X rays point to difficult stellar birth
A hot region in a cold cloud hints that a force other than gravity is helping to grow a star in a nearby stellar nursery.
March 2, 2005
Five hundred light-years from Earth, the R Coronae Australis star-forming region glows hazily in near-infrared light. Astronomers are surprised to detect X rays coming from a part of this cloud containing a protostar that has only just begun to form.
Photo by University of Hawaii / K. Nedachi, et al.
|March 2, 2005|
A collapsing protostar, still millions of years from becoming a full-fledged star, is emitting X rays, and astronomers are puzzled why. X rays generally come from hot, energetic objects — and this object dwells inside a cloud with a temperature of about -400° Fahrenheit (33 kelvins).
"We're seeing embryonic star formation," says Kenji Hamaguchi at NASA's Goddard Space Flight Center, the lead author on a report due for publication in The Astrophysical Journal. "Detecting X rays this early indicates gravity is not the only force shaping young stars." The researchers calculate material is merging into the stellar embryo, designated IRS7B, about 10 times more energetically than gravity alone would account for and they suspect tangled magnetic fields may be responsible.
The international team of astronomers used the XMM-Newton satellite observatory to detect X rays coming from the R Coronae Australis star-forming region, and the orbiting Chandra X-ray Observatory to pinpoint the location. Follow-up infrared observations with the ground-based Subaru Telescope on Mauna Kea showed IRS7B belongs to Class 0, the youngest kind of protostar, and less than 100,000 years have passed since it began to form.
"This is no gentle infall of gas," says Michael Corcoran, a team member also based at Goddard. "The X-ray emission shows that forces appear to be accelerating matter to high speeds, heating regions of the gas cloud to 100 million degrees Fahrenheit."
Blue blobs indicate X rays from other protostars in the R Coronae Australis cloud. Five of these are further along in formation than IRS7B, and their X-ray emission poses fewer puzzles than IRS7B's X rays. TIn the larger version of this image, the inset, taken in infrared light, shows the warm cocoon around IRS7B (arrow).
Photo by ESA / XMM/Subaru / University of Hawaii
Solar flares that produce X rays may be a local example of this process, say the researchers. "Young stars have the same kind of activity as the Sun, but on a much larger scale," Corcoran told Astronomy.
Flares occur when loops of magnetism near the Sun's surface become knotted and snap, ejecting charged particles (electrons and ionized atoms) at speeds of millions of miles per hour. X rays fly when the fast-moving particles slam into the Sun's surface.
The researchers are uncertain where the charged particles, and the magnetic fields, come from. For the latter, there are two basic models, says Corcoran. One involves knots in the galactic magnetic field; the other, "the more likely," generates the fields by a dynamo in the protostar's core. The team hopes further studies of this cloud and others at X-ray energies will help clarify the picture.
Says Corcoran, "We have seen X rays from 3 or 4 other Class 0 objects, but never so clearly as this."