Miércoles 13 de Febrero de 2002, Ip nº 11

Is black hole theory full of hot air?
Por Richard Stenger

Arguing that black holes are riddled with contradictions, astronomers have devised what they consider a more plausible destiny for imploding stars.

Taking into account quantum physics, two U.S scientists suggest that giant dying stars transform themselves into what they call gravastars, shells of extremely dense matter with exotic space inside.

The hypotheses could address some perplexing anomalies in black holes, while at the same time account for indirect observations that seem to support their existence, the astronomers say.

According to conventional theory, some giant stars near the end of their lives explode into supernovas, leaving behind cores so dense that they collapse into a "singularity," or point of infinite density, otherwise known as a black hole.

The dark monster would possess an "event horizon," or boundary beyond which time ceases and neither light nor matter escapes. Inside, the laws of known physics break down.

Despite widespread approval of the theory for decades, Emil Mottola of the Los Alamos National Laboratory in New Mexico and Pawel Mazur of the University of South Carolina are not convinced.

Black holes were first conceived in the early 1900s, long before the discovery of quantum physics, a revolutionary scientific field that describes the nature of many fundamental particles and forces.

The first black hole proponents were ignorant of quantum fluctuations in the universe that affect everything from light particles to gravity, Mottola and Mazur observed.

"We are usually not aware of the quantum medium we are immersed in," Mottola writes in New Scientist, "like a fish in a calm pond who is not aware of all the incessant jiggling of water molecules."

Without quantum mechanics, the early theorists made crucial mistakes in envisioning black holes and their relationship with space and time, the two say.

As a consequence, astronomers have been forced to face bizarre paradoxes spawned by black hole theory.

For example, light photons would gain an infinite amount of energy when they reach an event horizon, according to classical theorists. But they ignore the gravitational effects of this unthinkable amount of energy.

Mottola and Mazur think they have a better explanation for what happens to a collapsing star.

Before a black hole could form, quantum effects would change space-time around an imploding giant, kicking off a radical phase transition akin to when liquid water becomes ice.

The shift to a new state would lead to the formation of an exotic new object, the gravastar, a condensed bubble enveloped by a thin spherical shell of gravitational energy.

In a paper submitted to Physical Review Letters, Mottola and Mazur argue that gravastars are consistent with classical laws of physics but do not have embarrassing inconsistencies as do black holes.

Moreover, from Earth, they would appear much the same as classical black holes.

Therefore, those chaotic dense hot spots throughout the universe that astronomers consider indirect proof of black holes could just as well support the existence of gravastars, they say.

Mottola and Mazur hope the gravastar will shed light on even the deepest mysteries of the universe. The weighty object could explain intense gamma ray bursts from the distant universe.

More boldly, they suggest the entire cosmos could itself be trapped inside a giant gravastar.

Short of borrowing the brain of Albert Einstein, how could anyone know if gravastars really are those turbulent cosmic whirlpools that gobble up energy and matter?

Astronomers call the work of Mottola and Mazur everything from "outstandingly brilliant" to "unlikely." Perhaps it will take decades or longer for anyone to know really.


  22/01/2002. CNN.