The nature of black holes has puzzled physicists for decades. But while the debate has fizzled in recent years, some new thinking is about to set it alight again.
Black holes are fundamentally a product of general relativity, which allows for a gravitational collapse so violent that no other force can oppose it. When that happens, the collapse continues until the density of matter becomes infinite and gravity becomes so strong so as to prevent even light from escaping. This generates an “event horizon”, a volume of space around the black in hole inside whihc events cannot affect an outside observer.
But perhaps there’s more to it than that, suggest Matt Visser at Victoria University of Wellington in New Zealand and pals who ask whether quantum processes can have an affect on the collapse of a star.
It’s fair to say that the consensus among astrophysicists is that quantum physics can be safely ignored when considering the collapse of a star. As Visser and co put it: “There is a widespread feeling in the general relativity community that semiclassical quantum back-reaction effects are always small, and never enough to significantly alter the classical picture of collapse to a black hole.”
But Visser and pals beg to differ. The standard thinking is that if an event horizon forms, then quantum field theory is well behaved there. But that makes the assumption that am event horizon will form.
Visser and co say this may not be a valid assumption and go on to show how the vacuum energy might stifle the formation of an event horizon.
What does this mean for black holes? What Visser and co end up with is something very similar to a black hole but without an event horizon–a black hole mimic, they say.
Debating the nature of black holes is a well trodden path. But what’s interesting is that numerous avenues of thought–from loop quantum gravity to abstract studies of the nature of horizons–are now hinting at something more subtle and interesting about the nature of star collapse.
Black holes might never be the same again.
Ref: arxiv.org/abs/0902.0346: Small, dark, and heavy: But is it a black hole?