A team of astronomers has discovered a new class of singular stars moving at such a high speed, the Milky Way Galaxy cannot maintain its grip on them.

According to a press release, the astronomers published their study on the "hypervelocity stars" in the Jan. 1 edition of the Astrophysical Journal. They also discussed their discovery at the 223rd annual meeting of the American Astronomical Society.

"These new hypervelocity stars are very different from the ones that have been discovered previously," study lead author Lauren Palladino, a Vanderbilt University graduate student, said in the release. "The original hypervelocity stars are large blue stars and appear to have originated from the galactic center. Our new stars are relatively small - about the size of the sun - and the surprising part is that none of them appear to come from the galactic core."

To reach the velocity needed to escape the Milky Way's gravitational pull, the hypervelocity stars must get a burst of speed in excess of a million miles per hour, relative to the galaxy's motion.

Under the supervision of Vanderbilt assistant astronomy professor Kelly Holley-Bockelmann, Palladino calculated the orbits of sun-like stars using the Sloan Digital Sky Survey.

"It's very hard to kick a star out of the galaxy," Holley-Bockelmann said in the release. "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."

In the center of the Milky Way is a black hole with the mass equivalent of four million suns and its gravitational pull is plenty to spur these hypervelocity stars. Palladino and her colleagues believe when a host star is pulled by the central black hole, its companion is flung at an incredible velocity. The study has identified a class of at least 20 of these stars, the team has to accurately measure each star's positioning in order to calculate speed.

"One caveat concerns the known errors in measuring stellar motions," Palladino said. "To get the speed of a star, you have to measure the position really accurately over decades. If the position is measured badly a few times over that long time interval, it can seem to move a lot faster than it really does. We did several statistical tests to increase the accuracy of our estimates. So we think that, although some of our candidates may be flukes, the majority are real."