Survey spots dwarf stars moving fast enough to exit the galaxy

Vanderbilt University

A new analysis of a survey of the stars in our galaxy has found a number that appear to have reached escape velocity, moving fast enough to exit the Milky Way. These aren't the first stars we've found that are moving this quickly, but all the previous ones are large, blue stars that were thrown out of the galaxy's core by its supermassive black hole. These are smaller stars, similar to our Sun, and they clearly do not originate at the galaxy's core. In fact, they're moving fast enough that they could have potentially originated in another galaxy.

The study relies on the Sloan Extension for Galactic Understanding and Exploration, a project that has mapped the location of 240,000 stars within our galaxy. With multiple exposures, it's possible to track stars as they move across the sky.

The authors of the new study limited their analysis to G- and K-class stars, those similar in mass to the Sun and often referred to as G and K dwarfs. Even so, that limitation provides a lot of candidates; there were about 43,000 G dwarfs alone in the survey's population. From there, the authors converted the apparent motion of the stars to motion relative to the galactic core. They could then identify those stars that are moving very quickly relative to the galaxy itself. They took only those stars that were clearly moving fast enough to escape our galaxy's gravitational clutches—600 kilometers a second and up.