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Half of All Stars Are Drifting in Empty Space, Free of Galaxies

Stashed in: Stars!, Astrophysics, The Universe

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Stars are torn from their galaxies much more often than previously thought. 

As many as half of all stars in the universe lie in the vast gulfs of space between galaxies, an unexpected discovery made in a new study using NASA rockets. These stars could help solve mysteries regarding missing light and particles that theory had suggested should exist, scientists say.

In the study, astronomers investigated the extragalactic background light, the sum of all light emitted by stars in the universe throughout history. Prior research had detected fluctuations in this light that did not appear to come from any known galaxies. Scientists had suggested these fluctuations might come from primordial galaxies, the very earliest galaxies, whose light has yet to be detected.


The so-called "photon underproduction crisis" suggests that an extraordinary amount of ultraviolet light appears to be missing from the universe.

The intergalactic stars could also help address what is known as the "missing baryon problem." Baryons are a class of subatomic particles that includes the protons and neutrons that make up the hearts of atoms inside normal matter. Theories of the formation and evolution of the universe predict there should be far more baryons than scientists currently see. The baryons that astronomers have accounted for in the local cosmic neighborhood are only half of those predicted to exist in that region.

The study's scientists are now analyzing data from other instruments on the two sounding rockets they launched, as well as results from two other sounding rockets they sent into space. "We hope to learn more about how these stray stars are produced," Bock said.

The researchers detailed their findings in the Nov 7 2014 issue of the journal Science.

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