Who says black holes are invincible? Black holes can also be "kicked" out of the galaxy at a speed of 5,000 kilometers per second!

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Like the recoil of a gun, the momentum loss of two black holes in a binary system gives the merged black hole a kick similar to recoil. Vijay Varma, an astrophysicist at Caltech and an incoming Klarman Fellow in Cornell University's College of Arts and Sciences, said: For some binaries, the "kick" can reach 5,000 kilometers per second, which is greater than the escape velocity of most galaxies. The study developed a new method that uses gravitational wave measurements to predict when the final black hole will remain in its host galaxy and when it will be ejected.

Such measurements could provide a critical missing puzzle piece behind the origins of massive black holes and offer insights into galaxy evolution and tests of general relativity. Varma is the lead author of a study published in the journal Physical Review Letters, Extracting Gravitational Recoil from Black Hole Merger Signals, with co-authors Maximiliano Isi and Silvia Biscoveanu of MIT. When black holes orbit in a binary system, their gravitational waves carry away energy and angular momentum, which causes the binary system to contract as it spirals inward.

When a system has asymmetries, such as unequal masses, gravitational waves are not emitted equally in all directions, which results in a net loss of linear momentum and thus recoil. Most recoil occurs near the merger, which can create a shock large enough to "kick" the newly merged black hole out of its host galaxy. The researchers' model is based on supercomputer simulations that numerically solve Einstein's equations of general relativity. These simulations are part of a larger study conducted under the Simulating Extreme Spacetimes (SXS) collaboration.

The collaboration includes research groups from Caltech and Cornell University, led by Saul Tekolsky, the Hans A. Bitt Professor of Physics at Cornell University. Tekolsky said: "This study shows that gravitational wave signals can be used to understand astrophysical phenomena in an unexpected way. People thought we would need to wait more than a decade to find detectors sensitive enough to do this kind of work, but this study shows that it can actually be done now, which is very exciting!"

Figure 3, Figure 4, Figure 5 Illustration: This simulation shows the merger of a 35 solar mass black hole and a 25 solar mass black hole, followed by the recoil (kick) the black holes experience after the merger. After the merger, the simulation was sped up to highlight this. The arrows represent the rotation (spin) of the black holes, which interact with the orbital angular momentum (pink arrows) to cause the orbital plane to wobble as the binary evolves. The blue and red spheres represent the gravitational wave patterns produced during the collision.

Although the existing publicly available gravitational wave signals from the LIGO and Virgo gravitational wave observatories are not strong enough to measure the recoil well, as these detectors improve in the coming years, this method will be able to reliably measure this "kick", and this "kick" has also embarrassed the invincible black holes, who have always been invincible. Black hole: I can actually be "kicked" out of the galaxy?

Boco Park | Research/From: Cornell University

Reference journal: Physical Review Letters

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