fossil_digger Report This Comment Date: December 02, 2008 03:18AM
On 12 February 2006, amateur astronomers reported that a faint star in the
constellation of ********* had suddenly become clearly visible in the night sky
without the aid of a telescope. Records show that this so-called recurrent nova,
RS ******* , has previously reached this level of brightness five times in the
last 108 years, most recently in 1985. The latest explosion has been observed in
unprecedented detail by an armada of space- and ground-based telescopes. is just
over 5,000 light years away from Earth. It consists of a white dwarf star (the
super-dense core of a star, about the size of the Earth, that has reached the
end of its main hydrogen-burning phase of evolution and shed its outer layers)
in close orbit with a much larger red giant star. The two stars are so close
together that hydrogen-rich gas from the outer layers of the red giant is
continuously pulled onto the dwarf by its high gravity. After around 20 years,
enough gas has been accredited that a runaway thermonuclear explosion occurs on
the white dwarf's surface. In less than a day, its energy output increases to
over 100,000 times that of the Sun, and the accredited gas (several times the
mass of the Earth) is ejected into space at speeds of several thousand km per
second. Five explosions such as this per century can only be explained if the
white dwarf is near the maximum mass it could have without collapsing to become
an even denser neutron star. What is also very unusual in RS Oph is that the red
giant is losing enormous amounts of gas in a wind that envelops the whole
system. As a result, the explosion on the white dwarf occurs "inside"
its companion's extended atmosphere and the ejected gas then slams into it at
very high speed. "In 2006, our first observations with the UK's MERLIN
system were made only four days after the outburst and showed the radio emission
to be much brighter than expected," added Dr. Eyres. "Since then it
has brightened, faded, then brightened again. With radio telescopes in Europe,
North America and Asia now monitoring the event very closely, this is our best
chance yet of understanding what is truly going on."
Credit:: David A. Hardy