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Radio Active Brown Dwarfs Are
A New Class Of Pulsar
04/24/2007
From
http://www.sciencedaily.com
(Additional comments below)
A study of brown dwarfs has revealed
that these "failed stars" can possess powerful magnetic fields and
emit lighthouse beams of radio waves thousands of times brighter
than any detected from the Sun. The brown dwarfs are behaving like
pulsars, one of the most exotic types of object in our Universe.
Gregg Hallinan of the National
University of Ireland, Galway, who is presenting the discovery at
the RAS National Astronomy Meeting in Preston on 18th April, said,
"Brown dwarfs tend to be seen as a bit boring - the cinders of the
galaxy. 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."
Since the discovery of pulsars forty years ago, astronomers have
been trying to understand how the rotating neutron stars produce
their flashing radio signals. Although there have been many attempts
to describe how they produce the extremely bright radio emissions,
the vast magnetic field strengths of pulsars and the relativistic
speeds involved make it extremely difficult to model. Brown dwarfs
are now the second class of stellar object observed to produce this
kind of powerful, amplified (coherent) radio signal at a persistent
level.
The emissions from the brown dwarfs appear to be very similar to
those observed from pulsars, but the whole system is on a much
slower and smaller scale, so it is much easier to decipher exactly
what is going on. Importantly, the mechanisms for producing the
radio emissions in brown dwarfs are well understood, as they are
almost identical to the processes that produce radio emissions from
planets.
Hallinan said, "It looks like brown dwarfs are the missing step
between the radio emissions we see generated at Jupiter and those we
observe from pulsars".
Jupiter's volcanic moon, Io, is a source of electrically charged gas
that is accelerated by the planet's magnetic field and causes
powerful radio laser, or maser, emissions. The radiation can be so
intense that Jupiter frequently outshines the Sun as a source of
energy at radio wavelengths.
For some time, scientists have thought that there may be
similarities between this type of maser emission and pulsars'
lighthouse-like beams of radio waves. Observations of the brown
dwarf, TVLM 513, using the Very Large Array (VLA) radio telescope,
may provide the first direct evidence for that link. The group
observed the brown dwarf over a period of 10 hours at two different
frequencies. In both cases, a bright flash was observed every 1.96
hours.
As yet, the processes controlling the radio flashes from TVLM 513
are still unclear. There is no evidence of a binary system, so
interaction of the magnetosphere with a stellar wind from a nearby
star seems an unlikely cause, nor is there any sign of an orbiting
planet that could produce a scenario like that of Jupiter and Io.
However, rapid rotation is also thought to be a source of electron
acceleration for a component of Jupiter's maser emission and this
may also be the main source of TVLM 513's radio flashes.
The group is now planning a large survey of all the known brown
dwarfs in the solar neighbourhood to find out how many are radio
sources and how many of those are pulsing. If a large fraction of
brown dwarfs are found to pulse, it could prove a key method of
detection for these elusive objects.
Note: This story has been adapted from a news release issued by
Royal Astronomical Society.
Original story
here
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