The Theory of Relativity, published in 1905 by Albert Einstein, postulated the existence of gravitational waves—oscillations of the space-time fabric—and more than a century later, we have irrefutable evidence of it.
Now, a new study has managed to find clear indications of relativistic precession in the orbits of two colliding black holes.
The science and other stuff to know
Since gravitational waves were first detected in 2015, this has become a fertile field for modern astrophysics, allowing experts to spot phenomena they were previously blind to.
The merger of black holes is undoubtedly one of the most colossal and violent events that can be conceived. The apocalyptic dance that the two bodies perform as they approach their inexorable destiny, and the fusion itself, involves so much energy that the fabric of space-time is shaken as if it were a sheet.
Thanks to detectors called interferometers, we can track these events from Earth and find out what event gave rise to these waves and what region of the universe they come from. The GW200129 signal was detected in 2020 and comes from the deadly gravitational dance of two massive black holes.
Now, a team of researchers from Cardiff University observed a strange twisting motion in the orbits of two colliding black holes, a phenomenon predicted by Einstein, a press release states.
Their study, which has been published in Nature, deduced that, before merging, these black holes rotated, presenting what is known as relativistic precession: the tendency of an orbit to be perturbed and change cyclically. A top, for example, is a clear example: it begins to rotate on its vertical axis —not rotational— and eventually, the axis twists and begins to rotate. This happens with the orbits of all systems where the gravity of one body affects the other, and tends to be a negligible effect.
But the case of GW200129 is exceptional due to the speed of precession of the system; it is 10 billion times stronger than the fastest precession measured up to its detection—75 years.
In addition to continuing to provide evidence in favor of Relativity—one of the most complete physical theories and with the greatest predictive power—, this detection speaks of the ability that the gravitational wave field has developed to detect phenomena that are increasingly weaker at energy levels.
The refinement of data analysis techniques and the collaborations between the LIGO, Virgo, and KAGRA interferometers are making it possible to obtain more precise measurements.
The network of interferometers extended between the United States (LIGO), Europe (Virgo), and KASGRA (Japan) is currently out of service as they are carrying out maintenance on the delicate design of the experiment. They will retake data in 2023 and track new events of this type and, hopefully, many other unknown ones.
“So far most black holes we’ve found with gravitational waves have been spinning fairly slowly,” said co-author Charlie Hoy, in a press release. “The larger 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 how binaries form suggest this one was extremely rare, maybe a one in a thousand event. Or it could be a sign that our models need to change.”
The researchers hope to continue detecting phenomena of this type. After all, the first detection of something always gives us the wrong impression that what we have found is unique. Still, it is enough to refine our measurements and instruments to realize that it is just one more specimen among hundreds of thousands of others.