Space brings us new analyses of stellar graveyards, which astronomers study to discover how stars develop and, eventually, die – turning into dense neutron stars or denser black holes. Using a new laser-based gravity-wave detector, they’ve found a lot more going on in one stellar graveyard, including the largest black-hole binary system yet discovered:
The newly analyzed data — collected by the gravitational wave detectors LIGO (Laser Interferometer Gravitational-Wave Observatory), Virgo and KAGRA (Kamioka Gravitational Wave Detector) — doubles the number of known “mixed mergers” between black holes and neutron stars, from 1 to 2. In total, 128 new mergers of various types were “heard” during the fourth operating run of LIGO, Virgo, and KAGRA between May 2023 and January 2024, the first nine months of its 18-month 4th operating run (O4).
“This new update really highlights the capabilities of both the international network of gravitational-wave detectors and the analysis techniques which have been developed to dig very faint signals out of the data,” team leader Daniel Williams, a researcher at the Institute for Gravitational Research (IGR) at the University of Glasgow in Scotland, said in a statement.
“What we’ve observed in the first part of the two-year-long fourth observing run has broadened our understanding of the cosmic graveyard: we’ve seen the heaviest black holes yet,” Williams added.
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“The biggest stars live the shortest lives, so they can be hard to study in other ways. Stars live their lives in many different environments. Some form in dense stellar environments like nuclear star clusters, where millions of stars are in close proximity,” [team member Christopher] Berry added. “Here, we might expect that following a binary black hole merger, the remnant black hole could find a new partner and merge again, forming an even bigger black hole.”
Berry said that, with GWTC-4.0 (Version 4.0 of the Gravitational-Wave Transient Catalog), LIGO-Virgo-KAGRA scientists have seen telltale hints that some of the sources could come from black holes that are themselves the result of previous mergers.
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“The universe is expanding, and the speed at which it is doing so is known as the Hubble Constant. A unique feature of black hole mergers is that we can tell how far away they were directly from our observation,” said team member and IGR researcher Rachel Gray. “This means that each merger we detect gives some information about the universe’s expansion rate.
“By combining this information from many mergers, we can improve our measurement of the Hubble Constant, helping to answer one of the big unanswered questions of modern astronomy: exactly how fast is the universe expanding?”