Date: 14 March 1995
From: Ron Baalke <BAALKE@KELVIN.JPL.NASA.GOV>
Subject: Possible Quasar Found in Milky Way Galaxy
ASTRONOMERS DISCOVER POSSIBLE QUASAR IN MILKY WAY GALAXY
The strange behavior of a newly discovered star in the Milky Way galaxy
as it spewed out huge jets of material at nearly the speed of light has
led an international team of radio astronomers to believe it may be a
black hole or neutron star powering a miniature quasar.
The star, identified as GRO J1655-40, was discovered using NASA's Gamma
Ray Observatory on July 27, 1994, when it underwent such a strong
outburst of x-rays that it quickly became the strongest x-ray source in
the sky, said Jet Propulsion Laboratory astronomer Dr. Robert Preston,
a member of the observing team which began tracking the object shortly
after its discovery.
"The star exhibited some exotic behavior," Preston said, "ejecting
material at 80 percent of the speed of light just like very powerful
quasars. This suggests that the object is likely to be powered by a
black hole or neutron star."
Black holes are thought to occur at the end of the lifetime of a
massive star, when the outward pressure of the star's diminishing
radiation can no longer prevent the gravitational collapse of the star
into a vanishingly small volume. Quasars are believed to contain
enormous black holes with masses of up to billions of times that of the
Sun. A neutron star is a less dense form of a collapsed old star, but
still has a density of more than a billion tons per teaspoon of
material.
The discovery represents only the second time that such an object has
been found in Earth's own galactic neighborhood. The observations were
made possible by a technique called interferometry, in which several
radio telescopes are used simultaneously to synthesize one enormous
telescope.
The extremely energetic star was estimated to be about 12,000 light-
years from Earth, or about 15 percent of the way across the Milky Way
galaxy, said Preston, whose findings appeared in this week's issue of
the science journal Nature.
The team believes that the collapsed star -- observed in the radio
portion of the electromagnetic spectrum -- is not a single star but
rather two stars in orbit about each other. They speculate that
material may have been drawn off one of the stars to form a disc that
spiraled into the other star, which is probably a black hole or
neutron star.
Their radio observations, surprisingly, revealed that the ejection of
matter from the star did not start until 12 days after the beginning
of the violent x-ray outburst.
"The enormous outburst could be caused by an unusually large piece of
the companion star falling onto the compact star, with the subsequent
expansion of the jets of matter being ejected perpendicularly from the
center of the disc," Preston said. "The influx of material was so
great during the x-ray outburst that it may have disrupted the
production of jets, thus causing the observed delay in the formation
of jets until the flow of material had diminished."
The fact that radio jets did not emerge until x-ray emissions had
subsided may be an important clue to the nature of jet production, not
only in similar objects but also in the much more luminous and massive
objects found in distant quasars at the edge of the universe, the team
reported.
"Since quasars are found at distances of up to almost a million times
farther away than this x-ray star, astronomers now have an opportunity
to study a similar process in much greater detail," Preston and his
colleagues said.
The team of radio astronomers reporting this discovery were from the
Jet Propulsion Laboratory and several other institutions in Australia
and South Africa. Their observations were made using an array of radio
telescopes located at various sites across the world, including
telescopes at NASA's Deep Space Network in both California and
Australia.
The research was sponsored in part by the Astrophysics Division of
NASA's Office of Space Science, Washington, D.C.
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- T o d d E. V a n H o o s e a r -
``'''vanhoose@lalaland.cl.msu.edu - vanhoose@msu.edu - vanhoose@lalaland.cl.msu.edu
(._.) Michigan State University - East Lansing, MI USA
(_) Computer Laboratory - Department of Communication
`---' <A HREF="http://lalaland.cl.msu.edu/~vanhoose/">My Home Page</A>
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