation to remain bound, on the other hand, little attention has been paid to studying the interactions between wide binary stars. With future data releases of Gaia expanding the catalogue of wide binary stars at an unprecedented rate, the MPA study makes an important step towards understanding their co-evolution with the Milky Way. Investigating their dynamics in detail allows us to understand how systems previously thought uneventful could in fact lead to some of the most energetic transients in the Universe.

Source: Max Planck Institute for Astrophysics/News

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Author:

Jakob Stegmann
tel:2237
stegmaja@mpa-garching.mpg.de

Original Publication

Jakob Stegmann, Alejandro Vigna-Gómez, Antti Rantala, Tom Wagg, Lorenz Zwick, Mathieu Renzo, Lieke A. C. van Son, Selma E. de Mink, and Simon D. M. White

Close Encounters of Wide Binaries Induced by the Galactic Tide: Implications for Stellar Mergers and Gravitational-wave Sources

https://iopscience.iop.org/article/10.3847/2041-8213/ad70bb

Source | DOI

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NSF–DOE Rubin Observatory’s Unparalleled Vision Will Revolutionize Multi-Messenger Astronomy

PR Image noirlab2421a
Artist’s Illustration of Multi-Messenger Event

PR Image noirlab2421b
Night Light

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Vera C. Rubin Observatory will unite coordinated observations of cosmic phenomena using the four messengers of the Universe

Photons, neutrinos, cosmic rays and gravitational waves all carry information about the Universe. Multi-messenger astronomy brings together these four signals to investigate astronomical events from multiple cosmic perspectives. With its sensitive camera and suite of filters, NSF–DOE Vera C. Rubin Observatory will increase the population of known multi-messenger sources by obtaining crucial color information and localizing events for follow-up observations by other telescopes.

Astronomy has always relied on light to convey information about the Universe. But capturing photons is no longer the only technique scientists have for studying astronomical phenomena. Subatomic particles, such as neutrinos and those that are delivered in the form of cosmic rays, as well as gravitational waves — ripples in the fabric of space-time — are also messengers. Multi-messenger astronomy aims to combine the information from more than one of these signals to give researchers a deeper understanding of some of the most extreme events in the Universe. NSF–DOE Vera C. Rubin Observatory will soon contribute to this emerging field by using its powerful camera and wide field of view to find faint multi-messenger sources and point other telescopes in the right direction for follow-up observations.

Rubin Observatory is jointly funded by the U.S. National Science Foundation (NSF) and the U.S. Department of Energy, Office of Science (DOE/SC). It is a Program of NSF NOIRLab, which, along with SLAC National Accelerator Laboratory, will jointly operate Rubin.

Multi-messenger astronomy is an enhanced way of studying cosmic events that are predicted to emit more than one type of signal, such as stellar explosions, actively feeding black holes, and collisions between compact objects, to name just a few. Each messenger communicates unique information about the physical processes and energies involved. When a single source is observed using multiple signals the data can be combined to reach a deeper level of insight. “The result is more than the sum of its parts,” says Raffaella Margutti, associate professor at the University of California at Berkeley.

In addition to conducting a massive study of the southern sky called the Legacy Survey of Space and Time (LSST), Rubin will also perform ‘Target of Opportunity’ observations in quick response to alerts of potential multi-messenger sources. As the fastest-slewing large telescope in the world, Rubin can point to targets in as little as three minutes. Such observations will provide crucial information about an event’s optical — meaning wavelengths detectable by the human eye — properties, which in turn helps localize the event for follow-up by other telescopes.

However, in order to coordinate multiple telescopes capable of detecting the different types of messengers, scientists have to know where to look. Signals such as gravitational waves and neutrinos can point scientists in the general direction of a source, but in order to pinpoint its exact location you need light. This is where Rubin, equipped with the largest and most sensitive camera ever built for astronomy and astrophysics, will shine.

Margutti, whose studies focus specifically on finding the electromagnetic counterparts to gravitational wave events, explains, “Gravitational wave observatories can only tell you ‘look at this large area and search for something very faint.’ But you don't know exactly where to look.” Furthermore, the distance at which current observatories are capable of detecting gravitational waves can be far beyond the limit of what they can detect with photons, making it hard to observe an event with both messengers.

With its deep and wide capabilities, Rubin will help mitigate both of these challenges. “Rubin wins twice,” says Margutti. “Its strong light-collecting power and ability to scan large sections of sky mean it’s very sensitive to faint optical signals, like those we would be seeking from a gravitational wave source.”

So far only one multi-messenger gravitational wave event has been observed: a merger between two neutron stars that sent both space-time ripples and photons careening across the cosmos. Other events predicted to emit more than one messenger are black hole-neutron star and black hole-black hole mergers. “I would be super excited if we found photons coming from these types of mergers,” says Margutti. “Rubin is uniquely positioned to confirm or expand on the types of mergers that produce light.”

