Uncover the secret of 50 black hole "pairing"

Four years ago, billions of light-years away, two huge black holes merged with each other while rotating, causing short ripples in space and time, and physicists discovered gravitational waves for the first time. Since then, scientists seem to have opened new doors and discovered a series of similar events one after another.

　https://www.2021hermes.com/ -　According to a report by "Science", researchers from the Global Gravitational Wave Detector Network recently published the first statistical analysis report on the 50 similar events that have been discovered so far in the form of 4 articles on the preprint server arXiv.

　　 The report shows that black holes, the super gravitational fields left by these massive stars when they collapse, are more common and stranger than scientists expected. The researchers also uncovered some mysteries in the report, such as how these black holes “pair” before they merge.

The above observation data partly come from three large L-shaped optical instruments called interferometers, two of which belong to the Laser Interferometer Gravitational Wave Observatory (LIGO), and the third detector is the Virgo Interferometer (VIRGO) near Pisa, Italy. Joined the search for gravitational waves in 2017.

　　 The detector’s new ability to conduct a census of black holes allows researchers to detect whether a pair of black holes in the merger point in the same orbital direction as each other, which is a potential clue to how the pair of black holes originally came together.

If the spin direction is the same as the direction of the orbits surrounding each other, then the pair of black holes may be formed by a pair of co-born stars. They have naturally obtained matching spins and are still accompanied by the collapse; if the spin The direction of rotation is different from the direction of each other's orbit, then the pair of black holes may be "paired" together in some way after they were formed separately.

　　 At present, which of the above formation methods is dominant is still a topic of debate among researchers.

　　 Especially, if one of a pair of black holes rotates in the opposite direction to the orbit, the pair of black holes is more likely to come from a mixture of black holes that have formed. But Maya Fishbach, an astrophysicist at Northwestern University and a member of LIGO, said it is difficult to determine whether this has happened from a single chirp signal.

　　 Through the overall analysis of these events, the researchers sorted out at least some evidence that black hole mergers involve reverse rotation. Fishbach believes that this result in turn proves that black holes can be formed in more than one way.

　　 "We have answered many questions that we didn't even realize, but we asked more questions. This is just the beginning of science." Fishbach said.