What the heck is the LIGO chirp?

I recently posted a track on SoundCloud that included the sonification of LIGO’s gravitational wave data. A student asked me what that meant. Since today is Albert Einstein’s birthday, what better time to try to formulate an answer? https://soundcloud.com/ethanhein/ligo-chirp First, some context: 1.3 billion years ago, two black holes collided. Each was about thirty times as …