Light fades like a campfire when you stop adding wood. Gamma-ray bursts, the brightest explosions in the Universe, have their own rhythm of fading. Astronomers took 85 such bursts caught by the Swift satellite and looked at how fast their brightness drops.
Inside a burst hides a black hole that greedily sucks in matter. It shoots out two narrow jets, and it's these jets that shine. But what spins up those jets? There are two suspects. The first: magnetic fields twisted around the hole like a spring. The second: neutrinos, ghostly particles born in the scorching disk around the hole, which carry away energy. Each mechanism leaves its own signature: magnetic fields quench the light slowly, neutrinos — quickly.
The scientists compared the slopes of 85 bursts with predictions. 15 bursts fell on the magnetic-field line, 22 on the neutrino line. But most landed in between. So nature doesn't pick just one: both mechanisms work together, though neutrinos more often hog the blanket.
Now astronomers have a simple tool: measure the slope, and you know what's inside. The light fades, and we read its dying like a book.
In a few seconds, a gamma-ray burst can release as much energy as the Sun will emit over its entire lifetime — about 10 billion years.
In Dan Simmons' novel 'Hyperion', gamma-ray bursts are weapons that destroy entire planets.