March 29, 2005
In Lab's High-Speed Collisions, Things Just Vanish By KENNETH CHANG NY Times
http://www.nytimes.com/2005/03/29/science/29blac.html?pagewanted=print&position=
The bits and pieces flying out from the high-speed collisions of gold nuclei at Brookhaven National Laboratory on Long Island have not been behaving quite as physicists had expected.
According to one theoretical physicist, the collisions have even been creating a sort of tiny, short-lived black hole - very, very tiny and very, very short-lived. It lasts less than one-10,000,000,000,000,000,000,000th of a second.
And it's not even really a black hole.
The black holes known to astronomers form when a star (or something larger) collapses and the gravitational pull grows so powerful that nothing can escape, not even light.
The Brookhaven mini-black hole, if it existed, would have nothing to do with gravity. Brookhaven's Relativistic Heavy Ion Collider, RHIC (pronounced rick) for short, accelerates gold nuclei - atoms stripped of their surrounding clouds of electrons - to 99.995 percent of the speed of light and then slams them together, head-on.
The calculations of Dr. Horatiu Nastase, a professor of physics at Brown, suggest that in the trillion-degree fireball of a collision, the so-called "strong force" that holds protons and neutrons together, would briefly create a black-hole-like vortex that swallowed part of the gold.
"The reason it acts like a black hole is because it eats up stuff and it only gives out radiation," Dr. Nastase said.
He added that even if his supposition was correct, these black holes posed no danger to Brookhaven or the planet. "It would be very hard to create anything bigger," he said. That is because black holes do not last forever. Dr. Stephen W. Hawking of Cambridge University showed that they gradually burp out what they swallow. And a tiny black hole spews energy far faster than it swallows and will evaporate almost instantly into nothing.
In a normal black hole, the energy comes back out as photons, particles of light, what is called Hawking radiation. In a strong force mini-black hole, the radiation would come out as particles known as pions. Because of the differences between gravity and the strong force, a strong force black hole would inevitably fall apart, Dr. Nastase said. He has written a scientific paper describing his ideas, available at arxiv.org, but he has not yet submitted to a journal for publication.
Before Brookhaven began its gold collision experiments in 2000, it issued assurances that the experiment could not accidentally create a black hole that would destroy the earth. Laboratory officials say that is still the case.
In a message posted on Brookhaven's Web site, Dr. Dmitri Kharzeev, a theoretical physicist at Brookhaven, wrote: "This imaginary, mathematical black hole that Horatiu compares to the RHIC fireball is completely different from a black hole in the real universe; in particular, it cannot grow by gobbling up matter. In other words, and because the amount of matter created at RHIC is so tiny, RHIC does not, and cannot possibly, produce a true, star-swallowing black hole."
The collisions of gold nuclei produce matter as it existed shortly after the Big Bang. In the everyday universe, protons and neutrons in atomic nuclei are made of smaller particles known as quarks that are held together by the strong force, and because the strong force is so strong, it is ordinarily impossible to pull out a single quark.
But physicists expected that at ultrahot temperatures the bindings holding the quarks together would loosen and dissolve into a new state of matter, the quark-gluon plasma. (Gluons are the particles that carry the strong force, just as photons are the particles that carry the electromagnetic force.)
Five years later, however, physicists are still holding off from claiming they have made a quark-gluon plasma. That is in part because the result of the collisions looks more like a liquid than a gaseous plasma.
"It doesn't resemble what our naïve expectations for quark-gluon plasma were," said Dr. William A. Zajc, a professor of physics at Columbia and the spokesman for one of the detectors on the collider.
The equations describing the quantum mechanics of the strong force are particularly difficult to solve, and it turns out that turning to mathematical models that described the collisions in terms of a plasma "was really looking under the lamppost because it was easy to do the calculations," Dr. Zajc said.
So theorists are now looking for other ways to attack the problem. Dr. Nastase used a technique that recasts the equations into a form that resembles general relativity and gravity, which, while hardly simple, have been solved for some cases. But while the equations are similar, Dr. Zajc said, "This is a mathematical mapping, and these are not real black holes."
The scientists working on the experiment hope to figure out by summer a more definitive answer of what they actually produced at RHIC.
================================ George Antunes, Political Science Dept University of Houston; Houston, TX 77204 Voice: 713-743-3923 Fax: 713-743-3927 antunes at uh dot edu
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