Black Holes: Too Uniform for Chance?

From: Ndunlks@aol.com
Date: Wed, 11 Jun 1997 23:17:36 -0400 (EDT)
Subject: Black Holes: Too Uniform for Chance ?

.c The Associated Press

WINSTON-SALEM, N.C. (AP) - Nature may make black holes with cookie-cutter precision, according to an astronomer who has found such uniformity in these mysterious objects that he suggests their size may be controlled by some basic law of physics.

Yale University astronomer Charles Bailyn said Tuesday that measurements of the mass of the known stellar black holes show that all but one of them are seven times the size of the sun.

``Nature is stamping out these things at seven solar masses, for some reason,'' he said. ``What you would expect is a broad distribution in sizes. That's what makes this such a surprising result.''

Bailyn gave a report on his black-hole findings at a national meeting of the American Astronomical Society.

All the black holes analyzed by the Yale team were formed when stars burned up their nuclear fuel and then exploded as supernovas.

Bailyn said the supernovas were all more than eight solar masses, and some perhaps twice that size, at the moment of explosion. But after the debris cleared from the blowup, they settled into black holes seven times the mass of the sun.

``Seven solar masses seems to be some sort of magic number for these things,'' he said. ``Something about the collapse of a star in a supernova explosion seems to favor retaining seven solar masses of matter in the black hole and blowing the rest of the star back into space.''

Bailyn and his team determined the size of all seven of the known stellar black holes and there was only one exception to the rule of seven. That one was about 14 solar masses.

The size of the black holes, said Bailyn, is too uniform to be a matter of chance and he suggested there could be some law of nature that results in the ``magic number.''

Stellar black holes are formed from remnants of a supernova. The dying star collapses into a single point of density that creates such a powerful gravitational field that nothing, not even light, can escape. Since it gives out no light it is invisible, giving the object its name.

Stellar black holes are much smaller than the supermassive black holes that are thought to be at the center of many galaxies.

Each of the stellar black holes is orbited by a companion star, usually several times the size of the sun. These stars are being swallowed, bit by bit, by the black hole. The forces are so severe that the normal spherical form of the companion star is warped, changing from a basketball shape to one more like a football.

Billions of tons of matter stream from the companion star constantly. As it approaches the center of black hole, the matter heats to millions of degrees and sends beams of X-rays streaming through the heavens.

Bailyn said that as the companion star is drawn inward, its orbit speeds up and some are now whipping around the black hole in two days or less.

The sizes of the black holes were determined by measuring the orbital speed and mass of the companion stars. Once this is established, Bailyn said, mathematical calculations make it possible to find the mass of the black hole.

Now, said Bailyn, astronomers need to figure out why most stellar black holes seem limited to seven times the mass of the sun.

``This new finding will send astrophysicists back to their supernova computer models to try to figure out why,'' he said.

AP-NY-06-10-97 1446EDT