The Milky Way’s Speediest Stars Could Solve a 50-Year-Old Mystery

May 9, 2018

By Shannon Hall

Ken Shen was racing against the sun. It was 3 A.M. on April 25 and Shen—an astronomer at the University of California, Berkeley—was sitting at his kitchen table in his pajamas. At that precise moment the scientists behind the European Space Agency’s Gaia spacecraft released the mission’s second batch of data. And Shen was on a mission to comb that data to find the Milky Way’s fastest-moving stars, then to verify their identities via independent observations on ground-based telescopes. With 30 minutes to go before the sun’s glare started to hit the west coast, Shen managed to find his first target and send its coordinates along to a collaborator at the Lick Observatory near San Jose.

But he could not crawl back into bed. For the next 24 hours Shen and his colleagues scoured the Gaia data for a handful of candidates to observe with telescopes in South Africa, the Canary Islands, Arizona and California. After a week of careful analysis the researchers were certain they had found three of our galaxy’s fastest stars. Not that they were only interested in speed: such rapid-moving stars were the smoking-gun evidence Shen was seeking for his novel theory of how certain stars explode. On April 30 the team posted their results to the preprint server arXiv and submitted them to The Astrophysical Journal for peer-reviewed publication.

Shen’s theory concerns type Ia supernovae, stellar explosions so consistently and uniformly bright that astronomers have used them as benchmarks to measure the vastness of the cosmos. Whether right here in the Milky Way or in a galaxy on the other side of the observable universe, these cataclysmic explosions always display almost the exact same luminosity, allowing precise calculations of their distances. Such work has demonstrated the universe’s expansion is accelerating—an advance that netted the 2011 Nobel Prize in Physics—and has helped validate the existence of dark energy. Type Ia explosions also create and disperse heavy elements (including the iron in the hemoglobin running through our veins), and so play crucial roles in studies of galactic evolution.

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