In 2015, after a century of speculation, the world finally detected the elusive ripples in the universe’s fabric known as gravitational waves. This happened when a wave-hunting experiment called LIGO, which acts like a colossal tuning fork, sensed these waves hurled out from the cataclysmic collision of two massive black holes. (Read more: What is LIGO?)
But where are these collisions occurring? A new paper about LIGO’s third gravitational-wave detection, announced June 1, suggests that the black hole smashup might well have been inside of a beautiful object called a globular cluster—a glittering celestial “snow globe” filled with hundreds of thousands of closely-packed stars. At their centers, globular clusters are believed to harbor dozens to hundreds of black holes—by far the greatest concentration of these exotic objects found anywhere in the universe.
Globular clusters could very well be a major source of the gravitational waves scientists are sensing with LIGO. Studying these waves could teach us more about their dense, star cluster origins, and in the process also shed light on the construction of galaxies, the universe’s biggest groupings of stars.
The Kavli Foundation spoke with three astrophysicists about the many scientific opportunities globular clusters present for understanding the collisions of black holes as well as the workings of the broader cosmos.
The participants were: