For some time now, physicists have been searching for primordial black holes, exotic objects that could have formed in the early universe and generated a whole range of cosmic deceptions.
With a giant telescope 8.2 meters wide (27 feet), physicists at the University of California, Los Angeles, and the Kavli Institute of Physics and Mathematics of the Universe in Japan are looking for signs of these objects; discovering them might even suggest that our Universe was raising child universes when I was a young child.
What they hope to see will not be exactly as outrageous as delving into alternative realities. But if their new models are correct and patient enough, they could find a primordial black hole (PBH) floating between us and a nearby galaxy.
The discovery of this object has the potential to fill various gaps in our knowledge about a whole range of phenomena, from the nature of dark matter to the distribution of heavy elements through space.
More temptingly, it could also be a clue as to whether our own Universe is just one of many in a multiverse branched family tree that appeared as babies during cosmic inflation, although there would still be much debate about this last point.
Primordial black holes have a lot in common with first-generation black holes formed by collapsed stars. Both are intense concentrations of matter that pinch the surrounding space-time into a singularity, for example.
Singularities are curious objects, which include points at which the deforming physics of the space of general relativity meets the most granular metrics of quantum mechanics. Unfortunately, these two master theories do not coincide in certain crucial details of reality, so no one knows exactly what a singularity is.
Even the surrounding deformation of space and time makes a mess of our intuitions, leaving room to speculate that each black hole is a navel of a completely separate universe.
It’s not as far-fetched as it sounds. There are many good reasons to think that once a falling observer crosses the horizon of events (a line without return), space and time become indistinguishable from an expanding universe like ours.
This would mean that every time a star collapses to form a singularity, our Universe becomes a father. Mazel tov!
Where PBHs differ is that they would have been generated when our Universe was perhaps about a second old, a time when radiation dominated (and not much more).
Given enough momentum in any area, that concentrated sea of light could tip over over the edge and turn it into a singularity. And since the conditions were already extreme, the amount of mass needed would be much less than that needed even for the smallest stellar black holes.
Primordial black holes are interesting ideas that desperately need solid proof. Unfortunately, the smaller holes would have evaporated for a long time in a Hawking radiation blow. And anything big enough that we probably would have already noticed.
But there are chances that researchers have not yet ruled out.
In this new model, the team returned to a theory where quantum effects in empty space could create a vacuum bubble, providing a seed for collapse.
His mathematics shows these conditions during a period of rapid inflation that could reasonably create primordial black holes from a range of masses. Interestingly, some would match what we would expect from dark matter.
It’s an old idea that was kicked off for a while, to the point that it seems increasingly unlikely as a candidate. If a population of these funny black holes behaves like dark matter, it will probably only represent a part of it.
Just to add to the skepticism, the method the team wants to use to search for these objects has also been tried before.
Last year, researchers used the Subaru Telescope’s Hyper Suprime-Cam to collect nearly 200 snapshots of our neighboring galaxy Andromeda over the course of seven hours, just to see if there was a PBH with the mass of our Moon.
Aside from a single “maybe,” the experiment found nothing overly exciting.
But with this new model, researchers argue that if we wait a little longer, like about 88 hours, we may be lucky this time. Or at least rule out his prediction.
Identifying a primordial black hole of this size would provide cosmologists with an object that could help explain a number of puzzling problems. Not only could it contribute to our understanding of dark matter, but its collisions with neutron stars could explain gusts.
We could have already seen a shattering between these lightweight black holes at the signing of a gravitational wave event that had all the characteristics of a neutron star fusion, without the flash.
To know if these ancient black holes really house babies in our own universe, we would need a pretty revolutionary physics to confirm that. But the type of black holes produced in this scenario would be just what we are looking for.
The fingers that crossed Hyper Suprime-Cam could only contribute something to the family album.
This research was published in Physical review letters.