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	Powerful Flare From A Brown Dwarf Star Shocks Scientists Using the Chandra X-ray Observatory By Maia Weinstock Staff Writer posted: 07:00 pm ET 12 July 2000

Brown Dwarf Flare

The night of December 15, 1999 was supposed to be just another night at the lab for Bob Rutledge and several colleagues who were working with images from the Chandra X-ray Observatory. But when a tiny white dot suddenly appeared in their data, the session became anything but routine.

The dot was a cosmic flare, like the ones often seen emanating from our own sun. But this was no ordinary flare, for it was coming from an unlikely source a brown dwarf, or failed star, some 16 light-years from Earth. Indeed, the astronomers soon realized that they had just made the first-ever observation of a brown-dwarf X-ray flare, a discovery that may change their understanding of brown dwarfs and other stellar objects forever.

Brown dwarf LP 944-20 dramatically made its presence known last December when it suddenly erupted with X-ray light.

"We were shocked," said Rutledge, who is an astronomer at the California Institute of Technology (Caltech) in Pasadena. "Shocked, because we had not expected flaring from such a lightweight object, and glad because it was clear we had happened upon something completely new. It was the kind of moment observers love."

The flare appeared nine hours into the astronomers 12-hour observation of brown dwarf number LP 944-20, which is located in the constellation Fornax in the southern skies. After nine hours of seeing nothing special, a bright flare of X-rays taunted the scientists, appearing briefly as an intense flash before fading out over the following two hours. Thankfully, Chandra recorded the entire episode, so the astronomers were able to go back later and interpret the flash.

"It seemed fantastically bright and hard to believe," said University of California at Berkeley astronomer Gibor Basri, who contributed to the finding. "The first feeling is always one of skepticism: can this be real? But then it began to sink in that it was real and pretty surprising."

LP 944-20 has about 60 times the mass of planet Jupiter, or 6 percent of our suns mass. As such, the object is tantalizingly close to the star/brown-dwarf boundary (it is only 10 Jupiter-masses short of star-status). For this reason, it is extremely interesting for astronomers to study.

Brown dwarfs (center) inhabit a middle ground between gas giants like the planet Jupiter (far left) and stars like our sun (far right).

In fact, Rutledge and his colleagues pursued this particular brown dwarf precisely because of its unique size. In 1998, Lars Bildsten of the University of California at Santa Barbara, Gibor Basri, Rutledge and Eduardo Martin of Caltech decided to observe the brown dwarf with the Chandra X-ray Observatory, which is designed to help scientists "see" X-rays -- an extremely high-energy form of radiation -- emanating from celestial bodies.

Scientists know that X-ray flares are produced by even the smallest stars. Such massive bursts of X-ray energy are released when loops associated with the objects magnetic field grow, peek out from the suns surface, super-heat convecting plasma sheets, and eventually dissipate high-energy radiation into space, said Rutledge.

But until recently, many believed that X-ray flaring activity was reserved for true stars only. When Chandra picked up X-ray emissions from the lightweight brown dwarf LP 944-20, scientists realized they might have to completely rethink their theory.

"We thought we understood the flaring activity," said Rutledge. "It should have stopped at objects which are less massive than our sun, but still stars. So heres an object from which we absolutely should not see anything!"

Since this is only the first example of a brown-dwarf flare, many questions remain as to how astronomers will eventually be able to categorize the activity of these sub-stellar objects.

"Eventually, at smaller and smaller [masses] these flares have got to stop," Rutledge explained. "But how? Why? -- We dont yet know."

To help get them closer to an understanding of brown dwarfs, the astronomers have already planned a number of future X-ray observations. For now, their initial findings will be published in the July 20 issue of Astrophysical Journal Letters.