Can people leave the Milky Way

Rocket stars

Nashville (USA) - There are also outliers among the stars: While our sun moves its calm, round orbit around the center of the Milky Way - just like tens of billions of other star systems - there are a few celestial bodies that race through our galaxy at enormous speeds. So far, 18 such "hyper-speed runners" were known. Now an international team of astronomers has been able to identify twenty new racing stars in a large-scale survey of the starry sky. As the researchers reported at the large biannual meeting of the American Astronomical Society, the newly discovered high-speed runners belong to a completely different star class and come from different directions. Such an unusual origin was only known from a single other high-speed runner. The researchers can still only speculate about the origin of the racing stars, they write in the “Astrophysical Journal”.

“The new hyper-fast runners are very different from the ones previously discovered,” says Lauren Palladino, who was still studying at Vanderbild University in Nashville and was the first author of the study. The hyper-speed runners known to date all belong to a certain class of giant stars and come from the center of our galaxy. These celestial bodies glow blue and are heavy, hot and short-lived. Astronomers suspect that the supermassive black hole in the heart of the Milky Way has got them going. With its more than four million solar masses, it has the power to extremely accelerate nearby stars. If, for example, two stars in a binary system get close to the black hole, it can happen that one is sucked in by the black hole, while the other gains enormous momentum and is ejected from the center of the Milky Way.

The twenty new racing stars, however, are significantly smaller than the fast blue giant stars. They also do not come from the direction of the center of the Milky Way, but have very different orbits. These stars are the same size as our sun, but can travel up to several million kilometers per hour. This makes them fast enough to be able to leave the Milky Way. For comparison for these extreme speeds: A rifle bullet flies at around 1,000 kilometers per hour. The fastest manned rocket aircraft, the American experimental jet X-15, achieved over 7,000 kilometers per hour, the Saturn-5 lunar rocket 40,000, and the International Space Station is traveling at 27,000 kilometers per hour. The fastest man-made object at the moment is the Juno space probe (Jupiter Polar Orbiter). It is on its way to Jupiter at a good 100,000 kilometers per hour after it has gained momentum while flying past Earth - similar to the blue high-speed runners at the black hole. Our earth moves around the sun at a comparable speed, while our solar system rotates around the Milky Way eight times faster.

According to the researchers, various mechanisms can be considered as the cause of the high speeds of the stars. In a supernova explosion in a close binary star system, for example, the surviving star could be catapulted out. Or smaller black holes, many of which are in the galactic disk, could produce effects similar to the huge one in the center of the Milky Way. Some astronomers have also suspected that these stars might not come from the Milky Way, but from outside. The analyzes to date indicate, however, that the raging stars do not differ in their composition from ordinary stars on the galactic disk. However, the data are not yet final. The mapping of the starry sky - called the Sloan Digital Sky Survey - has been going on for several years. “In order to precisely determine the speed of a star, you have to measure its position over decades,” says Palladino. Therefore, some of the racing stars could turn out to be measurement errors. But even if further measurements are necessary: ​​Most of them should really be rocket stars. And no one seems to be heading for Earth.

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