Apr 20, 2007
Brown dwarfs are a type of "failed" star
A class of "failed" star called a brown dwarf emits beams of radiation that are thousands of times brighter than any released by the Sun.
The brown dwarfs are behaving like an altogether different and exotic cosmic object called a pulsar.
Pulsars are rotating neutron stars that emit a flashing radio signal.
When the rotating beams sweep Earth, astronomers detect the radio pulse, which has been likened to the rotating beacon of a lighthouse.
Pulsars are created when a massive star explodes in a supernova and its core collapses into a rapidly spinning neutron star.
Brown dwarfs, on the other hand, are stellar also-rans which lack the necessary mass to kick-start nuclear fusion reactions in their cores.
Greg Hallinan from the National University of Ireland in Galway and his colleagues used the Very Large Array radio telescope in New Mexico to observe a very cool, rapidly rotating brown dwarf called TVLM 513-46546.
A bright flash from the brown dwarf was observed roughly every two hours.
All the planets with a magnetic field, including Earth, have bright radio emission from their magnetic polar regions.
Brown dwarfs are thought to generate their emission in a similar way to pulsars. But here, the emission is many times brighter than that from planets. The radio waves are produced above the object's magnetic poles.
This radio emission requires these brown dwarfs to possess magnetic fields as powerful as those detected at the most magnetically active stars.
The periodic pulses detected from brown dwarfs are very similar to those observed from pulsars. But the whole system is on a much slower and smaller scale, so it is easier for astronomers to decipher what is going on.
How pulsars produce their radiation has been a problem in astrophysics for 40 years.
This is because we have little understanding of how hot, electrified gas, or plasma, behaves in the extreme conditions present at a pulsar.
Brown dwarfs are now the second class of stellar object known to produce persistent levels of extremely bright, "coherent" radiation.
Moreover, this radio signal manifests itself as periodic pulses. However, in the case of brown dwarfs, both the source conditions and the emission mechanism are reasonably well understood.
For some time, scientists have wondered if there were similarities between this type of emission and the periodic radio beams from pulsars. Observations of TVLM 513-46546 could provide the first direct evidence for such a link.
Dr Hallinan said: "Our research shows that these objects can be fascinating and dynamic systems, and may be the key to unlocking this long-standing mystery of how pulsars produce radio emissions.
"It looks like brown dwarfs are the missing step between the radio emissions we see generated at Jupiter and those we observe from pulsars".
The National University of Ireland astrophysicist presented details of his work at the Royal Astronomical Society's National Astronomy Meeting in Preston.