A team of European astronomers has discovered a cosmic time bomb.

"We found a clock that ticks slower and slower, and when it slows down too much, boom! The bomb explodes," team leader Diego Altamirano tells NASA.

Altamirano and several fellow researchers at the University of Amsterdam used NASA's Rossi X-ray Timing Explorer (RXTE) satellite to watch what happens in 4U 1636-53, a binary star system about 20,000 light-years away.

One of the system's two stars is ordinary, but the other is a superdense, superstrong neutron star that is constantly sucking gas off the other star's atmosphere and gathering it on its accretion disk, a spiral of material that orbits it like a skirt.

Several times a day, enough stolen gas builds up on the neutron star's surface that a blinding thermonuclear explosion takes place, quickly spreading to engulf the entire surface.

• Click here to watch a computer animation of the big boom.

Each explosion releases more energy in a matter of seconds than our Sun does in a week — and the neutron star survives intact each time.

Normally, there wouldn't be any way to predict when such an explosion would happen. But RXTE detected a regular pattern of X-ray bursts that seemed to "tick" every 120 seconds, or two minutes.

But after a while, the "ticks" start slowing down. When reach the point where they're every 125 seconds, that's when the colossal explosions take place.

"We can predict when these explosions are happening. We have a clock that tells us when the bomb will explode!" says Altamirano.

• Click here to read more on this story from NASA's Goddard Space Flight Center.