National Geographic News
The Large Magellanic Cloud is indicated with a laser, and the Small Magellanic Cloud can be seen at right.
An artificial laser points out the Large Magellanic Cloud, with the Small Magellanic Cloud to its right.

Photograph courtesy ESO

Andrew Fazekas

for National Geographic News

Published July 21, 2011

A galactic crime involving hundreds of stolen stars has been uncovered 160,000 light-years away—and space sleuths believe they've caught their thief red-handed.

The suspect appears to be the Large Magellanic Cloud, one of the Milky Way's companion galaxies, while the victim is another nearby galaxy—the Small Magellanic Cloud. (See galaxy pictures.)

While surveying nearly 6,000 stellar giants in the neighboring large galaxy, astronomers came upon the crime scene using the 4-Meter Victor M. Blanco Telescope in Chile. The team discovered that more than 5 percent of the galaxy's stars were spinning in the wrong direction.

Meanwhile, analysis of these oddball stars' light signatures, or spectra, revealed a very different chemical makeup compared with most stars in the large cloud. For example, the oddities had much lower amounts of heavier elements such as iron and calcium.

What the scientists soon realized is that the stars' compositions were instead dead ringers for those of stars in the Small Magellanic Cloud—suggesting the odd stars had been gravitationally whisked away by the larger galaxy.

(See "'Vampire' Stars Found in Heart of Our Galaxy—A First.")

"According to current computer models, the two magellanic clouds appear to have passed close to one another about 1.2 billion years ago," said study co-author Robert Blum, an astronomer at the National Optical Astronomy Observatory in Tucson, Arizona.

"In a way analogous to the tides on the Earth caused by the moon and sun, these galaxies cause mutual tides as they interact, and they came close enough that the tidal force stripped stars off of the smaller [cloud], and these were captured by the [larger cloud]. "

Cloud Flyby Sent Shocks Through Space

Blum believes the stripping of stars occurred over a long period of time, perhaps a few hundred million years. Such a close interaction would have sent intense shockwaves through the satellite galaxies and led to bursts of star formation.

(Related picture: "Colliding Galaxies Ignite Stellar Nurseries.")

There is compelling evidence that this kind of stellar thievery may be common in the universe, Blum added. Astronomers should expect to find proof of it if they look carefully enough.

"Anytime we get to observe such fundamental phenomena in the sky and we find unexpected results, it is exciting," Blum said.

"To be able to piece together the story of a violent collision between galaxies from earthbound instruments one billion years after the fact is just amazing."



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