Black holes are thought to form when stars of sufficient size collapse, creating a force so strong that nothing can oppose it. The result is a region of space with infinite density and a gravitational field so strong that nothing, not even light, can escape.
The idea that no known force can oppose the collapse of a large star sits uncomfortably with many physicists. Einstein believed that black holes could not form because the angular momentum of the star would eventually become high enough to stabilize a collapse.
Others say that our inability to find a force that opposes collapse says more about our limited understanding of physics than about the existence of black holes.
The current thinking is that any star three or four times bigger than the sun ought to form a black hole in a supernova at the end of its life. Anything smaller than that, and the degeneracy pressure of neutrons, which prevents neutrons from being squashed too closely together, can successfully oppose the collapse. Hence the formation of neutron stars.
Now Ilya Royzen from the P.N. Lebedev Physical Institute of the Russian Academy of Sciences, in Moscow, has put his finger on an even more powerful force at work in supernovas.
He says that quantum chromodynamics predicts that when a collapse overcomes the pressure of neutron degeneracy, another effect comes into play: matter undergoes a phase change.
This change is from a hadronic form to a so-called subhadronic form, which is very different to ordinary matter. In subhadronic form, space is essentially empty. So the phase change creates a sudden reduction in pressure, allowing any ordinary matter in the star to implode into this new vacuum. The result is a massive increase in temperature of this matter to 100 million electron volts or so, creating what Royzen calls a “burning wall” within the supernova.
He says that it is this “burning wall that stops the formation of a black hole during a supernova of stars up to about four times the mass of the sun, not just the degeneracy pressure of neutrons.”
Now 100 million electron volts is several orders of magnitude more energy than any theory of supernovas has predicted so far. And that’s interesting because it ought to produce very powerful gamma rays.
Strangely enough, the most powerful gamma rays are several orders of magnitude more powerful than can be explained by existing theories of supernovas.
As Royzen says, it’s hard to resist making the link. If it stands up, he may have put his finger on the mechanism that finally explains the most powerful gamma-ray bursts in the universe and one of the great modern-day mysteries of astrophysics.
Ref: arxiv.org/abs/0906.1929: QCD Against Black Holes?