Scientists have found signs of a new kind of gravitational wave. It's really big

https://www.npr.org/2023/06/28/ [login to see] /new-gravitational-wave-supermassive-black-hole
Scientists say they are starting to find signs of an elusive type of rumbling through space that could be created by the biggest, baddest black holes in the universe.

The discovery means that astrophysicists may have opened a whole new window onto supermassive black holes. These mysterious, extremely dense objects, millions to billions of times more massive than the sun, sit at the center of galaxies like our own.

When two galaxies merge, the enormous black holes at their centers are thought to come together and circle each other in a spinning dance that sends giant waves spiraling out.

These waves are like the ripples that move through a pond if you toss in a rock — only these waves move through the very fabric of the universe, and researchers have been eager to study them.