NASA satellite pins down timer in stellar ticking time bomb

This image illustrates a thermonuclear explosion as it ignites, and beings to spread. It will engulf an entire neutron star. Click here for more information.

GREENBELT, Md. - Using observations from NASA’s Rossi X-ray Timing Explorer (RXTE), an international team of astronomers has discovered a timing mechanism that allows them to predict exactly when a superdense star will unleash incredibly powerful explosions.

"We found a clock that ticks slower and slower, and when it slows down too much, boom! The bomb explodes," says lead author Diego Altamirano of the University of Amsterdam in the Netherlands.

The bursts occur on a neutron star, which is the collapsed remnant of a massive star that exploded in a supernova. The neutron star belongs to a binary system that can be described as a ticking time bomb. Hydrogen and helium gas from a companion star spirals onto the neutron star, slowly accumulating on its surface until it heats up to a critical temperature. Suddenly, the hydrogen and helium begin to fuse uncontrollably into heavier elements, igniting a thermonuclear flame that quickly spreads around the entire star. The resulting explosion appears as a bright flash of X-rays.

These bursts, which can occur several times per day from the same neutron star, release more energy in just 10 to 100 seconds than our Sun radiates in an entire week. Put another way, the energy is equivalent to 100 fifteen-megaton hydrogen bombs exploding simultaneously over each postage-stamp-size patch of the neutron star’s surface.

Scientists have observed thousands of these X-ray bursts from about 80 different neutron stars. But until now, they had no way to predict when they would occur.