This simulation shows the radiation emitted from a binary black hole system. In principle, we should have neutron star binaries, black hole binaries, and neutron star-black hole systems, covering the entire allowable mass range. In practice, we saw a longstanding ‘gap’ in such binaries between about 2.5 and 5 solar masses. With the newest LIGO data, that gap seems to disappear. (Credit: NASA’s Goddard Space Flight Center)

New black hole discovery proves it: ding, dong, the “mass gap” is dead

The latest gravitational wave data from LIGO and Virgo finally shows us the truth: there are no “gaps” in the masses of black holes.

How massive can the most massive neutron star be, and how light can the lightest black hole be? For the entire history of astronomy up until 2015, our understanding of both of these phenomena was limited. While both neutron stars and black holes were thought to have formed by the same mechanism — the core-collapse of a massive star’s central region during a supernova event — observations only revealed low-mass neutron stars and black holes whose masses were significantly higher. While neutron stars seemed to top out at around twice the mass of the Sun, the least massive black holes didn’t appear until we got up to around five solar masses. This in-between region, puzzlingly, was known as the “mass gap.”

Starting in 2015 with the twin LIGO detectors, however, a fundamentally new type of astronomy was born: gravitational wave astronomy. By detecting the ripples in spacetime that emerged from the inspiral and merger of these very objects — black holes and neutron stars — we could infer the nature and masses of both the pre-merger and post-merger objects that resulted. Even after the…