Dead Stars Captured by a Dying Hubble

On some nights, Astronomer Andrew Fruchter is jolted from sleep by a Prokofiev theme blaring from his cell phone. The urgent message: a massive star died at the edge of the universe—several billion years ago. Unable to fight the force of gravity, the star collapsed into a black hole, setting off a huge supernova explosion, and releasing a jet of high-energy light. And now, after traveling billions of light-years, the jet’s extraordinary blaze has been spotted by satellite telescopes. The star’s collapse was long over, but the astronomer’s work had just begun.

For four years, Fruchter and his colleagues at the Space Telescope Science Institute in Baltimore, MD, have worked to pinpoint the source of these stellar explosions, called long gamma ray bursts, or LGRBs. Packing enough energy to supply the world’s electric needs for a billion billion billion years, a LGRB in our galaxy could obliterate the planet. But Fruchter’s most recent research, soon to be published in Nature, radiates good news: LGRBs don’t occur in our kind of galaxy. Based on photographs taken by the aging Hubble telescope, his work might also give reason for its contested, expensive repair.

With photos taken by the Hubble Space Telescope between February 1997 and October 2004, Fruchter compared the luminescence of galaxies containing LGRBs to those with core collapse supernovae, the celestial phenomena that spawn LGRBs. Core collapse supernovae are gigantic explosions that occur throughout the universe when a massive star runs out of nuclear fuel. But Fruchter’s photos indicate that the select few supernovae that produce LGRBs go off in specific types of galaxies—those that are small, non-spiral, and have clumps of very bright stars rather than an even distribution. They’re “scruffy little things,” Fruchter says, “not your normal, pretty galaxies.” In other words, they’re not like ours.

But why do LGRBs occur in these particular galaxies? Fruchter says LGRB galaxies are not very chemically evolved. That is, they’re made up of mostly hydrogen gas, while other galaxies—like ours—contain life-giving elements like carbon, oxygen, and nitrogen. Fruchter speculates that in evolved galaxies, these ions interact with the stream of protons and electrons that normally encircle a star, causing the star to lose a lot of mass. What’s more, he thinks the ions create a magnetic field that keeps the star from spinning as fast as it would in a galaxy made of only hydrogen. With less mass and slower spins, this means the stars in our galaxy are less likely to form the black holes that lead to LGRBs.

Astronomers detect a LGRB using the three telescopes of the “SWIFT” deep-space satellite. First, one of the telescopes detects the gamma rays of the LGRB. Within seconds, the other two “swiftly” look for the x-rays and visible light rays of the afterglow, to determine the LGRB’s exact position. The data relays to ground computers, which then pass it on to Fruchter’s cell phone. Prokofiev blares, and as Fruchter explains, “then I have to get ground-based telescopes to go follow these things.” And finally, the Hubble can take a picture. In recent months, NASA has been debating whether to give the 15-year-old telescope and its aging parts a $700 million tune-up. Fruchter is optimistic, speculating, “If they can get the shuttle working again, I think they’ll service Hubble.” If the Hubble is put to bed, Fruchter’s research will be too. But at least he’d get a good night’s sleep.