Hypervelocity stars can travel through space fast enough to overcome the escape velocity of their home galaxies, hence the term "unbound." (Some of the rogue stars in our galaxy may have originated in the Magellanic Cloud!) US 708, the fastest known unbound star in the Milky Way, is heading toward intergalactic space at a blistering 2.6 million miles per hour (4.2 million kilometers per hour). It's a hot subdwarf star that consists mostly of helium, but astronomers speculate that it may have started out as a red giant.
Hyper-Velocity Stars Are Escaping Their Home Galaxies
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Key Facts In This Video
The star US 708 is moving at 745 miles per second (1,200 km/sec) toward intergalactic space. 00:25
US 708 may have originally been a red giant in a binary system with a white dwarf. 02:50
Astronomers analyze Type 1A supernovae to calculate how far away other galaxies are, and how fast they're moving. 03:49