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Hypervelocity stars are massive stars that move away quickly enough to leave the gravitational pull of our galaxy. Astronomers have found less than 30 of these strange stars. (Credit:
Astronomy: Roen Kelly)
The Milky Way contains billions of stars. Although the vast majority of them are linked to the galaxy by gravity, astronomers have found a few dozen stars that are not in orbit but are fleeing our galaxy at extreme speeds. These hypervelocity stars have intrigued researchers for years and a mysterious new player is entering the game. LAMOST-HVS, the star closest to our sun, has a very different history of origin from the how we believed that these stars were doing well in the Milky Way game.
In a study conducted by researchers at the University of Michigan and published March 12 in the Astrophysical Journal, astronomers used the data from the Magellan telescope in Chile and the Gaia satellite of the European Space Agency to go back in time and trace the trajectory of LAMOST-HVS, a 8.3 m solar mass star flying far from the galaxy at over 350 miles per second (568 kilometers per second). LAMOST-HVS is the closest hypervelocity star to the sun, and researchers believe that it was sent by an event that occurred 33 million years ago. But this event, it seems, was different from the one origin that astronomers developed to determine how hypervelocity stars are ejected from the galaxy, suggesting that there might be more of a problem. a way to chase a star from the Milky Way.
Scientists have traced the path of a huge "hyper-packed star". The star's past shows that it was ejected from the Milky Way disk, and not from the galactic center as previously thought. (Credit: Kohei Hattori)
Gravitational Fronde
Gravity is a force that brings things together. But this can also, under the right circumstances, push them at high speeds, sending them back instead via a slingshot effect. The traditional image of making hypervelocity stars begins with a system of binary stars. If this system passes too close to the supermassive black hole in the center of the Milky Way, which contains 4 million solar masses, the immense gravity can tear the binary. One star is caught by the black hole, while the other is projected at an incredible speed. It takes a huge black hole to get there. This is why astronomers felt that the central black hole of the Milky Way was the only possible explanation.
But after retracing the LAMOST-HVS movement in the past, the researchers discovered that his journey had begun in the Milky Way disk, not near the central bulge where the supermassive black hole is located. This excludes the supermassive black hole as the object responsible for its momentum … so what more?
Because a high gravity is needed to launch a star at such a high speed, a supernova star-shaped black hole or a few even relatively large stars will not do it. But, suggest the authors, a massive star cluster sheltering several very massive stars of at least 30 solar masses each could generate enough typing if LAMOST-HVS swayed too close to them. Another, even more exotic, solution would be to make a meeting with an intermediate mass black hole of about 100 solar masses.
Middle-mass black holes have been theorized for years, and although some evidence suggests their existence, they have not yet been unequivocally confirmed. However, it is thought that they form massive star clusters, such as the one that ejected LAMOST-HVS, so that the idea that one can be responsible for the current state of the star is not impossible.
Norma's spiral arm is partially obscured by dust and materials in the center of the galaxy. (Credit:
NASA / JPL-Caltech / R. Injured, Tobias Frei)
Point of origin
The essence of this discovery goes back to the origin of LAMOST-HVS, which the team found at a position in the Norma spiral arm of the Milky Way. But there is no huge star cluster known at this location. However, this does not bring about a decisive result – such a group could easily be hidden from sight by dust in the Milky Way, between the Earth and Norma's arm, making it difficult to observe. But if the group can be found, the team adds, it could provide additional evidence to prove the existence of intermediate-mass black holes. In addition, if a massive group is to blame, it would reveal new clues as to how these groups affect the environments of the galaxies in which they reside.
Regardless of how LAMOST-HVS was launched on its current path, one thing is certain: it has not been confronted with the supermassive black hole of our galaxy.
"This discovery radically changes our view of the origin of rapidly moving stars," said co-author Monica Valluri of the Department of Astronomy at the University of Michigan in a press release. "The fact that the trajectory of this huge fast-moving star is rooted in the disc rather than in the galactic center indicates that the extremely extreme environments needed to eject fast-moving stars may occur elsewhere than at the other end of the spectrum. around supermassive black holes. "
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