Rubin’s ability to detect faint sources will also be a game changer for studying neutrinos. Robert Stein, California Institute of Technology postdoctoral scholar, explains: “In neutrino science there are many different types of possible sources, but existing optical telescopes are only able to see the brightest, most unusual ones.” Based on the number of neutrinos arriving at detectors here on Earth, scientists believe there to be a vast population of neutrino sources at varying distances throughout the Universe. However, given the limits of existing telescopes, Stein estimates that only 5–10% of them are also detectable with photons. By bringing myriad faint sources to light for the very first time, Rubin could increase that to 50%.

“Neutrino science is in its infancy, so our list of possible sources is still emerging,” says Stein. “In ten or fifteen years we will likely discover that events we’ve already known about are also neutrino source populations.”

Margutti and Stein are both confident that the overarching power of Rubin in the era of multi-messenger astronomy will be in uncovering the unexpected. As it covers vast swaths of the southern hemisphere sky, there’s no telling what Rubin’s unparalleled vision is going to reveal. “The best use of Rubin is as a discovery machine,” says Margutti. Stein echoes a similar sentiment, saying, “I hope to learn what new types of sources we should investigate next. If Rubin could give us that clarity, and I believe it will, that would be amazing.”

Source: NSF’s National Optical-Infrared Astronomy Research Laboratory (NOIRLab)/News

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More information

The NSF–DOE Rubin Observatory is a joint initiative of the U.S. National Science Foundation (NSF) and the Department of Energy (DOE). Its primary mission is to carry out the Legacy Survey of Space and Time, providing an unprecedented data set for scientific research supported by both agencies. Rubin is operated jointly by NSF NOIRLab and SLAC National Accelerator Laboratory (SLAC). NOIRLab is managed for NSF by the Association of Universities for Research in Astronomy (AURA) and SLAC is operated for DOE by Stanford University. France provides key support to the construction and operations of Rubin Observatory through contributions from CNRS/IN2P3. Additional contributions from a number of international organizations and teams are acknowledged.

The U.S. National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future.

NSF NOIRLab (U.S. National Science Foundation National Optical-Infrared Astronomy Research Laboratory), the U.S. center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (in cooperation with DOE’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively.

SLAC National Accelerator Laboratory is a vibrant multiprogram laboratory that explores how the Universe works at the biggest, smallest, and fastest scales and invents powerful tools used by scientists around the globe. With research spanning particle physics, astrophysics and cosmology, materials, chemistry, bio- and energy sciences and scientific computing, SLAC helps solve real-world problems and advance the interests of the nation.

SLAC is operated by Stanford University for the U.S. Department of Energy’s Office of Science. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time.

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Links

• Vera C. Rubin Observatory website
• Vera C. Rubin Observatory images
• More Rubin images
• Rubin videos
• Rubin multimedia resources

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Contacts

Raffaella Margutti
Associate Professor
University of California Berkeley
Email: rmargutti@berkeley.edu

Robert Stein
Postdoctoral Scholar
California Institute of Technology
Email: rdstein@caltech.edu

Bob Blum
Director for Operations
Vera C. Rubin Observatory / NSF NOIRLab
Tel: +1 520-318-8233
Email: bob.blum@noirlab.edu

Željko Ivezić
Director of Rubin Construction
Professor of Astronomy, University of Washington / AURA
Tel: +1-206-403-6132
Email: ivezic@uw.edu

Josie Fenske
Jr. Public Information Officer
NSF NOIRLab
Email: josie.fenske@noirlab.edu

Manuel Gnida
Head of External Communications
SLAC National Accelerator Laboratory
Tel: +1 650-926-2632 (office)
Cell: +1 415-308-7832 (cell)
Email: mgnida@slac.stanford.edu

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Scientist performs the first nonlinear study of black hole mimickers

Gravitational waves emitted from a black hole mimicker at the center. Brighter colors indicate higher amplitudes of the waves. The semi-circles expand over time as the waves propagate outward. Credit: Nils Siemonsen.

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In recent research, a scientist from Princeton University has performed the first nonlinear study of the merger of a black hole mimicker, aiming to understand the nature of gravitational wave signals emitted by these objects, which could potentially help to identify black holes more accurately.

Black hole mimickers are hypothetical astronomical objects that mimic black holes, specifically in their gravitational wave signals and their effect on surrounding objects. However, they lack an event horizon, which is the point of no return.

The research was conducted by Nils Siemonsen, Associate Research Scholar at Princeton University, who spoke to Phys.org about his work.

"Black hole mimickers are objects remarkably close to black holes but lacking an event horizon. Observationally, we may be able to distinguish black holes from objects mimicking most of their properties using gravitational wave observations," he said.

The study, published in Physical Review Letters, focuses on a type of black hole mimicker called boson stars. The key to distinguishing them from black holes, according to Dr. Siemonsen, lies in the gravitational waves emitted when boson stars collide and merge.

Binary boson stars and mergers

Boson stars are one of the potential candidates for black hole mimickers, and as the name suggests, consist of bosons. Bosons are subatomic particles, like photons and the Higgs particle.

