The universe has a low-frequency hum, and we finally heard it
For decades, physicists theorized a persistent echo of gravitational waves permeating the cosmos. Now, using a galaxy-sized antenna of cosmic clocks, astronomers have detected the first compelling evidence of this elusive, low-pitch hum vibrating through the Milky Way.
The discovery, announced in late June 2023, provides direct evidence of a gravitational wave background—a field of low-frequency energy flowing through space. While the LIGO network has previously detected high-frequency waves from smaller black holes, this new signal exists at a much lower frequency. This background is thought to be a persistent echo from events occurring shortly after the Big Bang or from the slow, cosmic dances of supermassive black holes.
To capture these subtle ripples, researchers utilized a pulsar timing array, specifically through the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). This method treats millisecond pulsars—dead, rapidly rotating neutron stars that spin up to 700 times per second—as ultra-accurate cosmic clocks. As gravitational waves pass through our galaxy, they physically alter the distance between Earth and these pulsars, causing their radio pulses to arrive slightly early or late.
The detected signal is consistent with the expected energy from pairs of supermassive black holes, some weighing billions of suns, as they orbit each and shrink their paths over millions of years. While the exact cause of the hum is not yet definitively known, the findings confirm standard models of galaxy formation and black hole growth. This breakthrough suggests that hundreds of thousands or even millions of such massive mergers may occur in the next few hundred thousand years, offering a new window into the evolution of our universe.
Source: Was the Gravitational Wave Background Finally Discovered?!?
