The result of the analysis of data for 26 years of astronomical observations was the official confirmation of the predicted by the general theory of relativity of the peculiarity of the motion of a star in the strong gravitational field of a supermassive black hole in the center of the Milky Way. This is reported in an article in the scientific journal Astronomy & Astrophysics.
The object of research for scientists all these years has been the star S2, located next to the supermassive black hole Sagittarius A *, located in the galactic center of the Milky Way. The black hole has a mass four million times the mass of the Sun and is located 26 thousand light years from Earth. The S2 star itself, which belongs to spectral type B, is one of the most studied stars belonging to the S-cluster, a group of fast-moving stars discovered in 2002.
“This is only the second approach between S2 and a black hole that we have been able to trace. On the other hand, instrument accuracy has improved markedly over the past ten years, allowing this meeting to be tracked at ultra-high resolution. We have been carefully preparing for this event for several years, because it allows us to test in practice the peculiarity of relativistic effects,”said Reinhard Gentzel from the Max Planck Institute for Extraterrestrial Physics in Garching (Germany).
The black hole is surrounded by several dozen stars and several large clouds of gas, which periodically approach it at a dangerous distance. According to Einstein's general theory of relativity, these encounters and the relativistic effects associated with them will have a special effect on the star's orbit, displacing its pericenter. And scientists were able to confirm this in practice.
In 2003, the star approached the black hole at a dangerous distance, which for the first time allowed astrophysicists to track whether its trajectory changed under the influence of the black hole's gravity. The next rapprochement of the star with Sagittarius A * took place only in May of this year, for which scientists have been preparing for a very long time and carefully. The event was followed by several of the world's leading telescopes.
Hubble, VLT and other major Earth observatories have begun to conduct near-constant observations of S2 since April this year using SINFONI, GRAVITY and NACO instruments operating in the infrared and near infrared ranges of the spectrum.
Critical was the data collected in May 2018, when the star approached the black hole less than 20 billion kilometers away. The effect of interaction between the black hole and the star was so strong that the black hole accelerated the speed of the latter to 25 million kilometers per hour (almost 3 percent of the speed of light).
Promotional video:
Scientists note that the interaction, in particular, manifested itself in a sharp change in the color of the star under the influence of the so-called gravitational redshift - "stretching" of electromagnetic waves when they hit an area with a strong gravitational field. In the case of S2, the star noticeably “reddened” as it approached Sagittarius A *, after which, after a while, it acquired its usual color. The strength of this effect, as shown by VLT observations, was fully consistent with what the theory of relativity and the associated phenomenon of gravitational time dilation predicted.
“Our initial observations of S2 with the GRAVITY instrument began about two years ago. Even then, we identified a clear redshift effect associated with a black hole, which once again confirmed Einstein's general theory of relativity,”says astrophysicist Frank Eisenhower, who works with the GRAVITY and SINFONI spectrographs.
"During our closest approach, we even noticed a faint glow around the black hole in most of the images, which allowed us to very closely track the star's orbit and eventually witness S2's gravitational redshift."
Similarly, scientists have confirmed that S2's motion has deviated from its usual Newtonian orbit by the amount that was calculated using Einstein's calculations. Both, according to Genzel and his team, once again proves that Einstein is right in describing how the fabric of space-time and the entire Universe behaves.
The researchers say they now have a natural laboratory for the study of supermassive black holes and relativistic effects.
Nikolay Khizhnyak