Boson stars consist of scalar bosons like the hypothetical axions, which are bosons with no spin, meaning they have no intrinsic angular momentum. The scalar fields of the particles form a gravitationally bound, stable configuration without needing strong interaction.

Previous research has shown that the merger of a binary boson star system leads to gravitational wave signals, which are ripples in spacetime caused by violent processes.

These signals are universally identical to that of a black hole ringdown (or the post-merger phase) independently of the black hole mimicker's internal structure.

The difference in the emitted gravitational wave signals is seen after a light-crossing time of the interior of the mimicker, which is the time taken by light to travel the diameter of the mimicker, which in this case is the boson star.

In the case of a black hole mimicker, this is characterized by repeated burst-like gravitational echoes.

In aiming to refine earlier research, Dr. Siemonsen sought to address issues like the lack of consideration for nonlinear gravitational effects and the exclusion of self-interactions among the matter of the object.

Nonlinear and self-consistent treatment of black hole mimickers

To address the limitations of the previous studies, Dr. Siemonsen used numerical simulations to solve the full Einstein-Klein-Gordon equations, which describe the evolution of scalar fields, such as those in boson stars.

For the merger, the study focused on large mass-ratio scenarios, i.e., the merger of a smaller boson star with a larger, more compact one, with the Klein-Gordon equations describing the head-on collision of the binary star system.

The Klein-Gordon equation, coupled with Einstein's field equations, which describe the gravitational dynamics, allows for the study of the self-consistent evolution of the system.

For solving the set of equations, Dr. Siemonsen used the Newton-Raphson relaxation technique with the fifth-order finite difference methods.

He explained the challenges with implementing these techniques: "Only under certain conditions does a black hole mimicker form from the merger of two boson stars. The region in the solution, where this occurs, is particularly challenging to simulate due to the large separation of scales."

To overcome these, methods like adaptive mesh refinement and very high resolution were used.

High frequency bursts

The simulations revealed that the gravitational wave signal of the ringdown contains a burst-like component with different properties, as previously believed, as well as a long-lived gravitational wave component.

"Neither of these components are present in a regular binary black hole merger and ringdown. This may guide future gravitational wave searches focusing on testing the black hole paradigm," explained Dr. Siemonsen.

However, the initial gravitational wave signal of a mimicker is similar to that of a rotating black hole, known as a Kerr black hole, as the primary (or larger) boson star becomes more compact and dense.

The study found that the timings of the bursts depend on the size of the smaller boson star involved in the merger.

Additionally, they found a long-lived component with a frequency comparable to what would be expected from a black hole, likely due to oscillations of the remnant object.

"Black holes settle down to their quiescent state over very short timescales. Black hole mimickers, on the other hand, are generically believed to re-emit some of the available energy at the merger in the form of gravitational waves during the latter's ringdown over relatively long timescales," explained Dr. Siemonsen.

Finally, the study revealed that the total energy emitted in the gravitational waves is significantly larger than expected from an equivalent black hole merger event.

Future work

The two components identified in the study could be used as a differentiator between a black hole merger remnant and a black hole mimicker.

"However, there are still many unanswered questions about properties of well-motivated black hole mimickers and their merger and ringdown dynamics," added Dr. Siemonsen.

Speaking of future work, he noted, "One interesting future direction is to consider a well-motivated black hole mimicker and understand its inspiral, merger, and ringdown dynamics in the context of a binary.

"Furthermore, analyzing the ringdown of these well-motivated mimickers using perturbative techniques and connecting these to nonlinear treatments is crucial to guide future tests of the black hole paradigm using gravitational wave observations."

by Tejasri Gururaj , Phys.org

Source: Phys.org/Space News

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More information: Nils Siemonsen, Nonlinear Treatment of a Black Hole Mimicker Ringdown, Physical Review Letters (2024). DOI: 10.1103/PhysRevLett.133.031401. On arXiv: DOI: 10.48550/arxiv.2404.14536

Journal information: Physical Review Letters, arXiv

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Explore further:

• Identification of kick velocity large enough for individual gravitational wave event following binary black hole merger

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Exotic black holes could be a byproduct of dark matterJune 6, 2024

Depiction of a primordial black hole forming amid a sea of hot, color-charged quarks and gluons, a tiny fraction of a second after the Big Bang. Credit: Image by Kaća Bradonjić

In the first quintillionth of a second, the universe may have sprouted microscopic black holes with enormous amounts of nuclear charge, MIT physicists propose.

For every kilogram of matter that we can see — from the computer on your desk to distant stars and galaxies — there are 5 kilograms of invisible matter that suffuse our surroundings. This “dark matter” is a mysterious entity that evades all forms of direct observation yet makes its presence felt through its invisible pull on visible objects.

Fifty years ago, physicist Stephen Hawking offered one idea for what dark matter might be: a population of black holes, which might have formed very soon after the Big Bang. Such “primordial” black holes would not have been the goliaths that we detect today, but rather microscopic regions of ultradense matter that would have formed in the first quintillionth of a second following the Big Bang and then collapsed and scattered across the cosmos, tugging on surrounding space-time in ways that could explain the dark matter that we know today.

