collision inedite trous noirs précession théorie relativite einstein couv

One of the most extreme black hole collisions in the universe validates Einstein’s theory

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Einstein’s theory of general relativity had predicted the behavior of two black holes revolving around each other and adopting the phenomenon of precession (like an oscillating top), due to the emitted gravitational waves. Researchers recently provided the first physical evidence of this by observing a peculiar twisting motion in the orbits of two colliding black holes, an extremely rare phenomenon.

Precession is the phenomenon according to which a body in orbit – periapsis – around another (here they are two black holes) sees the ellipse describing its trajectory rotating slowly in the orbital plane of the object. This means that during the successive revolutions of the object, the direction described by the line – the apse – passing through the central body and the orbiting body at the moment they are closest, is not fixed, but varies. slowly.

Illustration of the phenomenon of precession of the periapsis: the periapsis (in blue) and the line of the apses rotate in the plane of the orbit over time. ©Wikipedia

A concrete example is the oscillation of a spinning top, or precession, once every few seconds. By contrast, precession in general relativity is usually an effect so weak as to be imperceptible, as Albert Einstein predicted in 1916. In fact, in the fastest known example, that of orbiting neutron stars, called binary pulsars, is It took more than 75 years. for the orbit to precess.

Recently, Cardiff University researchers report for the first time the observation of this effect in black holes, the binary system GW200129, where the spin is ten billion times faster than in previous observations. Their study is published in the journal Nature.

A gigantic collision of two black holes

The binary system GW200129 was discovered, on the occasion of its collision, by three gravitational wave detectors located in Italy, the United States and Japan (Advanced LIGO and Virgo) at the beginning of the year 2020. It is on these data that the team relied on dismantling the phenomenon of precession, which initially appeared as an undesirable noise in the analyses.

You should know that according to the theory of general relativity, a pair of black holes in orbit around each other lose energy by producing gravitational waves and end up merging. A key prediction in Albert Einstein’s theory of general relativity, gravitational waves are slight disturbances in the fabric of space-time caused by the very high-speed motion of high-mass objects. They propagate at the speed of light and travel for billions of years without being disturbed by anything. During these collisions, the black hole produced can be propelled by these waves like a rocket emitting gases.

Because of this, one of the black holes in GW200129 is probably the fastest rotating black hole ever observed, thanks to gravitational waves. And contrary to previous observations, this rapidly spinning black hole warped space-time so much that the entire orbit of the binary system swung back and forth. Professor Mark Hannam from Cardiff University’s Gravity Exploration Institute said in a statement: ” We always thought that binary black holes could do this. We expected to find an example of this from the first detections of gravitational waves. We had to wait five years and more than 80 separate detections, but finally we have one. “.

As mentioned above, gravitational waves were predicted by Einstein in 1916. They were first detected directly from the merger of two black holes by advanced LIGO (Laser Interferometer Gravitational-Wave Observatory) instruments in 2015, a groundbreaking discovery. which led to the 2017 Nobel Prize. Prize.

Dr Jonathan Thompson, also from Cardiff University, explains: This is a very difficult effect to identify. Gravitational waves are extremely weak and their detection requires the most sensitive measuring device ever. Precession is an even weaker effect buried in the already weak signal. So we had to do some careful analysis to find out. “.

A rare event that requires a model update

Since the discovery in 2020, several other scientists have been studying the initial gravitational wave data. Also, in May 2022, a study put this collision of the two black holes into an equation. He reported that the merger was massive and lopsided, as gravitational waves arose from the collision in one direction, as the new black hole resulting from this merger was likely “kicked out” of its home galaxy more than 4.8 million years away. km/h in the opposite direction.

The extreme collision and merger of the two black holes is an unprecedented event and significant enough to prove Einstein’s theory correct. However, as co-author Dr. Charlie Hoy explains: So far, most of the black holes we’ve found with gravitational waves have been spinning very slowly. The largest black hole in this binary, which was about 40 times more massive than the Sun, was spinning almost as fast as physically possible. Our current models of container formation suggest that this was extremely rare, perhaps one in a thousand. Or it could be a sign that our patterns need to change “.

Certainly, this discovery proves the truth of Einstein’s theory, but it also raises the question whether this type of unstable black hole merger is an exception or not. This is why the international network of gravitational wave detectors is being upgraded and will begin its next search campaign in 2023. These upcoming studies will determine if GW200129 is really a rare phenomenon or if it is more common than scientists think.

Source: Nature


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