Category: mass gap

New LIGO Events Demolish The Idea Of A ‘Mass Gap’ Between Neutron Stars And Black Holes

“For decades, we knew only of neutron stars that existed below about twice the Sun’s mass, and black holes that existed at or above about five times the Sun’s mass. Beginning in 2017, we started to see neutron stars merging together to form black holes that fell into that empty range, but those events were relatively infrequent. However, this latest discovery — of two low-mass black holes merging together to form a heavier black hole — should close off the “mass gap” range for good.

What was once a region of unknowns should now be filled in by black holes. Although there’s still a lot of science left to do to determine how rare or common black holes of different masses are, particularly in the realm of population statistics, it would now be very surprising if there were a gap in masses between neutron stars and black holes. LIGO’s latest data has demolished that idea. Despite cries of, “NOT NOW LIGO,” the Universe continues to send data our way, and our scientific discoveries go on.”

For decades, we’ve known that supernovae make both neutron stars and black holes. But until LIGO started detecting gravitational waves, we’d never seen a neutron star over 2 solar masses, and we’d never seen a black hole of less than 5 solar masses. Although LIGO saw two neutron stars merge to form a black hole a couple of times, leading to a black hole in that “mass gap” range in both instances, it had never seen two “mass gap” black holes merging before.

Well, we’re almost a year into LIGO’s third (and upgraded) data run, and already it’s seen four, including a new one this past Monday. The mass gap should be gone, and LIGO’s the observatory that demolished it.

Ask Ethan: Did We Just Find The Universe’s Missing Black Holes?

“As interesting as this new black hole is, and it really is most likely a black hole, it cannot tell us whether there’s a mass gap, a mass dip, or a straightforward distribution of masses arising from supernova events. About 50% of all the stars ever discovered exist as part of a multi-star system, with approximately 15% in bound systems containing 3-to-6 stars. Since the multi-star systems we see often have stellar masses similar to one another, there’s nothing ruling out that this newfound black hole didn’t have its origin from a long-ago kilonova event of its own.

So the object itself? It’s almost certainly a black hole, and it very likely has a mass that puts it squarely in a range where at most one other black hole is known to exist. But is the mass gap a real gap, or just a range where our data is deficient? That will take more data, more systems, and more black holes (and neutron stars) of all masses before we can give a meaningful answer.”

Last week, an incredible new story came out: scientists discovered a massive object some 10,000 light-years away that emits no light of its own. From the giant star in orbit around it, we were able to infer its mass to a well-constrained range, with the mean value hovering right at 3.3 solar masses.The lack of X-rays from it, based on the field strength associated with neutron stars and the orbit of the giant star itself, very strongly indicates that this object is not a neutron star, but a black hole.

Does this mean we’ve discovered a black hole in the so-called “mass gap” range? Yes! But does it disprove the existence of a mass gap overall? Not so much. Come get the full story on this edition of Ask Ethan!