The 4 big black hole frontiers for gravitational waves | by Ethan Siegel | Starts With A Bang! | Feb, 2024
So far, gravitational waves have revealed stellar mass black holes and neutron stars, plus a cosmic background. So much more is coming.
It’s hard to believe, but less than 10 years ago, humanity still wasn’t certain that gravitational waves were real. Sure, we had seen evidence that massive objects in tight orbits were exhibiting orbital decay, but we had yet to directly detect the energy being radiated away from them: theoretically in the form of gravitational waves. All of that changed with the dawn of Advanced LIGO, which detected its first gravitational wave signal — from two merging black holes — on September 14, 2015. In the time since, LIGO has been upgraded, joined by additional gravitational wave detectors, and has seen over 100 mergers and merger candidates, detecting low-mass neutron stars and black holes up to ~100 times the mass of our Sun.
Then, last year, in 2023, a novel method for detecting gravitational waves achieved its first success. By using an array of natural, astronomical clocks — millisecond pulsars — astronomers were able to uncover the first evidence for a low-frequency gravitational wave background to the Universe. The ultimate goal of gravitational wave astronomy is ambitious: a complete census and knowledge of the black hole and neutron star populations that are out there, as well as the event rates for inspirals and mergers throughout cosmic history. Remarkably, there are four frontiers that are actively being pushed back by gravitational wave advances. Here’s what’s coming up to improve our understanding of the Universe.
1.) The most massive black holes of all.
One of the most remarkable aspects of gravitational waves is that they are generated whenever you have:
- one mass,
- in an accelerated motion,
- through a region of curved space,
- caused by the presence of another mass.
