Explosions in Space

Scientists have now identified the types of galaxies where gamma-ray bursts occur - and luckily ours isn't one of them.

Credit: NASA, ESA, Andrew Fruchter (STScI) and the GRB Optical Studies with HST (GOSH) Collaboration A sampling of the host galaxies of long-duration gamma-ray bursts taken by NASA's Hubble Space Telescope.

Gamma-ray bursts don't loiter, and neither can the people who hunt them. That's why astronomer Andy Fruchter has set his cell phone to ring every time one of these massive explosions - packed with the energy of a trillion suns - occurs in outer space. Since the 1960s, when scientists scanning the sky for elicit nuclear tests first witnessed these powerful explosions and misconstrued them for Russian bombs, the origin of gamma-ray bursts (GRBs) has been a mystery. But Fruchter's recent attention to cosmic detail has filled in one of the gaps: he and his team have identified the types of galaxies where these bursts occur in a study published in Nature on May 10.

A GRB, best-described as a flash of very high-energy radiation, can be triggered by the collapse of a massive star. It is always accompanied by a supernova - another type of explosion resulting from the death of a star - and a GRB will be followed by a supernova instants later in a powerful succession of blows. However, although one might expect the two events to form in similar environments, images from the Hubble Telescope collected by Fruchter and other astronomers from the Space Telescope Science Institute in Baltimore show that they don't. In fact, the presence of a supernova doesn't always indicate that a GRB has occurred.

Credit: NASA and A. Feild (STScI) A model of a long-duration GRB.

This is where it gets tricky. Although a GRB is a lot brighter than a supernova, and is observed first, it is actually produced by the supernova, which is typically of much higher energy. Sometimes the collapse of a star will only result in a supernova: for a GRB to occur as well requires the right conditions.