An international team of astronomers has viewed two distinct "tails" found on a long tail of gas that is believed to be forming stars where few stars have been formed before. The new observation was made by the Chandra X-ray Observatory and is detailed in a paper published this month in the Astrophysical Journal.

This gas tail was originally spotted by astronomers three years ago using a multitude of telescopes, including NASA's Chandra X-ray Observatory and the Southern Astrophysical Research telescope, a Chilean-based observatory in which MSU is one of the partners. The new observations show a second tail, and a fellow galaxy, ESO 137-002, that also has a tail of hot X-ray-emitting gas.

"The double tail is very cool – that is, interesting – and ridiculously hard to explain," said Donahue, a professor in Michigan State University's Department of Physics and Astronomy. "It could be two different sources of gas or something to do with magnetic fields. We just don't know."

What is also unusual is the gas tail, which is more than 200,000 light years in length, extends well outside any galaxy. It is within objects such as this that new stars are formed, but usually within the confines of a galaxy.

"This system is really crazy because where we're seeing the star formation is well away from any galaxy," Donahue said. "Star formation happens primarily in the disks of galaxies. What we're seeing here is very unexpected."

How these newly formed stars came to be in this particular place remains a mystery as well. Astronomers theorize this gas tail might have "pulled" star-making material from nearby gases, creating what some have called "orphan stars."

"This system continues to surprise us as we get better observations of it," Donahue said.
The gas tail is located in the southern hemisphere near a constellation called Triangulum Australe, in a giant cluster of galaxies called Abell 3627. It is associated with a galaxy known as ESO 137-001 which is about 219 million light years from our own Milky Way Galaxy.

Star formation is a continuous process throughout the universe, where there are estimated to be billions of galaxies, each of which contains billions of stars. Stars are formed from clouds of dusty, cool, dense molecular gas. Molecular gas clouds prefer to inhabit galaxies, particularly the disks of galaxies like the Milky Way.

Our sun, a star located within the Milky Way Galaxy, is an average-size star estimated to be about 4.6 billion years old.

Citation: M. Sun et al., 'SPECTACULAR X-RAY TAILS, INTRACLUSTER STAR FORMATION, AND ULXs IN A3627', The Astrophysical Journal, January 2010, 708, 946-964; doi: 10.1088/0004-637X/708/2/946