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Physicists Are Still Hunting Primordial Black Holes to Solve The Dark Matter Problem

#For a while now, physicists have been hunting for primordial black holes, exotic objects that could have formed in the early #Universe and spawned a whole range of cosmic shenanigans.

#Using a giant 8.2-metre-wide (that’s 27 feet) telescope, physicists from the #University of #California, #Los #Angeles, and the #Kavli #Institute for the #Physics and #Mathematics of the #Universe in #Japan are searching for signs of these objects; discovering them could even suggest our #Universe was breeding baby universes when it was a wee youngster itself.

#What they hope to see won’t exactly be as scandalous as peeping into alternative realities. #But if their new models are correct, and they’re patient enough, they might find a primordial black hole (PBH) floating between us and a nearby galaxy.

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#Discovering such an object has the potential to fill in several gaps in our knowledge on a whole range of phenomena, from the nature of dark matter to the distribution of heavy elements throughout space.

#More tantalisingly, it could also be a clue as to whether our own #Universe is just one of many in a branching family tree of multiverses once spawned as its babies during the cosmic inflation – although plenty of debate would still remain on the latter point.

#Primordial black holes have a lot in common with run-of-the-mill black holes formed by collapsing stars. They are both intense concentrations of matter that pinch surrounding space-time into a singularity, for example.

#Singularities are themselves curious objects, comprising of points where the space-warping physics of general relativity meet the more granular metrics of quantum mechanics. #Unfortunately these two master theories don’t agree on certain crucial details of reality, so nobody is precisely sure what a singularity is.

#Even the surrounding warping of space and time makes a mess of our intuitions, leaving room to speculate that each black hole is an umbilicus to an entirely separate universe.

#It’s not as far-fetched as it sounds. There are plenty of good reasons to think once a tumbling observer crosses the event horizon – a line of no return – space and time become indistinguishable from an expanding universe like ours.

#That would mean that every time a star collapses to form a singularity, our #Universe becomes a parent. #Mazel tov!

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#Where PBHs differ is that they would have been spawned back when our #Universe was maybe around a second old, a time when radiation dominated (and not much else).

#Given enough of a shove in any one area, that concentrated sea of light could tip over the edge into a singularity. #And because conditions were already extreme, the amount of mass required would be far below that needed for even the smallest stellar black holes.

#Primordial black holes are interesting ideas in desperate want of solid evidence. #Unfortunately smaller holes would have long since evaporated in a puff of #Hawking #Radiation. #And anything large enough we’d surely have noticed by now.

#But there are possibilities researchers have yet to rule out.

#In this new model, the team returned to a theory where quantum effects in empty space could create something of a vacuum bubble, providing a seed for collapse.

Their maths shows these conditions during a period of rapid inflation could reasonably create primordial black holes of a range of masses. #Interestingly, some would match what we’d expect of dark matter.

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#It’s an old idea that’s been kicked around for a while, to the extent that it’s looking increasingly unlikely as a candidate. #If a population of these itty-bitty black holes does behave like dark matter, it’ll probably only account for a proportion of it.

#Just to add to the scepticism, the method the team wants to use to search for these objects has also been attempted before.

#Last year, researchers used the #Subaru #Telescope’s #Hyper #Suprime-Cam to collect nearly 200 snapshots of our neighbouring galaxy #Andromeda over the course of seven hours, just to see if a PBH with the mass of our own #Moon might float by.

#Aside from a single ‘maybe’, the experiment didn’t find anything overly exciting.

#But with this new model, the researchers argue if we wait a little longer – like around 88 hours – we just might get lucky this time. #Or at least rule out their prediction.

#Identifying a primordial black hole of this size would provide cosmologists with an object that could help to explain a range of perplexing problems. #Not only might it contribute to our understanding of dark matter, their collisions with neutron stars might explain fast radio bursts.

#We might have already seen a smash-up between these light-weight black holes in a signature of a gravitational wave event that had all the hallmarks of a neutron-star merger, without the flash.

#As to whether these ancient black holes truly house the babies of our own #Universe, we’d need some pretty revolutionary physics to confirm. #But the kinds of black holes produced in this scenario would be just what we’re looking for.

#Fingers crossed #Hyper #Suprime-Cam just might contribute a little something to the family album.

#This research was published in #Physical #Review #Letters.

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