A Gravitational Wave Surprise

submited by

Style Pass

2024-10-16 15:30:14

I think gravitational wave astronomy is one of the most exciting breakthroughs we’re tracking on Centauri Dreams. The detection of black hole and neutron star mergers has been a reminder of the tough elasticity of spacetime itself, its interplay with massive objects that are accelerating. Ripples in the fabric of spacetime move outward from events of stupendous energy, which could include neutron star mergers with black holes or other neutron stars. Earth-based observing projects like LIGO (Laser Interferometer Gravitational-Wave Observatory), the European Virgo and KAGRA (Kamioka Gravitational Wave Detector) in Japan continue to track such mergers.

But there is another aspect of gravitational wave work that I’m only now becoming familiar with. It’s background noise. Just as ham radio operators deal with QRN, which is the natural hum and crackle of thunderstorms and solar events, so the gravitational wave astronomer has to filter out what is being called the astrophysical gravitational wave background, or AGWB, as the inevitable acronym would have it. Astronomers also have to consider GW signals associated with events in the early universe, stochastic background ‘static’ that could have originated, for example, in cosmic inflation or the creation of cosmic strings.

The AGWB is the background noise of countless astrophysical events, a ‘hum’ from all sources emitting gravitational waves in the universe. Recent work has been showing that this collective signal, primarily from black hole and binary neutron star mergers, is detectable by the technologies we’ll be deploying in the 2030s in the European Space Agency’s Laser Interferometer Space Antenna (LISA) mission. And it’s clear that for gravitational wave astronomy to proceed, we need to remove the AGWB to uncover underlying signals.