Galaxy Sports Vast Comet-Like Tail
This composite image shows a tail that has been created as a galaxy plunges into the galaxy cluster Abell 3627. X-rays from Chandra (blue) and optical light (white and red) from the SOAR telescope show that as the galaxy plummets, it sheds material and forming stars behind it in a tail that stretches over 200,000 light years long. This demonstrates that stars can form well outside of their parent galaxy.
Credit: NASA/CXC/MSU/M. Sun et al.

Orphaned stars are being born in a vast tail of material stretching behind a faraway galaxy, astronomers said today.

The finding is evidence that orphaned stars?those not orbiting the center of a galaxy in normal fashion?are much more common than thought.

The feature extends for more than 200,000 light-years and was created as gas was stripped from the galaxy. For comparison, our solar system is about 26,000 light-years from the center of the Milky Way, and we're said to be in the galactic outskirts.

"This is one of the longest tails like this we have ever seen," said Ming Sun of Michigan State University, who led the study. "And, it turns out that this is a giant wake of creation, not of destruction."

Millions of stars

The comet-like tail was observed in X-ray light with NASA's Chandra X-ray Observatory and in optical light with the Southern Astrophysical Research (SOAR) telescope in Chile.

The observations indicate that the gas in the tail has formed millions of stars. Because the large amounts of gas and dust needed to form stars are typically found only within galaxies, astronomers had thought it unlikely that large numbers of stars would form outside a galaxy.

"This isn't the first time that stars have been seen to form between galaxies," said team member Megan Donahue, also of MSU. "But the number of stars forming here is unprecedented."

The parent galaxy, called ESO 137-001, is about 220 million light-years from Earth. It is plunging toward the center of Abell 3627, a giant cluster of galaxies.

The evidence for star formation in the galaxy's tail includes 29 regions of ionized hydrogen glowing in optical light, thought to be from newly formed stars. X-rays emanating from two of these regions also suggest starbirth.

Young stars

The researchers believe the orphan stars formed within the last 10 million years or so. Our sun, for comparison, is about 4.6 billion years old.

The stars in the tail of this fast-moving galaxy would be much more isolated than the vast majority of stars in galaxies.

"By our galactic standards, these are extremely lonely stars," said Mark Voit, another team member from MSU. "If life was to form out there on a planet a few billion years from now, they would have very dark skies."