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in Geoscience
doi:10.1038/nindia.2009.130 Published online 11 May 2009
An Indian theoretical astrophysicist who dared to show that there cannot be any 'black hole' a decade ago says he has a mathematical proof to back his claim.
"For a long time I tried to get this result published and now I succeeded," Abhas Mitra of the Bhabha Atomic Research Centre (BARC) in Mumbai, told Nature India. "This^{1} is evidence that the whole black hole paradigm is incorrect," Mitra said.
A black hole, as its proponents explain, results from gravitational collapse of a massive star. Its pull of gravity is so strong that nothing – not even light – can escape. It is surrounded by an imaginary boundary called the 'event horizon' that shuts everything within.
Nine years ago in a path-breaking peer-reviewed publication2 Mitra questioned the existence of black holes and thereby challenged British physicist Stephen Hawking, a key advocate of black holes. Since then, despite criticisms from mainstream scientists, he has been building more theoretical evidence to show black holes really do not exist.
In papers published then and in subsequent years, Mitra has been arguing that under Einstein's general theory of relativity, a spherically symmetric gravitational collapse of a star cannot result in a black hole as defined. According to Mitra's theory following is what should happen: during continued gravitational collapse of a massive star it must radiate away its entire mass energy in an 'asymptotic' manner, meaning that this process would go on and on indefinitely. At the same time, the radiation emitted by the collapsing star would get trapped by its ever increasing self-gravity. And a stage would be reached when the outward pressure of this trapped radiation would counter-balance the inward pull of gravity arresting the catastrophic collapse before any black hole or 'singularity' would actually form.
What then actually results, according to Mitra, is 'radiation pressure supported extremely relativistic star' — and not a black hole. "It is just a dense object, a hot ball of plasma, without an event horizon." He nicknamed these as 'Eternally Collapsing Objects' (ECOs) to signify the fact that they would keep shrinking steadily and indefinitely without ever achieving a black hole's infinitely small size. ECOs too look almost 'black' because their extreme surface gravity allows very little light or radiation to come out, he says. However, unlike a true black hole, ECOs have definite size, and objects sucked in can theoretically go back out, although with extreme difficulty.
Given that black holes have been the accepted scenario since Einstein, majority of mainstream scientists dismissed Mitra's original proposal of ECO, but support came from a few.
A group of American physicists, motivated by Mitra's work, confirmed3 in 2006 that the 'black hole candidates' that they observed met the criteria of Mitra's ECOs since they had intense magnetic fields that real black holes are not supposed to have. Mitra had felt vindicated earlier in July 2004, when Hawking at a conference in Dublin, Ireland, conceded that there is no black hole 'in the absolute sense.' Hawking had admitted that a black hole does not gobble up everything as he once theorised but keeps emitting radiation for a long time, exactly what Mitra showed in his paper2. And now, according to Mitra, the mathematical proof that he has just published is a confirmation that he had been right all along about ECOs.
The proof is highly mathematical but in simple terms he explains it as follows. "For the last 93 years the mass of a black hole appeared only as a (integration) constant in the so called Hilbert solution to the set of Einstein equations, appropriate for the spherical symmetry around the 'point mass'. And it has now been proved that the value of this constant is actually zero. What this means is that true black holes have to have zero gravitational mass and anything with a finite mass (M>0) is not a true black hole. In other words, the massive 'black hole candidates' detected by astronomers cannot be true black holes but only ECOs."
If Mitra (and the U.S. authors who found magnetised ECOs) are correct, astronomers should see dense, magnetic balls of plasma floating in the universe instead of the menacing black holes that gobble up everything that comes close.
According to Mitra detection of the so called 'black hole candidates' may be considered almost direct observational evidence of the controversial ECOs that he proposed. But astronomers say this is not a stringent test to resolve the dispute whether or not black holes exist. They hope that technology may become available within ten years to let them observe the 'event horizon', the authenticated signature of true black holes.
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