A telescope on Maunakea and a host of backyard astronomers have detected a rare star racing toward the edge of the galaxy at nearly unprecedented speeds.
Astronomers using instruments at both the W. M. Keck Observatory on Maunakea and Pan-STARRS on Haleakala found a star blasting through space at about 1.3 million miles per hour, roughly 0.1% the speed of light.
“It’s wicked fast,” said Keck Chief Scientist John O’Meara. “I think that’s something like Mach 1,700.”
Hypervelocity stars — that is, stars moving twice as fast as the general background motion of all celestial objects orbiting the galactic center — are rare enough as it is, but O’Meara said this star is especially interesting because of its small size.
The “subdwarf” star is only barely larger than the planet Jupiter, which suggests the star is very old.
“It’s fun because we don’t know how it got moving this fast,” O’Meara said, although he added that astronomers have two prevailing theories.
The first theory, O’Meara said, is that the star was once part of a pair of stars orbiting each other very quickly. One of the stars exploded in a supernova, flinging its partner into the cosmos.
“This is probably a bad analogy, but it’s like if you’re on a merry-go-round going really fast, 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 speeds.
O’Meara said astronomers are working on “running the clock back” and looking back along the star’s trajectory for evidence of such a cluster.
Almost as unusual as where the star came from is where it’s going: The star’s speed and trajectory indicate that it could escape the Milky Way entirely.
“We don’t expect many stars to leave the Milky Way, because if that happened often, we wouldn’t have a Milky Way,” O’Meara said. “It’s like how we don’t expect to just yeet Mars out of the Solar System.”
While the star was observed by a team of astronomers using Keck and Pan-STARRS — who were led by a University of California professor — the initial discovery was made by a group of citizen scientists through a project called “Backyard Worlds: Planet 9,” in which amateur astronomers pore through thousands of images of space to identify movement among the stars.
“It’s really neat to see a project like this find something that looks really weird and then to take a closer look and find that it actually is really weird,” O’Meara said.
Email Michael Brestovansky at mbrestovansky@hawaiitribune-herald.com.