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Recent Observations Challenge our Understanding of Giant Black Holes
Black holes are among the most mysterious and powerful objects in the Universe. These behemoths form when sufficiently massive stars reach the end of their life cycle and experience gravitational collapse, shedding their outer layers in a supernova. Their existence was illustrated by the work of German astronomer Karl Schwarzschild and Indian-American physicist Subrahmanyan Chandrasekhar as a consequence of Einstein’s Theory of General Relativity. By the 1970s, astronomers confirmed that supermassive black holes (SMBHs) reside at the center of massive galaxies and play a vital role in their evolution.
However, only in recent years were the first images of black holes acquired by the Event Horizon Telescope (EHT). These and other observations have revealed things about black holes that have challenged preconceived notions. In a recent study led by a team from MIT, astronomers observed oscillations that suggested an SMBH in a neighboring galaxy was consuming a white dwarf. But instead of pulling it apart, as astronomical models predict, their observations suggest the white dwarf was slowing down as it descended into the black hole – something astronomers have never seen before!
The study was led by Megan Masterson, a PhD student from the MIT Kavli Institute for Astrophysics and Space Research. She was joined by researchers from the Nucleo de Astronomia de la Facultad de Ingenieria, the Kavli Institute for Astronomy and Astrophysics (KIAA-PU), the Center for Space Science and Technology (CSST), and the Joint Space-Science Institute at the University of Maryland Baltimore County (UMBC), the Centro de Astrobiologia (CAB), the Cahill Center for Astronomy and Astrophysics, the Harvard & Smithsonian Center for Astrophysics (CfA), NASA’s Goddard Space Flight Center, and multiple universities.
From what astronomers have learned about black holes, these gravitational behemoths are surrounded by infalling matter (gas, dust, and even light) that form swirling, bright disks. This material and energy is accelerated to near the speed of light, causing it to release heat and radiation (mostly in the ultraviolet) as it slowly accretes onto the black hole’s “face.” These UV rays interact with a cloud of electrically charged plasma (the corona) surrounding the black hole, which boosts the rays’ into the X-ray wavelength.
Since 2011, NASA’s XMM-Newton has been observing 1ES 1927+654, a galaxy located 236 million light-years away in the constellation Draco with a black hole of 1.4 million Solar masses Suns at its center. In 2018, the X-ray corona mysteriously disappeared, followed by a radio outburst and a rise in its X-ray output—what is known as Quasi-periodic oscillations (QPO). UMBC associate professor Eileen Meyer, a co-author of this latest study, also recently released a paper describing these radio outbursts.
“In 2018, the black hole began changing its properties right before our eyes, with a major optical, ultraviolet, and X-ray outburst,” she said in a NASA press release. “Many teams have been keeping a close eye on it ever since.” Meyer presented her team’s findings at the 245th meeting of the American Astronomical Society (AAS), which took place from January 12th to 16th, 2025, in National Harbor, Maryland. By 2021, the corona reappeared, and the black hole seemed to return to its normal state for about a year.
However, from February to May 2024, radio data revealed what appeared to be jets of ionized gas extending for about half a light-year from either side of the SMBH. “The launch of a black hole jet has never been observed before in real time,” Meyer noted. “We think the outflow began earlier, when the X-rays increased prior to the radio flare, and the jet was screened from our view by hot gas until it broke out early last year.” A related paper about the jet co-authored by Meyer and Masterson was also presented at the 245th AAS.
Artist’s impression of the ESA’s XMM-Newton mission in space. Credit: ESA-C. Carreau
In addition, observations gathered in April 2023 showed a months-long increase in low-energy X-rays, which indicated a strong and unexpected radio flare was underway. Intense observations were mounted in response by the Very Long Baseline Array (VLBA) and other facilities, including XMM-Newton. Thanks to the XMM-Newton observations, Masterson found that the black hole exhibited extremely rapid X-ray variations of 10% between July 2022 and March 2024. These oscillations are typically very hard to detect around SMBHs, suggesting that a massive object was rapidly orbiting the SMBH and slowly being consumed.
“One way to produce these oscillations is with an object orbiting within the black hole’s accretion disk. In this scenario, each rise and fall of the X-rays represents one orbital cycle,” Masterson said. Additional calculations also showed that the object is probably a white dwarf of about 0.1 solar masses orbiting at a velocity of about 333 million km/h (207 million mph). Ordinarily, astronomers would expect the orbital period to shorten, producing gravitational waves (GWs) that drain the object’s orbital energy and bring it closer to the black hole’s outer boundary (the event horizon).
However, the same observations conducted between 2022 and 2024 showed the fluctuation period dropped from 18 minutes to 7, and the velocity increased to half the speed of light (540 million km/h; 360 million mph). Then, something truly odd and unexpected followed: the oscillations stabilized. As Masterson explained:
“We were shocked by this at first. But we realized that as the object moved closer to the black hole, its strong gravitational pull could begin to strip matter from the companion. This mass loss could offset the energy removed by gravitational waves, halting the companion’s inward motion.”
Artist’s impression of two neutron stars at the point at which they merge and explode as a kilonova. Credit: University of Warwick/Mark Garlick
This theory is consistent with what astronomers have observed with white dwarf binaries spiraling toward each other and destined to merge. As they got closer to each other, instead of remaining intact, one would begin to pull matter off the other, which slowed down the approach of the two objects. While this could be the case here, there is no established theory for explaining what Masterson, Meyer, and their colleagues observed. However, their model makes a key prediction that could be tested when the ESA’s Laser Interferometer Space Antenna (LISA) launches in the 2030s.
“We predict that if there is a white dwarf in orbit around this supermassive black hole, LISA should see it,” says Megan. The preprint of Masterson and her team’s paper recently appeared online and will be published in Nature on February 15th, 2025.
Further Reading: ESA, NASA, arXiv, AJL
The post Recent Observations Challenge our Understanding of Giant Black Holes appeared first on Universe Today.
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