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Most of the stars in the Milky Way Galaxy move at speeds that depend on how far they are from the galaxy’s heart. But some stars strike out on their own. They can zip along many times faster than the others — and in all different directions.
Most of these stars move at up a few hundred thousand miles per hour relative to the stars around them. The fastest tops out at about four million miles per hour. Some of these stars are moving fast enough to leave the Milky Way behind — and streak into the space between galaxies.
Astronomers have identified at least three ways to give a star such a strong kick.
One is an encounter with the supermassive black hole at the center of the Milky Way. It’s four million times the mass of the Sun, with a powerful gravitational pull. As a binary star system approaches it, the black hole may grab one of the stars and give the other a boost away from it.
A second way is a bit of gravitational acrobatics among three or more stars. That can juggle the orbits of some of the stars, but shove one of them away from the others.
And the third way involves a stellar explosion. When a massive star explodes as a supernova, it loses most of its mass. That means its gravity isn’t as strong. So a companion star could zip off in a straight line — away from the explosion. And the shockwave from the explosion could add to the kick — perhaps punting the companion out of the galaxy.
Script by Damond Benningfield