Research conducted at Cornell University has used gravitational-wave data to uncover the first possible signs of spin-orbit resonances in binary black holes, a step towards understanding the mechanisms of supernovas and other big questions in astrophysics.
“These resonances were predicted over a decade ago using Einstein’s general theory of relativity,” said astrophysicist Vijay Varma. A former Klarman Postdoctoral Fellow at the College of Arts & Sciences (A&S), Varma analyzes gravitational waves detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) and the Virgo gravitational-wave detector to learn more about binary black holes. “We find the first ‘hints’ to the resonances in gravitational-wave data from LIGO and Virgo.”
The speed at which a black hole spins reveals a lot about its history, Varma said: for black holes arranged in an interactive pair called a binary system, the direction of each black hole rotation is also revealing, especially in relation to each other.
In „Hints of Spin-Orbit Resonances in the Binary Black Hole Population“, veröffentlicht am 19. Januar Physical Verification Letters, Varma and co-workers report that the spins of the two black holes, when projected onto the orbital plane, tend to be antiparallel to each other, which may be a signature of spin.Orbit resonances. More observations are needed to confirm these trends, Varma said.
Varma conducted much of this research as a Klarman Fellow; Today he is a Marie Curie fellow at the Max Planck Institute for Gravitational Physics. Contributors to this work include Syliva Biscoveanu, Maximiliano Isi, and Salvatore Vitale from the Massachusetts Institute of Technology, and Will Farr from the Flatiron Institute.
“Resonance effects are ubiquitous in physical systems. They occur when two processes in a system occur at specifically related frequencies,” said Saul Teukolsky, Hans A. Bethe Professor of Physics (A&S), Varma’s mentor at the Cornell faculty. “In the black hole systems that Vijay studies, resonance is predicted to occur between the spin motion of the black holes and their orbit, leaving an impression on the gravitational waves produced. This work shows that if we skillfully analyze the data, we are much closer to testing this general relativity prediction than we thought.”
Black holes usually spin because they form from dying stars that spin themselves, Varma said. When two such black holes orbit each other in a binary, their spins interact with the orbit.
Binary black holes lose energy Gravitationswellen, causing the black holes to move toward each other and eventually merge, Varma said. Some binary black hole spins are aligned along or opposite to the orbital angular momentum, resulting in a “mild” merger on a fixed level. But other binary black holes have spins tilted with respect to orbital angular momentum, triggering a complicated interaction called precession.
“When the spins are tilted with respect to the orbital angular momentum, the orbit precesses like a top spinning along a tilted axis,” Varma said.
Spin-orbit resonances can occur in precessing binaries, but this depends on the nature of the supernova mechanism that spawns the black holes from their stellar progenitors, Varma said. Unless the supernova emission is symmetrical in all directions, the black hole at birth acquires a recoil velocity similar to the recoil of a fired gun.
“If the supernova recoils are large enough, the binary can end up in a spin-orbit resonance,” Varma said. “These are special configurations in which the spin directions in the orbital plane are either parallel or antiparallel.”
It was thought that the LIGO and Virgo gravitational-wave detectors were not sensitive enough to capture evidence of spin-orbit resonances. However, Varma and his collaborators used two data collection hacks to spot these early clues.
First, Varma applied computer models based on black hole simulations.
“Vijay is a global expert in developing so-called ‘surrogate models,'” Teukolsky said in a 2020 interview.
Varma said: “These models accurately capture the effect of the spins from numerical simulations. They allow us to extract as much of this information as possible from gravitational-wave observations.”
Second, the researchers learned to measure the spins just before black holes merge instead of the usual practice of measuring spins in many orbits before the merger. This late spin measurement method is the subject of a companion paper, “Measuring binary black hole orbital-plane spin direction,” published on January 19 Physical Check D.
“We’re starting to study spin-orbit resonances, which we initially thought would be impossible until next-generation detectors arrive in the 2030s,” Varma said. “Our hope is that we study these spin orbits resonances, we can learn more about the mechanism of the supernova, which has remained an enduring mystery.”
Vijay Varma et al, Hints of Spin-Orbit Resonances in the Binary Black Hole Population, Physical Verification Letters (2022). DOI: 10.1103/PhysRevLett.128.031101
Vijay Varma et al., Measuring Spin Orientations of Binary Black Holes in the Orbital Plane, Physical Check D (2022). DOI: 10.1103/PhysRevD.105.024045
Quote: Spin Behavior of Binary Black Holes Revealed Using Novel Techniques (2022, January 26), retrieved January 26, 2022 from https://phys.org/news/2022-01-binary-black-hole-behavior-revealed .html
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