Chandra Spots First Brown Dwarf Flare
By Discovery.com 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.