Physics, Plainly.

Audio Explainer

The Day We Heard Two Black Holes Collide

In 2015, two LIGO detectors recorded a tiny distortion in spacetime from two black holes merging more than a billion years away.

This story explains what the famous gravitational-wave “chirp” really was, how four-kilometer laser interferometers measured an almost impossibly small change in distance, and how scientists established that the signal was real.

Audio Explainer

Gravitational Waves & Black Holes

What you'll hear

Follow the story of GW150914, the first direct detection of gravitational waves. You’ll hear why the signal reached the Livingston and Hanford detectors about seven milliseconds apart, why a gravitational wave is not an ordinary sound wave, how LIGO compares laser light across four-kilometer arms, what the rising “chirp” reveals about two merging black holes, and how researchers ruled out local noise and instrument problems before announcing the discovery.

Chapters

  1. A Signal Before the Run Had Even Begun
  2. Einstein’s Ripple
  3. Comparing Two Paths of Light
  4. Four Kilometers on a Noisy Planet
  5. The Chirp
  6. Two Black Holes We Could Not See
  7. How Do We Know It Was Real?
  8. A New Sense for Astronomy

About this audio

This is a standalone Physics, Plainly. story audio. It is not a word-for-word reading of an existing article.

It follows the discovery of GW150914 from the gravitational-wave prediction and the engineering of LIGO to the signal itself, the black-hole merger inferred from its waveform, and the evidence used to establish that the detection was real.

The script was researched from primary LIGO materials and other authoritative scientific sources, then rewritten specifically for listening.

Sources

  1. Observation of Gravitational Waves from a Binary Black Hole Merger — LIGO Scientific Collaboration and Virgo Collaboration
  2. Observation of Gravitational Waves from a Binary Black Hole Merger — Science Summary — LIGO Scientific Collaboration
  3. GW150914: The Advanced LIGO Detectors in the Era of First Discoveries — LIGO Scientific Collaboration
  4. How Do We Know GW150914 Was Real? — LIGO Scientific Collaboration
  5. The Newest Search for Gravitational Waves Has Begun — LIGO Lab / Caltech
  6. Audio Files — Gravitational Wave Open Science Center