Little Galaxy's Own Stars Cast 95 Per Cent of Its Oxygen Away

By Ken Croswell

Published on New Scientist (December 15, 2015)

Benefactors can be too generous. Exploding stars in a small galaxy called Leo P pumped out heavy elements with such vigour that most of them sailed off into space.

“It’s tough being a little galaxy,” says Kristen McQuinn at the University of Texas at Austin. Not only does a dwarf galaxy’s feeble gravity fail to retain debris from supernovae that explode within it, but giant galaxies such as the Milky Way can also raid the dwarf of stars and gas.

Dozens of dwarf galaxies orbit the Milky Way, and all have low levels of heavy elements. But we didn’t know how much of the dwarfs’ poverty to attribute to our Galaxy’s thieving ways, or how much material simply escaped.

Enter Leo P, a small galaxy 5.3 million light-years from Earth that astronomers spotted in 2012. “It’s the perfect laboratory,” McQuinn says: it lies just beyond the Local Group, the gathering of nearby galaxies that includes our own, so no other galaxy interferes with its development.

McQuinn and her colleagues decided to look at oxygen, the most abundant element heavier than hydrogen and helium. Using models of how much oxygen Leo P’s massive stars should have produced and subsequently cast out when they exploded, the team found that the galaxy has lost 95 per cent of its oxygen, even without the Milky Way’s meddling.

Still, similar galaxies orbiting the Milky Way have lost 98 to 99 per cent of their heavy elements. “Leo P has been wise to keep its distance from us,” McQuinn says.

Ken Croswell earned his Ph.D. in astronomy from Harvard University and is the author of The Alchemy of the Heavens and The Lives of Stars.

"An engaging account of the continuing discovery of our Galaxy...wonderful." --Owen Gingerich, The New York Times Book Review. See all reviews of The Alchemy of the Heavens here.

"A stellar picture of what we know or guess about those distant lights."--Kirkus. See all reviews of The Lives of Stars here.

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