Now, MIT physicists have found that this primordial process also would have produced some unexpected companions: even smaller black holes with unprecedented amounts of a nuclear-physics property known as “color charge.”

These smallest, “super-charged” black holes would have been an entirely new state of matter, which likely evaporated a fraction of a second after they spawned. Yet they could still have influenced a key cosmological transition: the time when the first atomic nuclei were forged. The physicists postulate that the color-charged black holes could have affected the balance of fusing nuclei, in a way that astronomers might someday detect with future measurements. Such an observation would point convincingly to primordial black holes as the root of all dark matter today.

“Even though these short-lived, exotic creatures are not around today, they could have affected cosmic history in ways that could show up in subtle signals today,” says David Kaiser, the Germeshausen Professor of the History of Science and professor of physics at MIT. “Within the idea that all dark matter could be accounted for by black holes, this gives us new things to look for.”

Kaiser and his co-author, MIT graduate student Elba Alonso-Monsalve, have published their study today  (June 6,2024) in the journal Physical Review Letters.

A time before stars

The black holes that we know and detect today are the product of stellar collapse, when the center of a massive star caves in on itself to form a region so dense that it can bend space-time such that anything — even light — gets trapped within. Such “astrophysical” black holes can be anywhere from a few times as massive as the sun to many billions of times more massive.

“Primordial” black holes, in contrast, can be much smaller and are thought to have formed in a time before stars. Before the universe had even cooked up the basic elements, let alone stars, scientists believe that pockets of ultradense, primordial matter could have accumulated and collapsed to form microscopic black holes that could have been so dense as to squeeze the mass of an asteroid into a region as small as a single atom. The gravitational pull from these tiny, invisible objects scattered throughout the universe could explain all the dark matter that we can’t see today.

If that were the case, then what would these primordial black holes have been made from? That’s the question Kaiser and Alonso-Monsalve took on with their new study.

“People have studied what the distribution of black hole masses would be during this early-universe production but never tied it to what kinds of stuff would have fallen into those black holes at the time when they were forming,” Kaiser explains.

Super-charged rhinos

The MIT physicists looked first through existing theories for the likely distribution of black hole masses as they were first forming in the early universe.

“Our realization was, there’s a direct correlation between when a primordial black hole forms and what mass it forms with,” Alonso-Monsalve says. “And that window of time is absurdly early.”

She and Kaiser calculated that primordial black holes must have formed within the first quintillionth of a second following the Big Bang. This flash of time would have produced “typical” microscopic black holes that were as massive as an asteroid and as small as an atom. It would have also yielded a small fraction of exponentially smaller black holes, with the mass of a rhino and a size much smaller than a single proton.

What would these primordial black holes have been made from? For that, they looked to studies exploring the composition of the early universe, and specifically, to the theory of quantum chromodynamics (QCD) — the study of how quarks and gluons interact.

Quarks and gluons are the fundamental building blocks of protons and neutrons — elementary particles that combined to forge the basic elements of the periodic table. Immediately following the Big Bang, physicists estimate, based on QCD, that the universe was an immensely hot plasma of quarks and gluons that then quickly cooled and combined to produce protons and neutrons.

The researchers found that, within the first quintillionth of a second, the universe would still have been a soup of free quarks and gluons that had yet to combine. Any black holes that formed in this time would have swallowed up the untethered particles, along with an exotic property known as “color charge” — a state of charge that only uncombined quarks and gluons carry.

“Once we figured out that these black holes form in a quark-gluon plasma, the most important thing we had to figure out was, how much color charge is contained in the blob of matter that will end up in a primordial black hole?” Alonso-Monsalve says.

Using QCD theory, they worked out the distribution of color charge that should have existed throughout the hot, early plasma. Then they compared that to the size of a region that would collapse to form a black hole in the first quintillionth of a second. It turns out there wouldn’t have been much color charge in most typical black holes at the time, as they would have formed by absorbing a huge number of regions that had a mix of charges, which would have ultimately added up to a “neutral” charge.

But the smallest black holes would have been packed with color charge. In fact, they would have contained the maximum amount of any type of charge allowed for a black hole, according to the fundamental laws of physics. Whereas such “extremal” black holes have been hypothesized for decades, until now no one had discovered a realistic process by which such oddities actually could have formed in our universe.

Professor Bernard Carr of Queen Mary University of London, an expert on the topic of primordial black holes who first worked on the topic with Stephen Hawking, describes the new work as “exciting.” Carr, who was not involved in the study, says the work “shows that there are circumstances in which a tiny fraction of the early universe can go into objects with an enormous amount of color charge (at least for a while), exponentially greater than what has been identified in previous studies of QCD.”

