Surrounding the supermassive black hole in the Milky Way, astronomers have discovered a new star shooting at more than 24,000 kilometers per second, or about 8% of the speed of the light ! But that's not all.
While the supermassive black hole at the center of our galaxy is a relatively quiet object compared to others, its near surroundings remain quite wild. Even so, some stars do not hesitate to come and tickle the beast. These, called S-stars, move in highly elliptical orbits around the object, moving away and then getting dangerously close.
Thanks to these stars, astronomers can probe the properties of the invisible object around which they orbit. The most famous of these is probably the S2 star , so far considered the closest to the black hole. Its path indeed sometimes brings it closer to less than 20 billion kilometers of the cosmic ogre.
Of course, this "flirting" is not without consequences. With each pass, S2 takes a violent gravitational "kick", accelerating its speed to approximately 3% that of light! But it seems that an even more impressive group of stars is traveling around this same black hole.
Last year, a team led by astrophysicist Florian Peissker from the University of Cologne (Germany) presented one of them, called S62. During its 9.9-year journey around the black hole, it comes within less than 2.4 billion kilometers . For comparison, that's closer than the average distance from Uranus to the Sun. The star is then accelerated to more than 20,000 kilometers per second, or 6.7% of the speed of light .
But the researchers were not at the end of their surprise. Recently, they discovered five more impressive stars:S4711, S4712, S4713, S4714 and S4715.
Among them, S4714 is the most outstanding . Every 12 years, its orbit brings it back about 1.9 billion kilometers from the black hole. During this approach, S4714 reaches a speed of about 24,000 kilometers per second, 8% of the speed of light! It then gradually slows down, eventually moving more than 250 billion kilometers away from the black hole.
These extreme stars, the researchers note, could now be considered true "squeezars", objects first theorized in 2003.
At the time, astrophysicists Tal Alexander and Mark Morris had indeed proposed a class of stars evolving in very eccentric orbits around massive black holes . Studying them – if these stars exist – could then shed light on two important physical processes. On the one hand on the growth of massive black holes, and on the other hand on the effects of their very strong tidal forces on the surrounding stars.
For Florian Peissker, S4711 and S4714 are very serious candidates to be considered as such. Their orbital characteristics, he says, are consistent with the predictions of Tal and Morris in 2003.
So not only does this discovery prove to us that there are even more "daredevil" stars around our Galaxy's supermassive black hole, but it also gives us the first candidates for a type of star originally proposed nearly 20 years ago.
