Multitudes of stars may be orphans

Even stars can get lost in space.

Scientists who shot a rocket up beyond Earth’s atmosphere for a matter of minutes have made a remarkable discovery about the diffuse background light that permeates the universe: As many as half of all stars may have been stripped from their home galaxies and flung into the darkness of the cosmos.

Astronomers were aware that some stars were intergalactic orphans. But the extent of the dim diaspora, reported in today’s edition of the journal Science, came as something of a shock.

“I did not expect it to be half the stars – I thought that most stars would be in galaxies,” said Harvey Moseley, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Md., who was not involved in the research. “It’s almost like they’re hiding.”

The new information could compel scientists to re-evaluate their theories of how the universe formed the galaxies we see today.

“If you want to understand what’s happening in the formation of galaxies, you can’t just look at the galaxies,” said study co-author James Bock, an experimental cosmologist at NASA’s Jet Propulsion Laboratory in La Canada Flintridge, Calif.

When astronomers study the light coming from Andromeda, our nearest galactic neighbor, stripped stars seem to contribute less than 5 percent of the galaxy’s total light, said Karoline Gilbert, an astronomer at the Space Telescope Science Institute in Baltimore who wasn’t involved in the research. As a result, scientists haven’t paid much attention to them.

Now it’s clear they can’t ignore them anymore. “There is still a large number of stars we aren’t accounting for,” she said. “We can’t ignore orphan stars.”