The super-charged black holes would have quickly evaporated, but possibly only after the time when the first atomic nuclei began to form. Scientists estimate that this process started around one second after the Big Bang, which would have given extremal black holes plenty of time to disrupt the equilibrium conditions that would have prevailed when the first nuclei began to form. Such disturbances could potentially affect how those earliest nuclei formed, in ways that might some day be observed.

“These objects might have left some exciting observational imprints,” Alonso-Monsalve muses. “They could have changed the balance of this versus that, and that’s the kind of thing that one can begin to wonder about.”

This research was supported, in part, by the U.S. Department of Energy. Alonso-Monsalve is also supported by a fellowship from the MIT Department of Physics.

 

Jennifer Chu | MIT News 

Paper: “Primordial Black Holes with QCD Color Charge”

Source: Massachusetts Institute of Technology (MIT)/News

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NASA's Roman Space Telescope Could Help Researchers Detect the Universe’s First Stars

Tidal Disruption of a Star (Artist’s Concept)
Credits: Illustration: Ralf Crawford (STScI)

Images

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The first stars to form in the universe were very different from our Sun. Known to astronomers (somewhat paradoxically) as Population III, or Pop III, stars, they were made almost entirely of hydrogen and helium. They are believed to have been much larger, hotter, and more massive than our Sun. As a result, Pop III stars use their fuel more quickly and have shorter lifespans.

Pop III stars, which came about in the first few hundred million years after the big bang, are crucial in understanding the development of the universe. These stars were the nuclear furnaces where the first elements heavier than helium, which astronomers call metals, were generated, and ultimately are the reason for the complex systems of galaxies in the current universe.

No Pop III stars are found around us today, so to learn about them we must look back to the early universe. NASA’s Nancy Grace Roman Space Telescope will provide a panoramic field of view 200 times larger than the infrared view of the sky from NASA’s Hubble Space Telescope and survey the sky 1,000 times faster. As a result, Roman may be a key tool for helping astronomers see this rare first generation of stars after it launches by May 2027.

Shredded Stars

The new approach will not seek intact stars. Instead, astronomers will hunt for signs of Pop III stars that have been shredded by black holes, creating a bright and energetic phenomenon known as a tidal disruption event (TDE).

If a star moves close enough to a black hole, the star will experience gravitational tides strong enough to completely disrupt it. Some of the material from the disrupted star then collects into an accretion disk, where complex physical processes cause it to glow brightly enough to be seen from billions of light-years away.

"Since we know that black holes likely exist at these early epochs, catching them as they’re devouring these first stars might offer us the best shot to indirectly detect Pop III stars," noted Priyamvada Natarajan of Yale University, a co-author of the study.

TDEs generate light in many wavelengths, including X-ray, radio, ultraviolet (UV), and optical light. The further we look into the early universe, where these early stars primarily reside, the more the optical and UV light is redshifted, or stretched by the expanding universe, into near-infrared wavelengths visible to Roman.

Not only does the wavelength of light stretch – so does the observed timescale of the TDE. Like an exploding star or supernova, a TDE is a transient event that increases quickly in brightness and then gradually decreases over time. But due to the large redshift of these events, a Pop III TDE would brighten over the course of hundreds to thousands of days, while its decline would last more than a decade.

“The evolution timescales of Pop III TDEs are very long, which is one feature that could distinguish a Pop III TDE from other transients including supernovas and TDEs of current-generation stars like our Sun,” said Rudrani Kar Chowdhury, postdoctoral fellow of the University of Hong Kong and first author of the study.

“Since they last for a longer time, a Pop III TDE might be easier to detect, but it might be harder to identify as a transient,” added co-author Jane Dai, professor of astrophysics at the University of Hong Kong. “Scientists would need to design the right survey strategy.”

A Coordinated Hunt

While NASA’s James Webb Space Telescope is powerful enough to detect and study TDEs in the early universe, its field of view is too small to make it an efficient TDE hunter. Of Roman’s core community surveys, the most promising for finding TDEs is the High Latitude Wide Area survey, which aims to cover approximately 2,000 square degrees of the sky outside of the plane of our galaxy.

“Roman can go very deep and yet cover a very big area of the sky. That's what's needed to detect a meaningful sample of these TDEs,” said Dai.

Webb would be useful for follow-up observations, however, particularly with its suite of spectroscopic tools. Once Roman detects these TDEs, Webb’s instruments could identify if any metals are present.

“Since these stars are only made up of hydrogen and helium, we will not see any metal lines in the spectrum of objects, whereas in the spectra of TDEs from regular stars we can see various metal lines,” Kar Chowdhury noted.

With this proposed strategy for identifying Pop III stars, there’s an opportunity to explore more of the universe’s mysteries, opening up numerous opportunities to better understand not only the early universe, but also galaxies closer to home.

This research has been published in the Astrophysical Journal Letters.

The Nancy Grace Roman Space Telescope is managed at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with participation by NASA's Jet Propulsion Laboratory and Caltech/IPAC in Southern California, the Space Telescope Science Institute in Baltimore, and a science team comprising scientists from various research institutions. The primary industrial partners are BAE Systems, Inc. in Boulder, Colorado; L3Harris Technologies in Melbourne, Florida; and Teledyne Scientific & Imaging in Thousand Oaks, California.

