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Chandra Spots First Brown Dwarf Flare
By News
June 12, 2000 --- The first flare ever seen from a brown dwarf was detected by NASA's Chandra X-ray Observatory.  The bright X-ray flare has implications for understanding the explosive activity and origin of magnetic fields of extremely low-mass stars, according to a NASA news release, said Dr. Robert Ruthedge of the California Institute of Technology in Pasadena, the lead author on the discovery, which will be described in the July 20 issue of Astrophysical Journal Letters.  "We didn't expect to see flaring from such a lightweight object.  This is really the 'mouse that roared.'"
The energy emitted in the brown dwarf flare was comparable to a small solar flare, and was a billion times greater than observed X-ray flares from Jupiter.  The flaring energy is believed to come from a twisted magnetic field.
"This is the strongest evidence yet that brown dwarfs and possibly young giant planets have magnetic fields, and that a large amount of energy can be released in a flare," Dr. Eduardo Martic, also of Caltech and a member of the team, said in the news release.
Bibor Basri of the University of California, Berkeley, the principal investigator for this observation, speculated that the flare " could have it's origin in the turbulent magnetized hot material beneath the surface of the brown dwarf.  A sub-surface flare could heat the atmosphere, allowing currents to flow and give rise to the X-ray flare --- like a stroke of lightning."
LP 944-20, essentially a failed star is about 500 million years old and has a mass that is about 60 times that of Jupiter, or 6 percent that of the sun.  Located in the constellation Fornax in the southern skies, LP 944-20 is one of the best-studied brown dwarfs because it is only 16 light-years from Earth.
Brown dwarfs have too little mass to sustain significant nuclear reactions in their cores.  Their primary source of energy is the release of gravitational energy as they slowly contract.  They are very dim -- less than a tenth of a percent as luminous as the sun -- and of great interest to astronomers because they are poorly understood and probably a very common class of objects that bridge the gap between normal stars and giant planets.


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