Signals buried deep inside gravitational wave observatory data suggest a collision between two black holes that were certainly created in separate locations.
Almost all of the spacetime ripples observed by experiments such as the Laser Interferometer Gravitational-Wave Observatory, or LIGO, originate from collisions between black holes and neutron stars that are likely related (SN: 1/21/2). They were originally pairs of stars that were created at the same time and location, later collapsing to become circling black holes or neutron stars.
According to existing data from LIGO in the United States and its sister observatory Virgo in Italy, a recently observed marriage of black holes appears to be of an unconnected couple. According to a publication forthcoming in Physical Review D, this is supported by the way in which they were spinning when they merged into one. As they orbit each other, black holes born in the same location tend to have their spins aligned, like two toy tops spinning on a table. The absence of a link between the spins and orbits of this pair suggests that they were born in different locations.
Seth Olsen, a physicist at Princeton University, explains, “This tells us that we’ve finally discovered a pair of black holes that must have originated from a non-grow-old-together channel.”
Observations of gravitational waves have revealed back holes merging that are not precisely aligned, but the majority are close enough to strongly suggest familial ties. The latest finding, which Olsen and colleagues discovered by trawling through data made available by the LIGO-Virgo partnership, is distinct. One of the black holes is effectively rotating in the opposite direction.
This is unlikely unless the two black holes originate from independent locations. They likely met late in their stellar lifetimes, as opposed to the black hole littermates that appear to account for the majority of gravitational wave observations. In addition to the merger of two independent black holes, Olsen and his colleagues discovered nine more black hole mergers that had been missed by previous LIGO-Virgo studies (SN: 8/4/21).
Patrick Brady, a physicist from the University of Wisconsin–Milwaukee unaffiliated with the new study and a spokesperson for the LIGO scientific partnership, explains, “This is the beautiful thing about this type of analysis.” “We provide the data in a format that can be utilized by others, so that [they] can experiment with different ways.”
In order to identify so many new signals in data that had already been analyzed by other scientists, Olsen’s team reduced the analytical hurdle slightly.
“Of the ten new ones,” Olsen says, “approximately three of them are statistically likely due to noise” rather than confirmed detections of black hole mergers. Assuming that the merging of unrelated black holes is not among the incorrect signals, it almost probably reveals a black hole history distinct from those previously observed.
Olsen states, “It would be [very] difficult for this to originate from two black holes that have spent their entire existence together.” “This was likely a capture. It’s fantastic that we can now begin exploring that portion of the [black hole] population.”
Brady notes that “we do not understand the theory [of black hole mergers] well enough to predict all of these types of events with certainty.” However, the newest research may indicate the existence of new and intriguing potential in gravitational wave astronomy. “Let’s investigate this clue to determine whether it truly reflects something uncommon,” he suggests. Otherwise, we’ll study other stuff.