Source: Space Telescope Science Institute (STScI)/Press Releases

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About This Release

Credits:

Media Contact:

Matthew Brown
Space Telescope Science Institute, Baltimore, Maryland

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland

Science: Jane Dai (University of Hong Kong), Rudrani Kar Chowdhury (University of Hong Kong)

Permissions: Content Use Policy

Related Links and Documents

• Science Paper: Detecting Population III Stars through Tidal Disruption Events in the Era of JWST and Roman, PDF (1.44 MB)
• "Detecting Population III Stars through Tidal Disruption Events in the Era of JWST and Roman" by R. Kar Chowdhury et al.

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Radio telescope becomes stellar ‘speed camera’ in deep-space experiment

Matter spirals into a neutron star from a nearby companion, boosting the jets from the top and bottom of the neutron star as it does. Credit: ESA

In a world first, researchers have measured the jets of neutron stars to be moving at 114,000km per second – one-third the speed of light.

The international team achieved this result using the European Space Agency (ESA)’s orbiting gamma ray telescope, Integral, and the Australia Telescope Compact Array (ATCA) on Gomeroi Country which is owned and operated by Australia’s national science agency, CSIRO.

Neutron stars, like black holes, have huge gravitational pulls. When pulling matter from a nearby star, their extreme environments cause the occasional thermonuclear explosion and constant jets of matter shooting into space. Not much is known about these jets, including their composition and speed.

These latest results, published today in Nature, revealed that thermonuclear explosions – detected by Integral – pushed gas into the jets. The jets were then tracked with ATCA allowing their speed to be recorded.

Professor James Miller-Jones from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) was one of the project researchers.

He said it’s typically hard to measure the speed of a jet, but discovering the jets are enhanced after every thermonuclear explosion provides a new way of measuring their speeds.

“The explosion tells us when the enhanced jets were launched, and we simply time them as they move downstream – just like we would time a 100m sprinter as they move between the starting blocks and the finish line,” Professor Miller-Jones said.

Jet bursts on dead stars lead to surprising results from ICRAR on Vimeo

CSIRO’s Dr Jamie Stevens, who leads the ATCA operations team in Narrabri, describes the telescope as a world-class and adaptable instrument.

“Radio telescopes are extremely versatile in the research they can do,” Dr Stevens said.

“The sensitivity and stability of ATCA allowed this research team to observe rapid changes in the neutron star’s surroundings over three days.

“This new method will help astronomers to better understand jets in many different environments and the complex events that build our Universe,” he said.

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

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Publication

Russell, Degenaar, van den Eijnden et al, ‘Thermonuclear explosions on neutron stars reveal the speed of their jets’, Nature, 27 March 2024, DOI 10.1038/s41586-024-07133-5

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Mysterious object in the gap

Inspiral of a lower mass-gap black hole (dark gray surface) and a neutron star (orange sphere). The emitted gravitational waves are shown in colors from dark blue to cyan. © I. Markin (Potsdam University), T. Dietrich (Potsdam University and Max Planck Institute for Gravitational Physics), H. Pfeiffer, A. Buonanno (Max Planck Institute for Gravitational Physics)

Shortly after the start of the fourth observing run, the LIGO-Virgo-KAGRA collaborations detected a remarkable gravitational-wave signal.

The LIGO Livingston detector observed the signal, called GW230529, on May 29, 2023, from the merger of a neutron star with an unknown compact object, most likely an unusually light-weight black hole. With a mass of only a few times that of our Sun, the object falls into the “lower mass gap” between the heaviest neutron stars and the lightest black holes. Researchers at the Max Planck Institute for Gravitational Physics contributed to the discovery with accurate waveform models, new data-analysis methods, and sophisticated detector technology. Although this particular event was observed only because of its gravitational waves, it increases the expectation that more such events will also be observed with electromagnetic waves in the future.

The lower mass gap

For about 30 years, researchers have debated whether there is a mass gap separating the heaviest neutron stars from the lightest black holes. Now, for the first time, LVK scientists have found an object whose mass falls right into this gap, which was thought to be almost empty. “These are very exciting times for gravitational-wave research as we delve into realms that promise to reshape our theoretical understanding of astrophysical phenomena dominated by gravity,” says Alessandra Buonanno, Director at the Max Planck Institute for Gravitational Physics in Potsdam Science Park.

Einstein's theory of general relativity predicts neutron stars to be lighter than three times the mass of our Sun. However, the exact value of the maximum mass that a neutron star can have before collapsing into a black hole is unknown. “Considering electromagnetic observations and our present grasp of stellar evolution, there were expected to be very few black holes or neutron stars within the range of three to five solar masses. However, the mass of one of the newly discovered objects precisely aligns with this range,” Buonanno elaborates.

