But when the core consumes all of its hydrogen, gravity compresses it. The temperature of the shrinking core rises to about a hundred million degrees, hot enough for helium nuclei to fuse and make carbon. The new surge of energy keeps the core from collapsing much further.

For an isolated star no heavier than the sun, there is little more to the story. The star burns all of its helium and shrivels. It turns into a white dwarf about the size of Earth, aging and cooling indefinitely—unless it lies close enough to another star to steal its neighbor's outer layers of hydrogen. If enough material falls onto the white dwarf, the siphoned fuel ignites a thermonuclear explosion. As the detonation spreads, the entire star blows up in what is known as a type 1a supernova—a giant nuclear bomb.

The supernova blossoming over Palomar was a different kind: not a thermonuclear blast but a star's catastrophic collapse. This is the only kind of supernova that can unleash a gamma-ray burst, and it is the inevitable fate of a star more than eight times as massive as the sun.

Such heavyweight stars always lose their battle with gravity. With the crushing weight of the star's outer layers bearing down on its core, the fusion reactions don't stop at carbon. The star continues to cook lighter nuclei into progressively heavier elements, but each nuclear reaction runs its course faster. The transformation from carbon to oxygen takes 600 years, from oxygen to silicon 6 months, from silicon to iron a day. Once the star's core turns to solid iron—a sphere no bigger than Earth that weighs as much as the sun—its fate is sealed. In less than a second, the star will explode.

Iron marks the end of the road because unlike lighter elements, iron atoms consume rather than create energy when they fuse. Fusion can no longer provide the energy to support the star's outer layers, and the core simply implodes. Usually the result is a neutron star, a stellar cinder so dense a teaspoon would weigh more than a billion tons. In the most massive stars the collapse leaves only a voracious pit called a black hole.

At this point, Woosley believes—before the collapse somehow turns into an explosion—some supernovas unleash a blast of gamma rays. Woosley's interest in these bursts goes back decades, when they were so mysterious that over a hundred more or less serious ideas about their cause were in play, from "starquakes" to the exhaust plumes of alien spacecraft. But his fascination deepened in the early 1990s, when a spacecraft called the Compton Gamma-Ray Observatory showed that gamma-ray bursts originate far beyond our galaxy. To appear as bright as they do, they had to be more energetic than anyone had imagined—far brighter than supernovas, Woosley's first love.