More sound science to think and ponder:

Black Holes Sing Bass, But Humans Can't Hear Them
Tue Sep 9, 1:55 PM ET

By Deborah Zabarenko

WASHINGTON (Reuters) - Big black holes sing bass.


Reuters Photo












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 on Tuesday.


"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 is 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, the distance light travels in a year.


Fabian and his colleagues used NASA (news - web sites)'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.


SOUND 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.