Real events
What’s going on
Pitch rises as the orbit shrinks: closer → faster → higher frequency. That upward sweep is the chirp.
The rate of the sweep is set by the chirp mass — LIGO measures it straight from this sound.
The orbit barely shrinks for most of the time, then collapses in a flash. That is real: the waves carry energy away slowly at first, then faster and faster — and for heavy black holes the whole show is over in a fraction of a second.
The whistle ends abruptly at the last stable orbit: any closer and the two can no longer circle each other — they collide.
After collision the new black hole rings like a struck bell: the ringdown, fading in milliseconds.
The lower plot is a spectrogram of that same sound: frequency vs time. A rising ridge is the chirp. On a real detector trace the ridge sits in noise; the cyan curve is where the math says it should be.
Spin changes the last stable orbit: prograde holes can circle closer, so the whistle climbs higher. Eccentricity makes an oval; they dump energy at the close pass and the oval rounds out. Tides only live on neutron stars — a squashy star rips before the last orbit, cutting the chirp short.
Distance makes the wave quieter (1/D). Redshift stretches time and drops pitch; the 30 Hz wall is in the observed band, so a far-off event only shows its ending.
How to play
- Play. You hear noise, and maybe a rising whistle. Warp only slows the tape; it does not change the score.
- Click the spectrogram (the bottom plot) where the bright ridge ends. That instant is the merger. Hunt score is that click.
- Tune m₁ and m₂. The number that matters is chirp mass (left). Heavier pair → shorter, steeper ridge. Cyan is your guess of pitch vs time; sit it on the ridge. Fit score is that match. Many pairs share one chirp mass — do not hunt each mass alone.
- Spin last. It only bends the end of the ridge. Eccentricity, tides, distance, and redshift are off in Lab.
- Hint says early/late and too heavy/too light without giving the answer. Demo is a loud easy round. Reveal is the answer (honor system).
What the lab is
LIGO does not get a clean whistle. It gets a rising ridge buried in noise. Finding that ridge is the whole game: that is detection.
Then matching chirp mass is a tiny parameter estimate by eye — the same observable LIGO reports first.
Classroom: Copy link. Everyone with that URL gets the same seed, the same noise, the same hidden pair. Hint and Reveal are honor-system; the teacher can just not press them.
WAV downloads this strain (noisy in Lab, clean sim in Instrument) so you can drop it in Audacity or a lecture slide.