As part of the S5 project, aimed at observing luminaries in stellar streams, astronomers have discovered the fastest star called S5-HVS1 of the main sequence of all known, which rushes through our galaxy with a staggering speed of 1.7 thousand kilometers per second and eventually will leave Milky Way.
Besides the fact that this star is the fastest among her kind, it is also the first one about whom we can confidently say that it started her escape from the center of our Galaxy. This means that the star was probably involved in the interaction with the supermassive black hole Sagittarius A* in the heart of the Milky Way, which gave it this crazy speed.
Thanks to the satellite of the European space agency Gaia today, astronomers have already discovered several dozen stars racing through space at speeds from 1 to 2.4 thousand kilometers per second. The fastest among them are neutron stars and white dwarfs, the process of imparting acceleration to which is quite understandable and is associated with supernova explosions.
As for the stars of the main sequence, it is not so simple, since it is not yet clear how they can accelerate to such speeds without the energy of an explosion.
The previous record was US 708, whose speed is 1.2 thousand kilometers per second. Now S5-HVS1 has climbed the podium. It is 2.35 times more massive than the Sun and young is happy, its age is estimated at only 500 million years. She started her escape from the Galaxy about 4.8 million years ago with an initial speed of 1.8 thousand kilometers per second.
Astronomers believe that the main sequence stars with huge speeds, known at the moment, could be thrown out of their native neighborhoods during the exchange interaction of three bodies, where one of them is a black hole and the other two are a fugitive star and its companion.
The exchange interaction of three bodies between two stars and a massive black hole inevitably throws one of the stars from the galaxy. Since stars are finite in size, only an extremely massive and compact object can explain fugitives at speeds of a thousand kilometers per second.
– Warren Brown from the Harvard-Smithsonian Center for Astrophysics (USA) claimed in 2015
In their work, scientists calculated that in order to give the current speed to the S5-HVS1 star, kinetic energy transfer of about 6 × 1042 Joules would be required. For comparison, such a “kick” will accelerate the Earth to 0.997 the speed of light! But what triggered such a course of events?
The first idea is that initially the star S5-HVS1 was the main member of the binary system with a small companion that is smaller than the Sun and revolved around it with a period of 3 to 40 Earth days.
When a system of two stars approaches a supermassive black hole, one of its components is captured by a gravitational monster, and the second is thrown away at high speed. If the black hole has a mass of several million solar, the ejected star can reach a speed of a thousand kilometers per second or more.
Another possibility is that several million years ago, a relatively small black hole merged with the supermassive Sagittarius A *. This could lead to the ejection of a large number of stars from the center of the Milky Way. And, although today there is no convincing evidence of such an event, they can be obtained if similar S5-HVS1 bodies are detected.
Further observations of the S5-HVS1 star and, in particular, the next release of Gaia data will allow us to more accurately measure its three-dimensional position and speed and, therefore, it is better to simulate its orbit. In addition, the discovery of more analogues of S5-HVS1 will give clues about what is happening in the center of the galaxy.
S5-HVS1 – the fastest star escaping from the Milky Way
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