Astronomers Detect a Black Hole Merger That's So Massive It Shouldn't Exist
Today, the LIGO Collaboration announced the detection of the most colossal black hole merger known to date, the final product of which appears to be a gigantic black hole more than 225 times the mass of the Sun. Much about this signal, designated GW231123, contradicts known models for stellar evolution, sending physicists scrambling to apprehend how such a merger was even possible.
LIGO, or the Laser Interferometer Gravitational-wave Observatory, made physics history in 2015 by detecting gravitational waves for the first time, capturing the cosmological echo of two colliding black holes. Since its Nobel-winning discovery, the LIGO Collaboration, an international partnership between LIGO and Virgo and KAGRA in Italy and Japan, respectively, has continued its meticulous surveillance of the galaxy. The collaboration has detected numerous signals from neutron stars, supernovas, and some 300 black hole mergers.
But GW231123, first observed on November 23, 2023, seems to be an unprecedented beast of a black hole merger. Two enormous black holes—137 and 103 times the mass of the Sun—managed to keep it together despite their immense combined mass, spinning at 400,000 times the speed of Earth's rotation to form an ever bigger black hole. To put its size into perspective, the previous record holder for such a merger, GW190521, is roughly 140 times the mass of the Sun.
Considering the gravitationally chaotic nature of black hole environments, with their pushes and pulls, it's remarkable that this merger was stable enough for the resulting gravitational waves to reach LIGO, which detected the signals for a duration of 0.1 seconds. Such episodes should be 'forbidden' according to standard evolution models, said Mark Hannam, LIGO member and physicist at Cardiff University, in a statement.
'One possibility is that the two black holes in this binary formed through earlier mergers of smaller black holes,' he surmised. 'This is the most massive black hole binary we've observed through gravitational waves, and it presents a real challenge to our understanding of black hole formation.'
'The black holes appear to be spinning very rapidly—near the limit allowed by Einstein's theory of general relativity,' explained Charlie Hoy, LIGO member and physicist at the University of Portsmouth in England, in the same release. 'That makes the signal difficult to model and interpret. It's an excellent case study for pushing forward the development of our theoretical tools.'
Scientists will present their findings about GW231123 next week at the 24th International Conference on General Relativity and Gravitation (GR24) and the 16th Edoardo Amaldi Conference on Gravitational Waves, held jointly as the GR-Amaldi meeting in Glasgow, U.K. Following that, the data will be out for public scrutiny, kicking off the race to unravel GW231123's mystery—though it's unlikely we'll have a clear answer any time soon.
'It will take years for the community to fully unravel this intricate signal pattern and all its implications,' added Gregorio Carullo, also a LIGO member and physicist at the University of Birmingham, England. 'Despite the most likely explanation remaining a black hole merger, more complex scenarios could be the key to deciphering its unexpected features. Exciting times ahead!'
Physicists first conceived of gravitational waves as early as the late 19th century, but the idea gained popular momentum thanks to Albert Einstein. As one of the few observational methods that doesn't need light to 'see' cosmic phenomena, gravitational waves are unmatched in their potential for helping humanity uncover the many mysteries of black holes, ancient stars, and even dark matter. So, indeed—exciting times ahead!
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In a 2021 paper on ethical considerations for diagnosis and care, an AAN committee said that biomarker testing could be clinically useful for some symptomatic patients, but testing asymptomatic individuals is 'recommended solely in a research setting' because of potential harms 'and the absence of interventions capable of favorably altering the natural history of the disease.' Eric Topol, MD, chair of the Department of Translational Medicine at Scripps Research in La Jolla, California, is bullish on the potential for blood-based biomarker tests. In a blog post, he called the pTau-217 biomarker 'one of the most exciting advances in neurology for decades, giving us a new opportunity to accurately predict and potentially prevent (or at least substantially delay) mild cognitive impairment and Alzheimer's.' But, wrote Topol, who is the former editor in chief of MedscapeMedical News , 'I don't think these biomarkers are going to be useful in people at low risk.' 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DTC companies tell buyers that results could motivate them to change their lifestyle to reduce their future risk for AD and dementia. But some participants in Mozersky's study said they didn't want to know their status because there were no preventive treatments. Test results weren't seen as 'actionable,' she said. Some studies have shown a degree of fatalism in individuals after receiving a test result, whether it's positive or negative. A group of Israeli researchers studied responses of people given PET scans to detect beta-amyloid. Before testing, all participants said they were motivated to adopt lifestyle changes to fight dementia. However, after testing, both those who had elevated beta-amyloid and those who did not reported a much lower desire to change their lifestyle. Those with normal scans probably felt relieved, wrote the researchers. The group with abnormal scans was too small to fully understand their reaction, they wrote. Concerns about insurance coverage might also deter potential test-takers. Overall, 44% of those responding to the Alzheimer's Association survey said they were worried that insurers might not cover healthcare costs in the future if they had received a positive test earlier. Respondents also worried about test accuracy, the cost of testing, and whether a positive test might lead to a prohibition on some activities, like driving. What About the Doctors? The DTC companies promise buyers that results will be private and won't be shared with insurers — or with clinicians. And that raises another issue for many who are concerned about the lack of a physician intermediary with at-home testing. 'You remove the opportunity for clinicians to both review the result and figure out how to interpret it before it's communicated to the patient,' Jalayne J. Arias, JD, a bioethicist and associate professor of Health Policy and Behavioral Sciences at Georgia State University, Atlanta, told Medscape Medical News . Many in the field have been 'thinking really carefully about how do we provide guidance to clinicians about biomarker testing,' she said. 'Those issues are just heightened when we put it into a direct-to-consumer model,' Arias said. Arias — who with colleagues published an analysis of potential insurance issues with biomarker tests in JAMA Neurology — said that prohibitions against discrimination based on preexisting conditions means that most likely, health insurers could not use testing data to deny coverage or increase premiums. But, she said, 'there are some question marks around the discrimination risks.' This is especially true for people seeking long-term care, disability or life insurance, she added. If a test result is not documented in a medical record, it's not clear whether the individual has an obligation to disclose the result to an insurer, said Arias. Given all the unanswered questions about how results should be interpreted, to whom the results should be disclosed, and when and how to have discussions with patients, 'it's hard for me to imagine that we're quite ready for a direct-to-consumer' test, Arias said. Mozersky noted that Washington University has a financial stake in C2N Diagnostics, which makes the PrecivityAD — biomarker tests for AD. Arias reported having no conflicts of interest.
