Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2000 July 13
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.

LP 944-20: A Failed Star Flares
Credit: R. Rutledge (Caltech) et al., NASA

Explanation: The tiny spot circled on the right actually represents a big astronomical discovery -- the first detected flare from a failed star. Failed stars, termed brown dwarfs in astronomers' parlance, are too low in mass to ignite nuclear hydrogen burning in their cores, yet still shine feebly as the energy from their gravitational collapse is converted to heat and light. In fact, the dim brown dwarf cataloged as LP944-20 is estimated to have only 6 percent the mass of the Sun (60 times the mass of Jupiter) and one-tenth the Sun's diameter. A mere 16 light-years distant in the southern constellation Fornax it is well studied, but this failed star recently startled astronomers by producing a flare visible at x-ray energies. The above Chandra X-ray Observatory images of the LP944-20 star field were recorded in December 1999. Showing nothing (left) for the first nine hours, the brown dwarf generated a significant x-ray flare during the final hours of the observation. How did a failed star produced such a high-energy flare? Magnetic fields twisted and broken by turbulent motions near the surface of the brown dwarf may be the culprit. Difficult to detect because they are otherwise faint, brown dwarf stars are believed to be common throughout the galaxy.

Tomorrow's picture: Crater On Ice

< | Archive | Index | Search | Calendar | Glossary | Education | About APOD | >

Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/GSFC
& Michigan Tech. U.