Oval orbit casts new light on black hole - neutron star mergers

Artist’s impression of an eccentric neutron star–black hole binary
© Geraint Pratten, Royal Society University Research Fellow, University of Birmingham

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Breakthrough discovery provides new clues about how these celestial bodies - that push the known laws of physics to their limits - find each other.

Scientists have uncovered the first robust evidence of a black hole and neutron star crashing together but orbiting in an oval path rather than a perfect circle just before they merged. This discovery challenges long-standing assumptions about how these cosmic pairs form and evolve.

Researchers from the University of Birmingham, Universidad Autónoma de Madrid, and Max Planck Institute for Gravitational Physics published their findings in The Astrophysical Journal Letters.

Most neutron star-black hole pairs are expected to adopt circular orbits long before merging. But the analysis of the gravitational-wave event GW200105 shows that this system travelled on an oval orbit long before merging to form a black hole 13 times more massive than the Sun. An oval orbit is something never seen before in this kind of collision.

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"This discovery gives us vital new clues about how these extreme objects come together. It tells us that our theoretical models are incomplete and raises fresh questions about where in the universe such systems are born."

Dr Patricia Schmidt
Associate Professor

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Dr Patricia Schmidt, from the University of Birmingham, said: “This discovery gives us vital new clues about how these extreme objects come together. It tells us that our theoretical models are incomplete and raises fresh questions about where in the universe such systems are born.”

The researchers analysed data from LIGO and Virgo detectors using a new gravitational‑wave model developed at the University of Birmingham’s Institute of Gravitational Wave Astronomy. This allowed them to measure both how ‘oval’ the orbit was (eccentricity) and any spin‑induced wobbling (precession). This is the first time these two effects have been measured together in a neutron star–black hole event.

Geraint Pratten, a Royal Society University Research Fellow from the University of Birmingham, said: “The orbit gives the game away. Its elliptical shape just before merger shows this system did not evolve quietly in isolation but was almost certainly shaped by gravitational interactions with other stars, or a third companion.”

A Bayesian analysis comparing thousands of theoretical predictions to the real data, showed that a circular orbit is extremely unlikely, ruling it out with 99.5% confidence.

Black hole mass

Past analyses of GW200105, which assumed a circular orbit, underestimated the black hole mass and overestimated the neutron star mass. The new study corrects these values and finds no compelling evidence of precession, indicating that the eccentricity was imprinted by its formation rather than by spins.

Gonzalo Morras, from the Universidad Autónoma de Madrid and the Max Planck Institute for Gravitational Physics, said: “This is convincing proof that not all neutron star–black hole pairs share the same origin. The eccentric orbit suggests a birthplace in an environment where many stars interact gravitationally.”

This discovery challenges the prevailing view that all neutron star–black hole mergers arise from a single dominant formation channel and highlights the need for more advanced waveform models capable of capturing the full complexity of these systems.

The study helps to explain the growing diversity seen in compact-binary mergers and opens the door to identifying even more unusual pathways as the number of gravitational-wave detections continues to grow.

Source: University of Birmingham/News

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Notes for editors

For more information, please contact the press office on +44 (0) 121 414 2772

‘Orbital eccentricity in a neutron star – black hole merger’ - Gonzalo Morras, Geraint Pratten, and Patricia Schmidt is published by The Astrophysical Journal Letters.

As well as being ranked among the world’s top 100 institutions, the University of Birmingham is the most targeted UK university by top graduate employers. Its work brings people from across the world to Birmingham, including researchers, educators and more than 40,000 students from over 150 countries.

About the Max Planck Institute for Gravitational Physics

The Max Planck Institute for Gravitational Physics (Albert Einstein Institute) based in Potsdam and Hannover, Germany, is a leading international research centre. The research program covers the entire spectrum of gravitational physics: from the giant dimensions of the Universe to the tiny scales of strings. The unification of all these important research branches under one roof is unique in the world.

About Universidad Autónoma de Madrid

Universidad Autónoma de Madrid (UAM) is a public university with an outstanding international reputation for its high-quality teaching and research. Founded in 1968, it is recognized as one of the best Spanish universities in both national and international rankings. UAM has 8 Faculties/Schools -Science, Economics and Business Studies, Law, Arts and Humanities, Medicine, Psychology, Teachers Training and Education and a School of Engineering, and several affiliated centres, offering a wide range of studies in humanities and scientific and technical fields. Currently it has about 30,000 students, 2,800 professors and researchers and nearly 1,000 administrative staff.

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Gravitational-wave observatories release new catalog of detections

Binary Black Hole Merger

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When the densest objects in the universe collide and merge, the violence sets off gravitational waves that reverberate across space and time over hundreds of millions and even billions of years. By the time they pass through Earth, such cosmic ripples are barely discernible.

Thanks to a global network of gravitational-wave observatories—the US-based National Science Foundation-funded Laser Interferometer Gravitational-wave Observatory (LIGO), the Virgo interferometer in Italy, and the Kamioka Gravitational Wave Detector (KAGRA) in Japan—scientists can "listen" for faint wobbles in the gravitational field that could have come from far-off astrophysical smashups.

Now, the LIGO–Virgo–KAGRA (LVK) Collaboration is publishing its fourth major update to a catalog of detections since gravitational waves were first observed by LIGO in 2015. The latest findings, published in Astrophysical Journal Letters, indicate that the universe is echoing all over with a kaleidoscope of cosmic collisions

"Each new gravitational-wave detection allows us to unlock another piece of the universe's puzzle in ways we couldn't just a decade ago," says Lucy Thomas, who led part of the analysis of the catalog and is a postdoc in the Caltech LIGO lab.

