http://www.cnn.com/2003/TECH/space/09/10/blackhole.music.reut/index.html
Black hole hums deepest note ever detected
Wednesday, September 10, 2003 Posted: 1:51 PM EDT (1751 GMT)
WASHINGTON, Sept 9 (Reuters) -- Big black holes sing bass. One particularly
monstrous black hole has probably been humming B flat for billions of
years, but at a pitch no human could hear, let alone sing, astronomers said
this week.
"The intensity of the sound is comparable to human speech," said Andrew
Fabian of the Institute of Astronomy at Cambridge, England. But the pitch
of the sound is about 57 octaves below middle C, roughly the middle of a
standard piano keyboard.
This is far, far deeper than humans can hear, the researchers said, and
they believe it is the deepest note ever detected in the universe.
The sound waves are emanating from the Perseus Cluster, a giant clump of
galaxies some 250 million light-years from Earth. A light-year is about 6
trillion miles (10 trillion km), the distance light travels in a year.
Fabian and his colleagues used NASA's orbiting Chandra X-Ray Observatory to
investigate X-rays coming from the cluster's heart.
Researchers presumed that a supermassive black hole, with perhaps 2.5
billion times the mass of our sun, lay there, and the activity around the
center bolstered this assumption.
Black holes are powerful matter-sucking drains in space, and astronomers
believe most galaxies, including our own Milky Way, may contain black holes
at their centers.
Black holes have not been directly observed, because their gravitational
pull is so strong that nothing, not even light, can escape it.
Making waves
So researchers have concentrated on what happens around the edges of black
holes, just before matter is pulled in.
When scientists trained the Chandra observatory on the center of Perseus
last year, they saw concentric ripples in the cosmic gas that fills the
space between the galaxies in the cluster.
"We're dealing with enormous scales here," Fabian said in a telephone
interview. "The size of these ripples is 30,000 light-years."
Fabian said the ripples were caused by the rhythmic squeezing and heating
of the cosmic gas by the intense gravitational pressure of the jumble of
galaxies packed together in the cluster.
As the black hole pulls material in, he said, it also creates jets of
material shooting out above and below it, and it is these powerful jets
that create the pressure that creates the sound waves.
To scientists, he said, pressure ripples equate to sound waves. By
calculating how far apart the ripples were, and how fast sound might travel
there, the team of researchers determined the musical note of the sound.
Fabian said the notion of singing black holes might well be extrapolated to
other galaxies, but not necessarily to the Milky Way.
Chandra has looked at X-ray emissions from the Milky Way's center, and
astronomers believe there is a black hole there, but because it is a young,
rambunctious galaxy with lots of activity at its heart, this may interfere
with any note our black hole might sing, Fabian said.
