brown_dwarf_power_010314 While pursuing a cosmic event that experts said almost certainly did not exist, a group of 13 students made the first detection ever of radio waves coming from a cool, failed star known as a brown dwarf.
The radio emissions spiked up to 10,000 times stronger than what astronomers thought possible, indicating an intense flare of energy that may be similar to flares on the Sun, researchers said. The brown dwarf, called LP 944-20, was found to emit radio waves constantly, with intermittent flares that last for hours.
Researchers said the discovery, which is discussed in the March 15 issue of the journal Nature, might force a rethinking of what constitutes a brown dwarf and what goes on inside the enigmatic objects.
"We once had a clear definition.... The new findings may indicate that the reality is more complex than we thought."
"Many astronomers are surprised at this discovery, because they didn't expect such strong radio emission from this object," said Shri Kulkarni, a Caltech professor who in 1995 participated in finding the first confirmed brown dwarf. Kulkarni advised one of the 13 students who made the discovery during a summer project.
Adding to the mystery
Brown dwarfs are mysterious objects that bridge a fuzzy definition gap between planets and real stars. Larger even than massive Jupiter, brown dwarfs are classified as small, dim stars that do not have enough mass to jump-start thermonuclear fusion, which converts hydrogen to helium and powers full-blown stars.
Because they give off no more than a faint red glow (by fusing the element deuterium) brown dwarfs are hard to find. But as
more have been spotted in recent years, scientists have speculated that there may be as many brown dwarfs in our galaxy as there are stars. But they still know little about them.The temper of LP 944-20 had previously been
captured in X-rays, a finding announced in July 2000. The new discovery of strong radio emissions from the same object only adds to the mystery of brown dwarfs, researchers said."It is not surprising that LP 944-20 has flares, but it is surprising that they are so bright in the radio [wavelengths]," said the University of Hawaii's Eduardo Martin, who was involved in the previous X-ray findings. "The result is significant in telling us that brown dwarfs break the rules of stellar astronomy."
Brown dwarfs are known to break another rule by rotating faster than most normal stars, Martin said.
The radio signal
In regular stars, radio and X-ray emissions are related processes. Radio waves are created by the interaction of electrons with a star's magnetic force, which sends magnetic loops out through hot plasma above the surface, says Arnold O. Benz of the University of Zurich's Institute of Astronomy. Writing in an accompanying analysis in Nature, Benz explains that these electrons follow a star's magnetic field lines down into the cooler surface, where they heat gases and generate X-rays.
Researchers have measured how strong a star's radio emissions typically are in relation to its X-ray emissions. Confounding predictions, the brown dwarf LP 944-20 emits radio waves much more intensely and energetically than would be expected, based on its known X-ray emissions.
Benz said the discovery points to the possibility that brown dwarfs might emit radio waves via a completely different process than normal stars. This possibility further blurs the
ill-defined boundaries between planets, brown dwarfs and real stars. "We once had a clear definition," Benz told SPACE.com. "Stars burn deuterium and hydrogen, brown dwarfs only deuterium, planets nothing. The new findings may indicate that the reality is more complex than we thought."
Students had "almost nothing to lose"
Located in the constellation Fornax in the southern skies, LP 944-20 is relatively nearby -- roughly 15 light-years from Earth. The brown dwarf is about 500 million years old and has a mass about 60 times that of Jupiter, or 6 percent that of the Sun.
A group of students on a National Science Foundation summer program at the Very Large Array near Socorro, New Mexico, decided to make the brown dwarf their project. Though their research told them the object would be undetectable in radio waves, "we decided to try it anyway," said Edo Berger, a Caltech graduate student who led the group.
"What is so cool is that this is research that probably nobody else would have tried to do because of its low chance of success," said Kate Becker, a student from Oberlin College in Ohio who also participated. "That made it ideal for summer students -- we had almost nothing to lose."
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