Space Is Filled With Orphaned Stars

When galaxies collide, some stars are flung from their homes and left to wander space alone.

A time-lapse photograph of the CIBER rocket launch, taken from NASA's Wallops Flight Facility in Virginia in 2013 (NASA/JPL-Caltech)

For billions of years, galactic train wrecks have scattered stars across the cosmos. Alone in space, the celestial orphans only dimly light their drift through the blackness. Now, after detecting the faint flickers, astrophysicists believe they have found that cosmic collisions may have left as many as half of all stars floating without a galaxy.

“The merging of galaxies is a messy process,” said Michael Zemcov, an astrophysicist from Caltech and lead author on the study published Thursday in Science. “Some of the stars mash together and form bigger galaxies, but some of them get tossed out completely and flung over very large distances.”

Many of the reclusive stars form dim halos around the galaxies in which they used to reside. Although astronomers previously knew about these halos, they were unsure of how many there were, because the light that singular stars emit gets drowned out by their much brighter neighboring galaxies.

As a part of their research into ancient galaxies, Zemcov and his team of scientists from the U.S., Japan, and Korea, launched a rocket equipped with a built-in telescope to take an enormous picture of space. The experiment, called Cosmic Infrared Background Experiment, or CIBER, had a field of view that was 20 times larger than the surface of the moon, according to Zemcov. It offered the team a single image of millions of galaxies.

When the team analyzed the data, they observed twice as much infrared light as they expected to find. To investigate the discrepancy, the team blacked out the light coming from the star clusters and observed that a lot of light seeped from between the galaxies.

An artist's concept of a number of galaxies sitting in huge halos of orphaned stars (NASA/JPL-Caltech)

“It’s like looking at a LiteBrite with all of the little pegs being galaxies with clusters of stars,” said Zemcov. “We masked the light emitted from the galaxies, or pegs, and expected to see a black screen, but actually there were small amounts of light still emitted.”

The findings stumped the team at first. Not until they eliminated several other possibilities did they deduce that the light was coming from large amounts of rogue stars. The research, they said, shows that there are much more solo stars out there than previously thought. Since orphaned stars can harbor orbiting planets, the researchers said that this finding may provide further insight into how many celestial objects wander the void of space.