Stars on the run in hyperspeed

Discovered a surprising new class of hypervelocity stars, stars that move in a solitary fast enough to escape the gravitational embrace of the Milky Way.

Stars on the run in hyperspeed


Source: Julie Turner, Vanderbilt University / NASA / ESO

Plan view and cutting of the Milky Way with the positions and directions of some of the new class of hypervelocity stars. It is sun-like stars which travel at a speed of over a million and a half miles per hour relative to the galaxy enough to escape from the gravitational pull.

In 2005, it was discovered the first star hyper-fast, a massive star whose orbital speed of more than 3 million miles per hour – far more than enough to escape the gravitational pull of the galaxy – can be explained mainly by the acceleration from close encounter of a binary star with the supermassive black hole at the center of the Milky Way. Other specimens of these meteors were discovered during the following years, earning the nickname of stars exiles because, in fact, run out of the galaxy and destined to be lost in the void of intergalactic space.

The discovery of a new group of hypervelocity stars has now been published in the Astrophysical Journal, and described a few days ago at the annual meeting of the American Astronomical Society in Washington.

“These new hypervelocity stars are very different from those discovered earlier, “says Lauren Palladino, the young PhD student at Vanderbilt University in Nashville, USA, who led the research. “Those are great discoveries, originally blue stars appear to originate from the galactic center, while our new stars are relatively small – about the mass of the Sun – and the amazing thing is that none of them seems to come from the galactic core. ”

“It’s very difficult to throw out a star from its galaxy , ” adds Kelly Holley – Bockelmann of Vanderbilt University, who supervised the work of mapping the Milky Way Palladino carried out by the Sloan Digital sky Survey , a large census of stars and galaxies that covers about a quarter of the sky. ” The most accredited mechanism – explains researcher – involves interaction with the supermassive black hole in the galactic core. This means that if you trace the orbit of the star back to the point where she was born, she is seen coming from the center of our galaxy. Instead, none of the hypervelocity stars that we found comes from the core, which implies a new, unexpected, class of hypervelocity stars, with a different mechanism of expulsion. ”

So far we have identified 18 hypervelocity blue giant stars , a class of objects whose existence was predicted in 1988 , even before their observation , just on the basis of considerations on the dynamics of the interaction between a pair of stars and supermassive black holes . A swirling ballet in which one of the two stars is trapped in the gravitational field of the black hole ( becoming a significant part of the menu ), while the companion is thrown out of the galaxy at speeds approaching 1,000 kilometers per second.

Now Palladino and colleagues found 20 additional stars of solar size, each with a total speed exceeding 600 kilometers per second, are characterized hypervelocity as possible, and that further observations will be carried out to obtain more precise measurements. The new “exiled ”  star seem to have the same composition as a normal star grew up in a protostellar disk, like the one that took shape on the Sun, so scientists believe very unlikely to have originated in the nucleus of the galaxy, and even in some exotic place outside of the galaxy.

“The big question is: what drove these stars up to such extreme speeds? Now we are working to solve this dilemma, “says Holley – Bockelmann.

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