The Universe Is Full of ‘Impossible’ Black Holes. Now Scientists Know Why | WIREDSkip to main contentMenuSECURITYPOLITICSTHE BIG STORYBUSINESSSCIENCECULTUREREVIEWSMenuAccountAccountNewslettersSecurityPoliticsThe Big StoryBusinessScienceCultureReviewsChevronMoreExpandThe Big InterviewMagazineEventsWIRED InsiderWIRED ConsultingNewslettersPodcastsVideoLivestreamsMerchSearchSearchJorge GarayScienceMay 24, 2026 4:00 AMThe Universe Is Full of ‘Impossible’ Black Holes. Scientists Now Know WhyThere are black holes that are too big to be born from the death of a star but aren’t quite supermassive either. There’s finally evidence for where those came from.Illustration: NASACommentLoaderSave StorySave this storyCommentLoaderSave StorySave this storyAn international team of astrophysicists has found evidence that the universe recycles black holes, merging them to form even larger ones. Gravitational waves recorded in recent years show that some of the heaviest black holes within star clusters exhibit clear signs of being “second-generation” black holes—products of past collisions—and therefore could not have originated from the collapse of a massive star.Impossible Black HolesThe evolutionary theory of stars explains that, at the end of the lives of the most massive stars, their cores compress until they form a point so dense that it curves space-time to infinity. This is the classic black hole, with masses 10 to 40 times that of the sun. There are also supermassive black holes, in the center of galaxies, with millions or billions of solar masses, whose origin is related to processes that occurred in the earliest moments of the universe.Between these two extremes lies a contested category: black holes with masses between 40 and 100 solar masses. They are too heavy to be born after the death of a star, but they do not reach the necessary dimensions to emerge from the collapse of a gigantic cloud of matter. Conventional stellar physics considers them “impossible,” yet they appear frequently in detections.A "normal" sized black hole, isolated in space.
Courtesy of Space Telescope Science Institute Office of Public OutreachAstrophysicists propose that these massive black holes could form by the merging of two or more smaller, ultradense objects. The idea was plausible, but it needed evidence. Until relatively recently, there was no way to obtain it.Then gravitational wave detectors came on the scene. These instruments use lasers to measure the micro-distortion of space-time generated by the collision of extremely dense objects. The first detection, in 2015, confirmed a merger between black holes. Since then, each new signal has allowed for a better characterization of these structures and revealed that these collisions occur much more frequently than previously imagined.The Second-Generation SignatureThe study, published this month in Nature Astronomy, analyzed a transient catalog of gravitational waves generated by the world's three leading observatories. The database included 153 reliable detections of black hole mergers. Among them, 34 corresponded to particularly heavy objects.By comparing all the signals, the team identified two distinct populations. The lighter black holes, up to about 40 solar masses, showed small, aligned spins, as expected for objects born from the collapse of a star. But from a certain point, around 45 solar masses, a completely different population appeared: heavier black holes, spinning rapidly and in chaotic directions—a statistical signature that can arise only when the object has already participated in a previous merger.“This is the exact signature you would expect if black holes repeatedly merged into dense stellar clusters,” said Isobel M. Romero-Shaw, coauthor of the research, in a statement from Cardiff University.So far researchers have not directly observed any of these “impossible” black holes. They do not appear in x-rays or in the visible spectrum, unlike supermassive ones. However, their collisions vibrate space-time, and that vibration reveals masses that stellar physics cannot explain.This study shows that the heaviest black holes are built rather than born. They arise from previous generations of collisions, assembled in the densest environments in the cosmos.This story originally appeared in WIRED en Español and has been translated from Spanish.CommentsBack to topTriangleYou Might Also LikeHow to find us: Add WIRED.com to your preferred sources in GoogleThese women are trying to optimize their vaginasBig Story: AI gig work is the new waiting tables—and it's soul-crushingThis summer, the American water crisis becomes realEvent: How to adapt, compete, and win in the next era of businessJorge Garay is a contributor to WIRED en Español. He specializes in technology, cybersecurity, and the legislative impact of social media. He has worked in digital media for 10 years. 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An international team of astrophysicists has found evidence suggesting that the universe recycles black holes through mergers, leading to the formation of even larger ones. This research addresses the existence of black holes that present theoretical difficulties within conventional stellar physics, specifically those with masses between forty and one hundred solar masses. These objects are considered "impossible" because they are too heavy to be formed from the collapse of a single massive star, yet they do not possess the required dimensions to emerge from the complete gravitational collapse of a gigantic cloud of matter.

The text posits that these massive black holes likely form through the merging of two or more smaller, ultradense objects, an idea that required empirical evidence to validate. The advent of gravitational wave detectors provided this necessary evidence. These instruments measure the micro-distortion of space-time generated by the collision of extremely dense objects. Since the first detection of a black hole merger in 2015, subsequent signals have allowed researchers to better characterize these structures and indicate that such collisions occur far more frequently than previously hypothesized.

A study published in Nature Astronomy analyzed a catalog of gravitational waves from numerous black hole mergers to identify distinct populations. The lighter black holes, up to approximately forty solar masses, exhibited aligned spins, consistent with the expected outcome of objects born from stellar core collapse. However, beyond a certain mass threshold, around forty-five solar masses, a different population emerged: these heavier black holes were observed spinning rapidly and in chaotic directions. This statistical signature is consistent with the expectation that these objects have participated in multiple previous mergers within dense stellar clusters.

The research suggests that the heaviest black holes are not born directly but are instead built up through successive collisions, assembling within the densest regions of the cosmos. Although these "impossible" black holes are not directly observed in the visible or x-ray spectra, their interactions cause vibrations in space-time that reveal masses inconsistent with standard stellar physics. Therefore, the findings demonstrate that the heaviest black holes arise from the accumulated history of past collisions, reflecting processes that occurred in the universe's densest environments.