Long-time Slashdot reader fahrbot-bot quotes Quanta magazine: It was an old idea of Stephen Hawking’s: Unseen “primordial” black holes might be the hidden dark matter. It fell out of favor for decades, but a new series of studies has shown how the theory can work… Their very blackness makes it hard to estimate how many black holes inhabit the cosmos and how big they are. So it was a genuine surprise when the first gravitational waves thrummed through detectors at the Laser Interferometer Gravitational-Wave Observatory (LIGO) in September 2015. Previously, the largest star-size black holes had topped out at around 20 times the mass of the sun. These new ones were about 30 solar masses each — not inconceivable, but odd. Moreover, once LIGO turned on and immediately started hearing these sorts of objects merge with each other, astrophysicists realized that there must be more black holes lurking out there than they had thought. Maybe a lot more. The discovery of these strange specimens breathed new life into an old idea — one that had, in recent years, been relegated to the fringe. We know that dying stars can make black holes. But perhaps black holes were also born during the Big Bang itself. A hidden population of such “primordial” black holes could conceivably constitute dark matter, a hidden thumb on the cosmic scale… Following a flurry of recent papers, the primordial black hole idea appears to have come back to life. In one of the latest, published last week in the Journal of Cosmology and Astroparticle Physics, Karsten Jedamzik, a cosmologist at the University of Montpellier, showed how a large population of primordial black holes could result in collisions that perfectly match what LIGO observes. “If his results are correct — and it seems to be a careful calculation he’s done — that would put the last nail in the coffin of our own calculation,” said Ali-Haïmoud, who has continued to play with the primordial black hole idea in subsequent papers too. “It would mean that in fact they could be all the dark matter.” “It’s exciting,” said Christian Byrnes, a cosmologist at the University of Sussex who helped inspire some of Jedamzik’s arguments. “He’s gone further than anyone has gone before….” And with every subsequent observing run, LIGO has increased its sensitivity, allowing it to eventually either find such small black holes or set strict limits on how many can exist. “This is not one of these stories like string theory, where in a decade or three decades we might still be discussing if it’s correct,” Byrnes said. Read more of this story at Slashdot.