March 2002 - Astronomers find shortest period binary system
at the Mullard Space Science Laboratory
(MSSL) together with a colleague in Finland have discovered a stellar binary
system in which the two stars are orbiting around each other every 5 minutes.
A seperate group in Rome also made this discovery independently at the same
time. This object sets the record as the fastest known binary and beats the
previous record-holder by 5 minutes.
astronomers found this object using the Nordic Optical Telescope in the Canary Islands.
Before they went there they knew the approximate position in the sky of
an X-ray source which varied in brightness on a timescale of 5 minutes.
They managed to locate one faint star in the same position in optical
light which showed small variations in its brightness on exactly the same
timescale. They came to the conclusion that this 5 minute modulation is
the time that it took two stars to orbit each other. The two stars are
both thought to be very dense, compact, old stars called white dwarfs.
They are extremely close to each other - about 1/5 of the distance to
picture no longer available
time, the two stars will gradually move closer together and form one star
as gravitational radiation is released. If the combined mass of the two stars
is high enough, the merger will result in a supernovae. Currently it is not
clear if the mass will be high enough. Such a merger is expected to occur
in around a 100,000 years.
period binary systems of the sort detected by the group at MSSL are expected
to be the strongest sources of constant gravitational radiation in the night
sky. They will easily be detectable using a satellite called LISA which the European Space Agency
and NASA plan to launch in 2010. The MSSL group is setting out to find more
of these elusive objects.
Further details can be found in the paper by Ramsay et al 2002 and
also the paper by Israel et al 2002.
"Dashing Dwarfs" by Cameron Slayden. Reprinted with permission
from Science 295:1997 (15 March 2002), Stellar Pair Whirls in a 5-minute
dash, L Irion. Copyright 2002 American
Association for the Advancement of Science.
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