In recent years, astronomers have uncovered several objects whose masses potentially fit within this elusive gap. In the case of GW190814, LIGO and Virgo identified an object at the lower boundary of the mass spectrum. However, the compact object detected via the gravitational-wave signal GW230529 marks the first instance where its mass unequivocally falls within this gap.

New observing run with more sensitive detectors and improved search methods

The highly successful third observing run of the gravitational-wave detectors ended in spring 2020, bringing the number of known gravitational-wave events to 90. Before the start of the fourth observing run O4 on May 24, 2023, the LVK researchers made several improvements to the detectors to increase their sensitivity. “Researchers at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Hannover, together with LIGO colleagues, have improved the laser sources of the LIGO detectors at the heart of the instruments,” explains Karsten Danzmann, Director at AEI and Director of the Institute for Gravitational Physics at Leibniz University Hannover. “They provide high-precision laser light with an output power of up to 125 watts, with the same characteristics over very short and very long time scales.” Benno Willke, leader of the laser development group at AEI Hannover, adds: “The reliability and performance of the new solid-state laser amplifiers is amazing and I'm convinced that they will still be used in the next detector upgrade.”

But not only the hardware has been improved: the new observing run took advantage of an efficient waveform code infrastructure, and the accuracy, speed, and physical content of the waveform models developed at the AEI Potsdam were improved, so that black-hole properties can be extracted in a few days.

O4 starts with a bang

Just five days after the launch of O4, things got really exciting: on May 29, 2023, the LIGO Livingston detector observed a gravitational wave that was published within minutes as signal candidate “S230529ay”. The result of this “online analysis”, which was performed almost in real time as the signal arrived, was that a neutron star and a black hole most likely merged about 650 million light-years from Earth. However, it is not possible to say exactly where the merger took place because only one gravitational-wave detector was recording scientific data at the time of the signal. Therefore, the direction from which the gravitational waves came could not be determined.

The LVK researchers made sure that the signal was not a local disturbance in the LIGO Livingston detector, but actually came from deep space. “Among other things, we examined all the perturbations and random fluctuations of detector noise that resemble weak signals,” explains Frank Ohme, leader of a Max Planck research group at AEI Hannover. “GW230529 clearly stands out from this background and was consistently detected by several independent search methods. This clearly indicates an astrophysical origin of the signal.”

The astrophysicists also used GW230529 to test Einstein's general theory of relativity. “GW230529 is in perfect agreement with the predictions of Einstein's theory,” says Elise Sänger, a graduate student at AEI Potsdam who was involved in the study. “It provided some of the best constraints to date on alternative theories of gravity using LVK gravitational-wave events.”

GW230529: Neutron star meets unknown compact object

To determine the properties of the objects that orbited each other and merged, producing the gravitational-wave signal, astronomers compared data from the LIGO Livingston detector with two state-of-the art waveform models. “The models incorporate a range of relativistic effects to ensure the resulting signal model is as realistic and comprehensive as possible, facilitating comparison with observational data,” says Héctor Estellés Estrella, a postdoctoral researcher in the team AEI Potsdam team who developed one of the models. “Among other things, our waveform model can accurately describe black holes swirling around in space-time at a fraction of the speed of light, emitting gravitational radiation across multiple harmonics,” adds Lorenzo Pompili, a PhD student at the AEI Potsdam who also built the model.

Numerical simulation of the compact binary system GW230529: Matter and waves

© I. Markin (Potsdam University), T. Dietrich (Potsdam University and Max Planck Institute for Gravitational Physics), H. Pfeiffer, A. Buonanno (Max Planck Institute for Gravitational Physics)

GW230529 was formed by the merger of a compact object with 1.3 to 2.1 times the mass of our Sun with another compact object with 2.6 to 4.7 times the solar mass. Whether these compact objects are neutron stars or black holes cannot be determined with certainty from gravitational-wave analysis alone. However, based on all the known properties of the binary, LVK astronomers believe that the lighter object is a neutron star and the heavier is a black hole.

The mass of the heavier object therefore lies confidently in the mass gap, which was previously thought to be mostly empty. None of the previous candidates for objects in this mass range have been identified with the same certainty.

Scientists expect more observations of similar signals

Of all the neutron star-black hole mergers observed to date, GW230529 is the one in which the masses of the two objects are the least different. Tim Dietrich, a professor at the University of Potsdam and leader of a Max Planck Fellow group at the AEI, explains: “If the black hole is significantly heavier than the neutron star, no matter is left outside the black hole after the merger, and no electromagnetic radiation is emitted. Lighter black holes, on the other hand, can rip apart the neutron star with their stronger tidal forces, ejecting matter that can glow as a kilonova or a gamma-ray burst”.

The observation of such an unusual system shortly after the start of the O4 run also suggests that further observations of similar signals can be expected. The LVK researchers have calculated how often such pairs merge and found that these events occur at least as often as the previously observed mergers of neutron stars with heavier black holes. Therefore, an afterglow in the electromagnetic spectrum should be observed more frequently than previously thought.

