The invisible, dark-matter "halos" that surround galaxies may in fact contain a few stars, scientists at the University of California say.

The existence of stars in dark matter would explain why astronomers see more light than can be accounted for by existing galaxies, according to a report to be published in the journal Nature. The research was produced by scientists from UCLA, UC Irvine and elsewhere.

The new hypothesis rejects earlier theories such as light fluctuations from even more distant galaxies.

"Galaxies exist in dark-matter halos that are much bigger than the galaxies; when galaxies form and merge together, the dark matter halo gets larger and the stars and gas sink to the middle of the halo," said UCLA’s Edward L. Wright.

"What we’re saying is one star in a thousand does not do that and instead gets distributed like dark matter. You can’t see the dark matter very well, but we are proposing that it actually has a few stars in it — only one-10th of one per cent of the number of stars in the bright part of the galaxy."

These newly hypothesized stars could have come from cosmic collisions. As crashing galaxies became gravitationally tangled with one another, "orphaned" stars were tossed into space, the researchers say, producing the diffuse, blotchy light emitted from the galaxy halos.