Craig B. Markwardt

A gamma-ray burst is a short but incredibly powerful explosion in a distant galaxy. In a few seconds, it releases as much energy as the Sun will emit over billions of years. The Neil Gehrels Swift satellite catches such flashes with a special telescope called BAT, which detects gamma rays.

The lighthouse in the Crab Nebula blinks thirty times per second. It's a pulsar — a dead star that, as it spins, shoots out narrow beams of light, and Earth sweeps through them like a ship crossing a lighthouse beam. This lighthouse has two beams: the main pulse and the interpulse.