Hypervelocity Stars in the Milky Way

Astronomers Keith Hawkins of Ohio University and Adam Kraus of the University of Hawaii think they have found half a dozen stars with masses similar to the Sun that are rocketing away from the core of Milky Way at speeds up to 3.2 million kilometers per hour. If their findings are confirmed, these will be the first known “hypervelocity stars” in this mass range. These fast movers are thought to form when the supermassive black hole at the center of the galaxy consumes one star in a binary system and ejects the other star.

“These are incredibly fast-moving objects that are actually gravitationally

unbound to the Milky Way,” Hawkins said during the 221st annual meeting of the American Astronomical Society in Long Beach, CA in early January.

Previously, astronomers looking for hypervelocity stars searched for bright, blue stars of 3-4 solar masses in places they weren’t supposed to form. Because of the abundance of sun-like stars in the galaxy, identifying hypervelocity stars in this mass range is more difficult. Using the 5.1 meter Hale Telescope at Mount Palomar, Hawkins and Kraus found 130 stars near the black hole at the center of the Milky Way that had traveled vast distances. They narrowed that grouping down to six stars traveling at speeds consistent with escape velocity from the galactic core.

Hawkins said that while new results are intriguing, they still need to be confirmed. If the findings are verified, they may provide insights into the types of stars forming in the center of the galaxy and also help astronomers estimate the size of the black hole at the Milky Way’s core.