Astronomers this week revealed that they have discovered a new type of star traveling fast enough to leave the Milky Way galaxy. The stars, dubbed "hypervelocity stars," are different than other stars found traveling at such speeds as they did not come from the center of the galaxy.
"These new hypervelocity stars are very different from the ones that have been discovered previously," said Lauren Palladino, lead author of a paper on the stars published this month in the Astrophysical Journal and a graduate student at Vanderbilt University. "The original hypervelocity stars are large blue stars and appear to have originated from the galactic center."
The only current way that Astronomers know stars can reach escape velocity for our galaxy involves an interaction with the supermassive black hole at its center. Past research has found at least 18 hypervelocity stars that fit this standard profile and originate from the center of the galaxy.
"It's very hard to kick a star out of the galaxy," said Kelly Holley-Bockelmann, a co-author of the study and an astronomer at Vanderbilt. "The most commonly accepted mechanism for doing so involves interacting with the supermassive black hole at the galactic core. That means when you trace the star back to its birthplace, it comes from the center of our galaxy. None of these hypervelocity stars come from the center, which implies that there is an unexpected new class of hypervelocity star, one with a different ejection mechanism."
The new study's authors believe they have found 20 new stars that are moving at hypervelocity speeds within the Milky Way galaxy. These stars are closer in composition to main sequence stars such as the sun rather than the massive blue stars seen flung out of the galactic core.
Palladino and her colleagues are now performing follow-up observations on the new hypervelocity stars in order to determine their origin. One hypothesis currently floated by astronomers is that these objects may have originate outside of our galaxy.