A telescope on Mauna Kea and a number of amateur astronomers have discovered a rare star that is racing toward the edge of the galaxy at an almost unprecedented speed.

Using instruments at the WM Keck Observatory on Mauna Kea and the Pan-STARRS Observatory on Haleakala, astronomers discovered a star racing through space at about 2.1 million kilometers per hour, or about 0.1 percent of the speed of light.

“That’s incredibly fast,” said Keck chief scientist John O’Meara. “I think it’s about Mach 1,700.”

Hyperspeed stars – stars that move twice as fast as the general background motion of all celestial bodies orbiting the center of their galaxy – are rare enough on their own, but O’Meara said this star is particularly interesting because of its small size.

The “subdwarf” star is only slightly larger than the planet Jupiter, which suggests that the star is very old.

“It’s fun because we don’t know how it could have moved so fast,” O’Meara said, but added that there are two common theories among astronomers.

The first theory, according to O’Meara, is that the star was once part of a pair of stars that orbited each other very quickly. One of the stars exploded in a supernova and hurled its partner into the cosmos.

“This is probably a bad analogy, but it’s like being on a carousel that’s going at high speed and then someone blows it up,” O’Meara said.

The second theory is that the star was part of a globular cluster of several stars, creating a complex gravitational interaction that could catapult a lower-mass star out of the cluster at high speed.

O’Meara said astronomers are working to “turn back the clock” and search the star’s trajectory for evidence of such a cluster.

Almost as unusual as its origin is its future: the star’s speed and trajectory indicate that it could leave the Milky Way completely.

“We do not expect many stars to leave the Milky Way, because if that happened often, we would not have a Milky Way,” O’Meara said. “It’s like we don’t expect to just throw Mars out of the solar system.”

While the star was observed by a team of astronomers led by a University of California professor using Keck and Pan-STARRS astronomy, the original discovery was made by a group of citizen scientists as part of a project called Backyard Worlds: Planet 9, in which amateur astronomers sift through thousands of images of space to identify stellar movements.

“It’s really cool to see a project like this find something that looks really weird and then upon closer inspection realize that it actually is really weird,” O’Meara said.

Email Michael Brestovansky at [email protected].