Astronomers have uncovered the dramatic story of a star hurtling at over 3 million km/h toward the edge of our Galaxy, 2,000 light-years from Earth. What propelled it into this high-speed escape?
Located about 2,000 light-years from Earth, LP 40−365 is a rare hypervelocity star. "This star is moving at almost three million kilometers per hour," explains JJ Hermes, associate professor at Boston University's College of Arts & Sciences. Its trajectory will eventually eject it from the Milky Way entirely. Researchers liken it to shrapnel from a supernova explosion. Findings are detailed in The Astrophysical Journal Letters.
Supernovae mark the explosive deaths of stars, triggered by two primary mechanisms: the core-collapse implosion of a massive star or the thermonuclear detonation of a white dwarf that accretes material from a companion. The latter involves a binary system, and LP 40−365 was once part of one such pair.
Using data from the Hubble Space Telescope and TESS exoplanet survey, Hermes' team found that LP 40−365 rotates once every nine hours while speeding outward. This spin, imparted by the supernova, offers clues to its origins.
In this scenario, a white dwarf in a tight binary orbit siphoned mass from its companion until it detonated. The blast tore a fragment from the donor star—LP 40−365—flinging it from the system and Galaxy.
While LP 40−365 is swift, others outpace it; recently, a star was observed at over 6 million km/h, likely disrupted by our Galaxy's supermassive black hole.