A mysterious compact object

LVK scientists can only make an educated guess as to how the heavier of the compact objects – most likely a lightweight black hole – in the binary that emitted GW230529 was formed. It is too light to be the direct product of a supernova. It is possible – but unlikely – that it was formed during a supernova, where material initially ejected in the explosion falls back and causes the newly formed black hole to grow. It is even less likely that the black hole was formed in the merger of two neutron stars. An origin as a primordial black hole in the early days of the universe is also possible, but not very likely. Finally, the researchers cannot completely rule out the possibility that the heavier object is not a light black hole, but an extremely heavy neutron star.

The fourth observing run continues

So far, a total of 81 significant signal candidates have been identified in O4a, the first half of the fourth observing run. GW230529 is the first of these that has now been published after detailed investigation.

After a commissioning break of several weeks and a subsequent engineering run, O4b, the second half of O4, begins on April 10. Both LIGO detectors, Virgo, and GEO600, will participate in O4b.

While the observing run continues, LVK researchers are analyzing the observational data from O4a and checking the remaining 80 significant signal candidates that have already been identified. The sensitivity of the detectors should be slightly increased after the break. By the end of the fourth observing run in February 2025, a similar number of new candidates are expected to be added, and the total number of observed gravitational-wave signals will soon exceed 200.

Source: Max Planck Institute for Gravitational Physics

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Gravitational-wave observatories

LIGO is funded by the NSF, and operated by Caltech and MIT, which conceived and built the project. Financial support for the Advanced LIGO project was led by NSF with Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council) and Australia (Australian Research Council) making significant commitments and contributions to the project. More than 1,600 scientists from around the world participate in the effort through the LIGO Scientific Collaboration, which includes the GEO Collaboration. Additional partners are listed at https://my.ligo.org/census.php.

The Virgo Collaboration is currently composed of approximately 880 members from 152 institutions in 17 different (mainly European) countries. The European Gravitational Observatory (EGO) hosts the Virgo detector near Pisa in Italy, and is funded by Centre National de la Recherche Scientifique (CNRS) in France, the Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and the National Institute for Subatomic Physics (Nikhef) in the Netherlands. A list of the Virgo Collaboration groups can be found at: https://www.virgo-gw.eu/about/scientific-collaboration/. More information is available on the Virgo website at https://www.virgo-gw.eu.

KAGRA is the laser interferometer with 3 km arm-length in Kamioka, Gifu, Japan. The host institute is Institute for Cosmic Ray Research (ICRR), the University of Tokyo, and the project is co-hosted by National Astronomical Observatory of Japan (NAOJ) and High Energy Accelerator Research Organization (KEK). KAGRA collaboration is composed of over 400 members from 128 institutes in 17 countries/regions. KAGRA’s information for general audiences is at the website https://gwcenter.icrr.u-tokyo.ac.jp/en/. Resources for researchers are accessible from http://gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA.

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Media contacts:

Dr. Benjamin Knispel
Press Officer AEI Hannover
+49 511 762-19104
benjamin.knispel@aei.mpg.de

Dr. Elke Müller
Press Officer AEI Potsdam, Scientific Coordinator
+49 331 567-7303
+49 331 567-7298 (Fax)
elke.mueller@aei.mpg.de

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Scientific contacts:

Prof. Dr. Alessandra Buonanno
+49 331 567-7220
+49 331 567-7298 (Fax)
alessandra.buonanno@aei.mpg.de
Homepage of Alessandra Buonanno

Prof. Dr. Karsten Danzmann
Director | LSC Principal Investigator
+49 511 762-2356
+49 511 762-5861 (Fax)
karsten.danzmann@aei.mpg.de

Homepage of Karsten Danzmann

Dr. Frank Ohme
Research Group Leader | LSC Principal Investigator
+49 511 762-17171
+49 511 762-2784 (Fax)

frank.ohme@aei.mpg.de
Homepage of Frank Ohme

Prof. Dr. Tim Dietrich
Max Planck Fellow
+49 331 567-7253
+49 331 567-7298 (Fax)
tim.dietrich@aei.mpg.de

Dr. Héctor Estellés Estrella
Junior Scientist/Postdoc
+49 331 567-7193
hector.estelles@aei.mpg.de

Lorenzo Pompili
PhD Student
+49 331 567-7182
+49 331 567-7298 (Fax)
lorenzo.pompili@aei.mpg.de

Elise Sänger
PhD Student
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elise.saenger@aei.mpg.de

Apl. Prof. Dr. Benno Willke
Research Group Leader
+49 511 762-2360
benno.willke@aei.mpg.de

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Publication

The LIGO Scientific Collaboration, the Virgo Collaboration, and the KAGRA Collaboration
Observation of Gravitational Waves from the Coalescence of a 2.5–4.5 M_⊙
Compact Object and a Neutron Star

Source

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Further information

Current gravitational-wave astronomy Up-to-date information on gravitational-wave astronomy and expertise at the Max Planck Institute for Gravitational Physics in Hannover and Potsdam.

more

LIGO news item
about GW230529

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