Some Black Holes May Pre-Date The Big Bang, Say Cosmologists
If the Universe expands and contracts in cycles of Big Bangs and Crunches, some black holes may survive from one era to the next, according to a new analysis
Black holes are regions of space in which gravity is so strong that nothing can escape, not even light. Conventionally, black holes form during a gravitational collapse, after a large supernova for example.
But there is another class of objects called primordial black holes that cosmologists think must have formed in a different way. These are essentially leftovers from the hugely dense ball of stuff from which the universe expanded, some parts of which must have been dense enough to form black holes.
These primordial black holes would then have been widely dispersed as the universe expanded.
Primordial black holes are very different beasts to the ones that form when stars die, in particular because they ought to be much smaller.
Although nobody has yet seen a primordial black hole, our knowledge of them comes from thinking about the processes that must have occurred shortly after the Big Bang.
In recent years, however, cosmologists have begun to think seriously about processes that occurred before the Big Bang. One idea, is that the Universe may eventually collapse leading to an endless cycle of Big Bangs and Crunches.
Today, Bernard Carr at Queen Mary University of London, UK, and Alan Coley at Dalhousie University in Canada, ask what might happen in such a universe in the moments before a crunch.
By some accounts, a Big Crunch generates a singularity that ought to cause everything in the Universe to merge. But Carr and Coley say that in some circumstances, black holes of a certain mass could avoid this fate and survive the crunch as separate entities. The masses for which this is possible range from a few hundred million kilograms to about the mass of our Sun.
That leads to a problem, however. Coley and Carr say that since the mass of primordial and pre-crunch black holes is similar, they will be very difficult to tell apart.
Nobody has yet seen a primordial black hole, although efforts are underway to search for the telltale signatures they ought to produce.
Small black holes ought to evaporate away in relatively short period of time, finally disappearing in a violent explosion of gamma rays. The hope is that observatories such as the Fermi Gamma Ray Space Telescope will see such events. Indeed, some cosmologists say this thinking might explain the gamma ray bursts that we already see from time to time.
What all this means, of course, is that there may be objects in our Universe that predate the Big Bang. And if we can somehow find a way to distinguish them from primordial black holes, we may yet be able to observe these most ancient of objects.
Ref: arxiv.org/abs/1104.3796 : Persistence Of Black Holes Through A Cosmological Bounce