The LVK's Gravitational-wave Transient Catalog-4.0 (GWTC-4) comprises detections of gravitational waves from a portion of the observatories' fourth and most recent observing run. The observatories detected 128 new gravitational-wave events, meaning signals that are likely from exotic, far-off astrophysical sources. This newest crop more than doubles the size of the gravitational-wave catalog, which previously contained 90 events compiled from all three previous observing runs.

"The GWTC-4 catalog is a real benchmark for gravitational-wave astronomy," says David Reitze, the executive director of LIGO and a research professor at Caltech. "The abundance of black holes that LIGO and its partners have detected is beginning to have a real impact on our understanding of stellar evolution and black hole formation."

The merger of a pair of black holes was the source of the very first gravitational-wave detection and colliding black holes are the source of most of the gravitational waves detected since then. In addition to the black hole binaries, the updated catalog includes the heaviest black hole binary, a binary with black holes having asymmetric masses, and a binary where both black holes have exceptionally high spins. The catalog also holds two examples of black hole–neutron star mergers.

"The message from this catalog is: We are expanding into new parts of what we call 'parameter space' and a whole new variety of black holes," says paper co-author Daniel Williams, a research fellow at the University of Glasgow and a member of the LVK Collaboration. "We are really pushing the edges and are seeing things that are more massive, spinning faster, and are more astrophysically interesting and unusual."

Among the more unusual signals that LIGO detected in the first phase of the fourth observing run was an event called GW231123_135430. As previously reported, it is the heaviest black hole binary detected to date. Scientists estimate that the signal arose from the collision of two heavier-than-normal black holes, each roughly 130 times as massive as the Sun.

Another standout is GW231028_153006, which is a black hole binary with the highest recorded inspiral spin: Both black holes appear to be spinning at about 40 percent the speed of light. "This dataset has increased our belief that black holes that collided earlier in the history of the universe could more easily have had larger spins than the ones that collided later," says LVK member Salvatore Vitale, associate professor of physics at MIT and member of the MIT LIGO Lab.

The new detections have also allowed scientists to test Albert Einstein's general theory of relativity, which describes gravity as a geometric property of space and time, using an event called GW230814_230901, which is one of the "loudest" gravitational-wave signals observed to date. The surprisingly clear signal pushed the limits of scientists' tests of general relativity, passing most with flying colors.

In addition, the updated catalog is helping scientists to nail down a key mystery in cosmology: How fast is the universe expanding today? "It's incredibly exciting to think about what astrophysical mysteries and surprises we can uncover with future observing runs," Thomas says.

"Black holes are one of the most iconic and mind-bending predictions of general relativity," says co-author and LVK member Aaron Zimmerman (PhD '13), associate professor of physics at the University of Texas at Austin, adding that when black holes collide, they "shake up space and time more intensely than almost any other process we can imagine observing. When testing our physical theories, it's good to look at the most extreme situations we can, since this is where our theories are most likely to break down, and where we have the best chance of discovery."

Read the full version of this story from the LVK Collaboration.

The paper is titled "GWTC-4.0: An Introduction to Version 4.0 of the Gravitational-Wave Transient Catalog." LIGO is funded by the NSF and is 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 UK (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 studies describing the GWTC-4.0 methods and results are online.

Source: Caltech/News

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Contact:

Whitney Clavin
(626) 395‑1944
wclavin@caltech.edu

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Related Links

LIGO Lab website

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Unusual Light Signal Hints at Distant Black Hole Merger

An artist's conception of a black hole binary in a heart of a quasar, with the data showing the periodic variability superposed. Credit: Santiago Lombeyda, Center for Data-Driven Discovery, Caltech. › Larger image

The central regions of many glittering galaxies, our own Milky Way included, harbor cores of impenetrable darkness -- black holes with masses equivalent to millions, or even billions, of suns. What's more, these supermassive black holes and their host galaxies appear to develop together, or "co-evolve." Theory predicts that as galaxies collide and merge, growing ever more massive, so too do their dark hearts.

Black holes by themselves are impossible to see, but their gravity can pull in surrounding gas to form a swirling band of glowing material called an accretion disk. When this process happens to a supermassive black hole, the result is a "quasar" -- an extremely luminous object that outshines all of the stars in its host galaxy, visible from across the universe. 

"Quasars are valuable probes of the evolution of galaxies and their central black holes," said S. George Djorgovski, professor of astronomy at the California Institute of Technology in Pasadena. "If we can systematically study a large population of quasars, we can discover rare and unusual phenomena that can help us better understand the overall picture of their evolution."

In the Jan. 7 issue of the journal Nature, Djorgovski and his collaborators, including Daniel Stern of NASA's Jet Propulsion Laboratory in Pasadena, California, report on an unusual repeating light signal from a distant quasar that they say is most likely the result of two supermassive black holes in the final stages of a merger -- something that is predicted from theory but which has never been observed before. The findings could lead to a better understanding of black hole mergers and galaxy evolution, and also help shed light on a long-standing conundrum in astrophysics called the "final parsec problem." That refers to the failure of theoretical models to predict what the final stages of a black hole merger look like, or even how long the process might take. 

"Until now, the only known examples of supermassive black holes on their way to a merger have been separated by tens or hundreds of thousands of light-years," said Stern. "At such vast distances it would take many millions, or even billions, of years for a collision and merger to occur. In contrast, these black holes are at most a few hundredths of a light-year apart, and could merge in about a million years or less."

Read the full Caltech story online:  https://www.caltech.edu/news/unusual-light-signal-yields-clues-about-elusive-black-hole-merger-45188

Caltech manages JPL for NASA.

Media Contact

Whitney Clavin
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-4673
whitney.clavin@jpl.nasa.gov 

 

Source:  JPL-Caltech