Chandra Observes First X-Ray Flare From A Brown Dwarf

By Keith Cowing
July 11, 2000
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X ray flare on a brown dwarf

The Chandra X Ray Observatory has detected an x-ray flare from LP 944-20, a brown dwarf star – the first ever recorded. Brown dwarfs are bodies smaller than our sun but many times the size of Jupiter. These observations will help astronomers further understand the nature of the magnetic fields that surround brown dwarfs and the manner in which hot gases are created and distributed within their atmospheres.

Brown dwarfs are often referred to as “failed suns” inasmuch as there was not enough matter present during their formation so as to initiate hydrogen fusion. Yet, at the same time, these objects are much more massive than Jupiter and produce energy as the result of gravity- induced contraction .

The flare’s observation were reported by researchers at the California Institute of Technology and the University of California Santa Barbara and will be published in the 20 July issue of Astrophysical Journal Letters.

According to a NASA press release, “LP 944-20 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. Its diameter is about one-tenth that of the sun and it has a rotation period of less than five hours. 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 exhibit characteristics that are sometimes similar to larger planets, and sometimes similar to small stars. In this case, the X-ray energy released is a similar to that released in a small solar flare yet is billion times greater than that which has been observed emanating from Jupiter.

According to a UCSB press release “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”. Researchers suspect that flares such as the one observed could originate in magnetized superheated material under the surface of a brown dwarf. According to the UCSB press release “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.”

These observations came as somewhat of a surprise to researchers. According to the UCSB press release, “We were shocked. We didn’t expect to see flaring from such a lightweight object. This is really the ‘mouse that roared.”

Related Links

° Chandra Detection of an X-ray Flare from the Brown Dwarf LP 944-20, Journal of Astrophysical Letters

° First X-ray from brown dwarf observed, University of California Santa Barbara

° Chandra captures flare from brown dwarf star, NASA MSFC

Background Information

° The Discovery of Brown Dwarfs, Scientific American

° Chandra website, NASA

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