Pin It

Almost a decade ago, Feryal Özel and her colleagues noticed something odd. While a variety of possible black holes had been found in our galaxy, none appeared to fall below a certain size. “There seemed to be a dearth of black holes below 5 solar masses,” she said. “Statistically, this was very significant.”

Since Özel, an astrophysicist at the University of Arizona, published a paper on the problem in 2010, this so-called mass gap has gone unexplained. Even after the LIGO and Virgo gravitational wave detectors started to identify dozens of hidden black holes — including a few surprises — the mass gap appeared to hold firm.

In time, astrophysicists such as Özel began to wonder: Are small black holes just hard to find, or might they not exist at all? “It’s important to establish observationally whether this gap is real, or whether it’s an observational artifact,” said Vicky Kalogera, an astrophysicist at Northwestern University and a leading member of the LIGO team.

To read more, click here.