Astronomers had already traced a connection between bursts and supernovas. But this burst was so close, and Swift had spotted it so quickly, that scientists hoped it would help confirm what they suspected: A gamma-ray burst is an exploding star's opening act.
After an unusually long flood of gamma rays and x-rays, lasting more than half an hour rather than the typical few seconds, the February 18 burst gave way to visible and infrared light. Within three days this afterglow was fading away—and then the supernova grabbed the spotlight.
Astronomers at the Very Large Telescope in northern Chile were watching the afterglow dwindle when they noticed a brightening. The star had exploded just a minute or so after the burst, but most of its energy was invisible ultraviolet and x-ray radiation. Its visible light had brightened more slowly, and now it was finally outshining the afterglow. For the first time, astronomers had seen a gamma-ray burst evolve into a supernova from the very beginning.
Eighteen days after the supernova flared into view, astronomers were still watching. Atop Palomar Mountain in southern California, the observatory dome's twin shutters slid open under patchy clouds, letting a sliver of night sky fall onto the caged mirror of the 200-inch (500 centimeters) Hale Telescope. Caltech astronomer Avishay Gal-Yam had two hours before the supernova would dip too low in the sky for the telescope to see it.
Still more luminous than a billion suns, the supernova outshone the combined light from all the stars in its home galaxy, glowing white-hot from the radioactive decay of unstable nickel atoms forged in the explosion. Gal-Yam pointed to a computer screen showing a squiggly line—the glow broken down into its component colors, or wavelengths. Each dip in the line represented a wavelength of light absorbed by a different element—silicon, cobalt, calcium, iron—in the debris of the star.
Destruction and creation were conjoined on the screen. The elements revealed there, like those from countless earlier supernovas, will eventually find their way into new stars and perhaps new planets, Gal-Yam said. He added: "I'm just really happy to be observing this."
The star had begun its race to destruction long before that night on Palomar, when it began to lose a lifelong fight against gravity. Gravity is responsible for setting newborn stars aflame, by squeezing atoms of hydrogen in the star's core so tightly that they fuse to make helium. The fusion generates light and heat and also exerts pressure that allows the core to withstand the enormous weight of the star's outer layers.