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Black hole secrets revealed
Jan 13 '05
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SAN DIEGO, United States (AFP) - Black holes, the invisible celestial
bodies whose enormous gravitational pull sucks in everything around them, are
beginning to share some of their secrets.
Using the newest generation of satellite-mounted x-ray telescopes,
astrophysicists are starting to divine the shape and size of these mysterious
objects, whose gravitational pull appears to be the fundamental source of
energy at the heart of galaxies.
At the same time, their discoveries are producing new evidence for the
89-year-old theory of reletivity of legendary physicist Albert Einstein.
Black holes are created by an immense gravitational contraction of matter
after the universe's largest stars burn up their nuclear cores and explode as
supernovas.
As the star burns out, it forms a dark concentration of matter with a
diameter of maybe just 24 kilometers (14.5 miles) but a mass four times greater
than our own sun. The gravitational pull siphons up everything that passes
nearby.
Black holes are so dense that even light cannot escape, rendering them
invisible and only detectable by their effect on their environment.
As Einstein proposed in his 1916 theory of relativity, scientists can
detect black holes' attributes by the way their pull deforms the continuum of
space-time around them.
This pull is equally powerful on astronomers and astro-physicists, who
are reporting numerous potentially important discoveries about black holes at
the winter convention of the American Astronomical Society, taking place this
week in San Diego, California.
Harvard University astrophysicist Jon Miller and his colleagues report
that they have detected particles of gas literally "surfing on a wave of
space-time" around the black hole known as GRS 1915+105, situated 40,000
light-years from Earth in the constellation Aquila.
Their observations, made with the US space agency NASA's Rossi X-Ray
Timing Explorer, a satellite-based x-ray telescope, shows how the gravitational
force of black holes can "warp and drag the fabric of space-time" as Einstein
theorized, Miller said.
Another team of scientists led by the University of Maryland's Jane
Turner observed three clumps of super-heated gas particles orbiting a black
hole at 32,000 kilometers (19,000 miles) a second, about one-tenth the speed of
light.
Using the European Space Agency's XXM-Newton x-ray satellite, Turner's
team followed these bits of matter as they made a complete revolution around
the black hole.
"Knowing that, scientists can measure black hole mass and other
characteristics that have long eluded them," explained Turner.
Steinn Sigurdsson, Professor of Astronomy at Pennsylvania State
University, was to show the convention on Wednesday how giant black holes, like
those at the center of our own Milky Way, swallow up smaller black holes and
extremely dense neutron stars to become even more massive.
Using ultra-sophisticated computer modeling, Sigurdsson and his
colleagues estimated that they should be able to observe such events several
times a year.
They hope to do so via the joint NASA-European Space Agency LISA project,
involving three satellites to be launched in 2012. Equipped with laser
antennae, the satellites will detect waves of gravitational radiation unleashed
when a small black hole or neutron star falls into a giant black hole,
Sigurdsson explained in a paper at the conference.
Predicted by Einstein and moving at the speed of light, these ripples of
time-space have never been detected directly. The LISA project represents the
best chance of studying black hole absorption, Sigurdsson said.
� 2005 AFP
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