Featured Research

from universities, journals, and other organizations

First X-Ray From Brown Dwarf Observed

Date:
July 11, 2000
Source:
University Of California, Santa Barbara
Summary:
Surprised scientists made provocative observations of an X-ray flare from a celestial object called a brown dwarf -- the first ever seen from such an object -- giving them strong hints of the tangled magnetic fields that may exist inside, according to an article to be published in the July 20 issue of the Astrophysical Journal Letters.

"It was as if we were searching for a dim bulb and instead found a bright flash of light." -- Lars Bildsten, professor, University of California, Santa Barbara

Surprised scientists made provocative observations of an X-ray flare from a celestial object called a brown dwarf -- the first ever seen from such an object -- giving them strong hints of the tangled magnetic fields that may exist inside, according to an article to be published in the July 20 issue of the Astrophysical Journal Letters.

"We were most surprised by the fact that it was a flare," said Lars Bildsten, co-author and professor of physics at the Institute for Theoretical Physics at the University of California, Santa Barbara.

"At best we expected a few photons every hour," said Bildsten. "Instead, we saw nothing for nine hours and then a bright flare that lasted nearly two hours. If the observation had been shorter, we would have nothing to report."

"We were shocked," said Robert Rutledge, of the California Institute of Technology in Pasadena, and lead author of the paper. "We didn't expect to see flaring from such a lightweight object. This is really the 'mouse that roared.'"

This first X-ray flare ever seen from a brown dwarf, or failed star, was detected by NASA's Chandra X-ray Observatory, the telescope that was launched nearly a year ago. The bright X-ray flare has implications for understanding the explosive activity and origin of magnetic fields of extremely low mass stars, according to the team of four who made the discovery.

"It was as if we were searching for a dim bulb and instead found a bright flash of light," said Bildsten.

"Less massive than stars but more massive than planets, brown dwarfs were long assumed to be rare," explained principal investigator Gibor Basri in the April issue of Scientific American. "New sky surveys, however, show that the objects may be as common as stars."

Chandra detected no X-rays at all from the brown dwarf known as "LP 944-20" for the first nine hours of a twelve hour observation, then the source flared dramatically before it faded away over the next two hours. The energy emitted in the brown dwarf flare was comparable to a small solar flare and 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," said Eduardo Martin, of Caltech, also a member of the team.

Professor Gibor Basri of the University of California, Berkeley, the principal investigator for this observation, speculated that "the flare could have its 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."

Basri, an expert in brown dwarfs wrote an article describing them in the April issue of Scientific American. In that article he explains: "A brown dwarf is a failed star. A star shines because of the thermonuclear reactions in its core, which release enormous amounts of energy by fusing hydrogen into helium. For the fusion reactions to occur, though, the temperature in the star's core must reach at least three million kelvins. And because core temperature rises with gravitational pressure, the star must have a minimum mass: about 75 times the mass of the planet Jupiter, or about 7 percent of the mass of our sun. A brown dwarf just misses that mark -- it is heavier than a gas-giant planet but not quite massive enough to be a star."

The brown dwarf, named LP 944-20, is about 500 million years old and has a mass that is about 60 times that of Jupiter, or 6 percent of the sun's mass. Its diameter is one-tenth that of the sun and 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.

The researchers explained that the absence of X-rays from LP 944-20 during the non-flaring period is in itself a significant result. It sets the lowest limit on steady X-ray power produced by a brown dwarf, and shows that million degree Celsius upper atmospheres, or coronas, cease to exist as the surface temperature of a brown dwarf cools below about 2500 degrees Celsius.

"This is an important confirmation of the trend that hot gas in the atmospheres of lower mass stars is produced only in flares," said Bildsten.

Since 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 -- at a rate of a few inches per year. They are very dim -- one hundredth of 1 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 are intermediate between normal stars and giant planets.

###

The 12-hour observation of brown dwarf LP 944-20 was made on December 15, 1999, using the Advanced CCD Imaging Spectrometer (ACIS). The ACIS instrument was built for NASA by the Massachusetts Institute of Technology, Cambridge University, and Pennsylvania State University, University Park. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program. TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge, Mass.

Editors: Images associated with this release are available on the Internet at: http://chandra.harvard.edu and http://chandra.nasa.gov

High resolution digital versions of the X-ray image (JPG, 300 dpi TIFF) are also available at the Internet sites listed above.

"The Discovery of Brown Dwarfs," with images, featured in the April 2000 issue of Scientific American is available on the Internet at: http://www.sciam.com/2000/0400issue/0400basri.html


Story Source:

The above story is based on materials provided by University Of California, Santa Barbara. Note: Materials may be edited for content and length.


Cite This Page:

University Of California, Santa Barbara. "First X-Ray From Brown Dwarf Observed." ScienceDaily. ScienceDaily, 11 July 2000. <www.sciencedaily.com/releases/2000/07/000711073612.htm>.
University Of California, Santa Barbara. (2000, July 11). First X-Ray From Brown Dwarf Observed. ScienceDaily. Retrieved September 30, 2014 from www.sciencedaily.com/releases/2000/07/000711073612.htm
University Of California, Santa Barbara. "First X-Ray From Brown Dwarf Observed." ScienceDaily. www.sciencedaily.com/releases/2000/07/000711073612.htm (accessed September 30, 2014).

Share This



More Space & Time News

Tuesday, September 30, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

The Water You Drink Might Be Older Than The Sun

The Water You Drink Might Be Older Than The Sun

Newsy (Sep. 27, 2014) Researchers at the University of Michigan simulated the birth of planets and our sun to determine whether water in the solar system predates the sun. Video provided by Newsy
Powered by NewsLook.com
First Woman Cosmonaut in 17 Years Blasts Off for ISS

First Woman Cosmonaut in 17 Years Blasts Off for ISS

AFP (Sep. 26, 2014) A Russian Soyuz spacecraft carrying an American astronaut and two Russian cosmonauts, including the first woman cosmonaut in 17 years, blasted off on schedule Friday. Duration: 00:35 Video provided by AFP
Powered by NewsLook.com
Water Discovery On Small Planet Could Be Key To Earth 2.0

Water Discovery On Small Planet Could Be Key To Earth 2.0

Newsy (Sep. 25, 2014) Scientists have discovered traces of water in the atmosphere of a distant, Neptune-sized planet. Video provided by Newsy
Powered by NewsLook.com
Raw: US-Russian Crew Lifts Off for Space Station

Raw: US-Russian Crew Lifts Off for Space Station

AP (Sep. 25, 2014) A U.S.-Russian space crew has blasted off successfully for the International Space Station. The Russian Soyuz-TMA14M spacecraft lifted off from the Russian-leased Baikonur launch facility in Kazakhstan. (Sept. 25) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins