Some black holes are a result of the violent supernovae of massive stars, others have persisted in the cores of the majority of galaxies for billions of years. Some theories suggest (harmless) microscopic black holes might even be spawned by particle accelerators like the Large Hadron Collider.
However, there is another subset of black holes that may have been produced during the initial energetic throes of violence immediately after the Big Bang.
The latter type of ancient black hole - known as "primordial" black holes - may be knocking around during modern times after surviving for over 13.7 billion years, slowly losing mass through the theorized mechanism of Hawking radiation - the only form of radiation thought to escape from the gravitational ferocity of their event horizons.
So, there might be very old black holes, of an assortment of masses, drifting through the Universe, occasionally blipping out of existence, generating a short burst of gamma radiation.
Pre-Big Bang Black Holes?
Primordial black holes have yet to be detected, but in a new paper by Bernard Carr of Queen Mary University of London and Alan Coley from Dalhousie University in Canada, the theory of primordial black holes has been stretched even further. Could there be another type of black hole in our modern universe that was created before the Big Bang?
This new theory is born from the idea that we live in a post-Big Bang universe that was born from another universe that underwent a "Big Crunch." After collapsing through gravitational contraction, all matter in this "pre-Big Bang universe" contracted to a point, bouncing, thus spawning the Big Bang.
But here's the rub, if everything from the previous universe collapsed to a point and then exploded as the Big Bang, wouldn't all information be destroyed? Surely all matter would have been blended together as pure energy and spat back out, producing a universe that bears no resemblance to its progenitor?
Perhaps not, say Carr and Coley; perhaps black holes spawned by the impossibly compact conditions of that dying universe survived the Big Bang and are dispersed throughout the current universe. What's more, the pair of researchers have put size limits on the mass of black holes that might survive the Big Crunch/Big Bang party.
As highlighted by the arXiv blog, pre-Big Bang black holes with masses of a few hundred million kilograms to the mass of the sun might have made it through. Black holes of these masses may have been able to retain their structure, keeping them separate from the Big Crunch singularity that is predicted to form. Then, as the Big Bang exploded to life, these black holes slipped into the new universe... our universe.
This is a pretty heady theory, but it's not the first to suggest some pre-Big Bang artefacts may survive into the modern universe.
In Nov. 2010, British physicist Roger Penrose went on the record to say that it was by his reckoning that there were patterns in the cosmic microwave background radiation (CMBR) - the "echo" of the Big Bang. Penrose's theory is that gravitational waves - "ripples" in spacetime - leaked through from the pre-Big Crunch universe, imprinting the CMBR with detectable rings.
Although Penrose's idea was heavily criticized (cosmologists familiar with the CMBR said that Penrose was seeing shapes and patterns in the random temperature "anisotropies" and not seeing what he thought he was seeing), could Carr and Coley's pre-Big Bang black holes be detected?
Gamma-ray Death Throes
Space observatories such as the Fermi Gamma Ray Space Telescope might detect the death of these black holes. As they evaporate and, on reaching a minimum mass, they are theorized to fizz away, producing a tell-tail gamma ray signal.
Inexplicable gamma-ray bursts are spotted occasionally, but we're a long way from believing they may have a dying black hole source. Also, as the researchers point out, the signals produced by dying pre-Big Bang black holes (if they can indeed be detected) would look identical to the primordial black holes formed after the Big Bang.
There are a lot of if's and but's associated with this work, but it is certainly interesting to discuss the potential of stuff surviving from one universe to the next, therefore speculating on the very nature of our Universe.
Publication: "Persistence of black holes through a cosmological bounce," Carr & Coley, 2011. arXiv:1104.3796v1 [astro-ph.CO]
Source: arXiv blog
Image: Artist impression of a black hole (NASA)