The fastest moving star in the Milky Way

Milky Way

Around the supermassive black hole of the Milky Way, astronomers have discovered a new star speeding at more than 24,000 kilometers per second, or about 8% of the speed of light! But that’s not all.

While the supermassive black hole in the center of our galaxy is a relatively calm object compared to others, its immediate surroundings are still quite wild. Even so, some stars do not hesitate to come and titillate the beast. These, called S stars, move in strongly elliptical orbits around the object, receding and then approaching dangerously.

Using these stars, astronomers can probe the properties of the invisible object around which they orbit. The most famous of these is arguably the star S2, until now considered the closest to the black hole. Its path indeed brings it closer sometimes to less than 20 billion kilometers of the cosmic ogre.

Obviously, this “flirtation” is not without consequence. With each pass, S2 takes a violent gravitational “kick”, accelerating its speed to about 3% that of light! But it looks like an even more impressive group of stars are traveling around this same black hole.

New record

Last year, a team led by astrophysicist Florian Peissker from the University of Cologne (Germany) introduced us to one of them, called S62. During its 9.9-year journey around the black hole, it comes within 2.4 billion kilometers of it. For comparison, this is closer than the average distance between Uranus and the Sun. The star is then accelerated to over 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 other even more impressive stars: S4711, S4712, S4713, S4714 and S4715.

Among them, S4714 is the most remarkable. Every 12 years, its orbit brings it about 1.9 billion kilometers from the black hole. During this approach, S4714 reaches a speed of approximately 24,000 kilometers per second, or 8% of the speed of light! It then gradually slows down, eventually moving more than 250 billion kilometers away from the black hole.

The first “squeezars”

These extreme stars, the researchers note, could now be considered real “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. Their study – 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.

Thus, not only does this discovery prove to us that there are even more “daredevil” stars around the supermassive black hole of our Galaxy, but it also gives us the first candidates for a type of star initially proposed almost 20 years old.

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