Gravitational waves: Black hole accelerated to 180,000 km/h after collision
Ten years after the first detection of gravitational waves, the speed at which two black holes catapult each other was determined for the first time.
(Image: Instituto Galego de FĂsica de Altas EnerxĂas (IGFAE))
An international research team has for the first time determined the speed and direction of the recoil with which a black hole was ejected from its surroundings after the collision of two progenitors. This has been made public by the University of Santiago de Compostela, where the work was led. This was achieved on the basis of gravitational waves, which we have only been able to measure for 10 years. The GW190412 signal observed in 2019 with the Advanced LIGO and Virgo detectors originated from the merger of two black holes, the end product of which was catapulted to 180,000 km/h. This was enough to hurl it out of its globular cluster.
Helpful for more classical astronomy
Gravitational waves are slight deformations of the fabric of space-time and were predicted by Albert Einstein's theory of general relativity. However, the physicist had assumed that they would never be detectable. However, thanks to highly sensitive measuring instruments, this is now possible – On September 14, 2015, gravitational waves were detected for the first time using the Ligo gravitational wave observatory (Laser Interferometer Gravitational Wave Observatory) in the USA. Just two years later, the Nobel Prize in Physics was awarded for this experimental proof. The Spanish university now explains that the recoil of two colliding black holes is one of the most dramatic elements of the underlying events, but has not yet been observed.
The method now being used was developed by the group led by physicist Juan Calderon-Bustillo back in 2018. It is based on the fact that gravitational waves look different from different directions. The group was certain that it would therefore be possible to determine the recoil, especially when two particularly dissimilar objects collide. This is exactly what was observed in mid-April 2019: the gravitational waves came from the collision of two black holes with very different masses. One had around eight times the mass of our sun, while the other had 30 times the mass of the sun. A three-dimensional representation of the event was meticulously mapped out. This is presented in the specialist journal Nature Astronomy.
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If the recoil and its direction can be determined more quickly in future, this could also help to find other signals of such events, the research team explains. This is because when a black hole formed in this way races at high speed through a comparatively dense environment such as a galaxy nucleus, signal flashes can occur. However, whether these can be detected from Earth depends on the direction in which the black hole is racing. If you know this, you can distinguish real signals of such an event from random signals coming from the same area in the night sky. Gravitational wave astronomy is therefore potentially even more powerful.
(mho)
