Details of black hole rotation revealed using new method

(ORDO NEWS) — Researchers from Cornell University, USA, for the first time were able to detect, by analyzing gravitational wave data, possible signs of resonances between the orbital and proper rotation of black holes that are part of binary systems.

This was a step forward towards a deeper understanding of the mechanisms of supernovae and other major problems of modern astrophysics.

“These resonances were predicted over a decade ago based on Einstein’s general theory of relativity,” said astrophysicist Vijay Varma. “We have found the first ‘hints’ of resonances in gravitational wave data collected by the LIGO (Laser Interferometer Gravitational-Wave Observatory) and Virgo observatories.”

The rate of rotation of a black hole tells about the history of its formation. As Varma said, for black holes that form a pair, the directions of each black hole’s own rotation carry valuable information, especially if you analyze their position in relation to each other.

In a new study, Varma and colleagues report that the directions of the angular momentum of two black holes projected onto the orbital plane turn out to be anti-parallel, which may indicate a resonance between their own rotational and orbital motion. Additional observations are needed to confirm these trends, Varma said.

Black holes usually rotate on their own axis, since they are formed from spinning stars. When two such black holes rotate relative to each other as part of a binary system, there is an interaction between their own rotation and orbital motion.

Binary black holes lose energy by emitting gravitational waves, so over time they move closer and merge. The momentum of some black holes is oriented along or against the direction of the orbital angular momentum, resulting in a “boring” union in a fixed plane.

But other black holes may have angular momenta of their own rotation that are tilted with respect to the orbital angular momentum vector, resulting in an interaction between these angular momentum that causes precession.

Resonances between intrinsic and orbital rotation can occur in precessing binary systems, but this depends on the type of supernova explosion mechanism that produces a black hole from the progenitor star.

If the supernova radiation is not symmetrical in all directions, then the black hole at birth receives an impulse similar to the recoil acting on a gun when fired.

“If the ‘recoil’ of the supernova is large enough, then the binary system can enter into resonance between its own and orbital rotation,” Varma said. “These are special configurations in which the projections of the direction of the angular momentum vectors in the orbital plane are either parallel or anti-parallel.”

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