Image: Pulsar diagram
NASA / JPL
As pulsars A and B orbit each other, their positions at times cause A to illuminate the lighthouse-like beam of B, increasing the brightness of the B beam.
By Senior Science Writer
updated 5/4/2004 9:51:07 PM ET 2004-05-05T01:51:07

In a stellar version of the walking dead, one near-corpse of a star jump-starts the heartbeat of its close companion as the two spiral toward an eventual embrace that will destroy them both.

The intriguing setup involves two neutron stars, the collapsed remains of regular stars which are now so dense a teaspoonful would weigh billion tons or so on Earth. The stars are so massive that they curve space and time in ways astronomer think they can predict.

One of the stars spins on its axis hundreds of times every second, the other rotates once every 2.8 seconds. They dance around one another every 2.4 hours, travelling at a remarkably swift 0.1 percent of the speed of light.

A catastrophic fate awaits the pair. Meanwhile, researchers have been examining a strange heartbeat emanating from the scene.

Unique system
The stars were discovered last year. Scientists said then that one was a pulsar, so named because its intense magnetic field sends a beam of radio energy into space, and the beam sweeps across the sky, aiming at Earth once each revolution to create a pulsating effect from our vantage point. Further investigation showed that the other star is a pulsar, too. It is the only known double-pulsar system.

The new study, reported in last week's issue of the journal Nature, finds that the pulses of one of these cosmic lighthouses periodically jump-start the pulses of the other, when they are aligned a certain way.

The beam from one of the stars, referred to as pulsar B, is particularly strong at two certain spots in its orbit. "It's as though something is turning B on and off," said Fredrick Jenet of NASA's Jet Propulsion Laboratory, who along with Scott Ransom of McGill University developed a theoretical model for what's going on.

The researchers say the B beam gets bright only when the region from which it emanates gets illuminated by the beam from pulsar A.

Both objects emit tremendous amounts of particles, which are related to the production of the beams. In essence, the emission from B is somehow stimulated when the beam of A sweeps through the emission region of B, the researchers theorize.

We'll soon know
Importantly, the explanation also describes how the stars are configured in relation to one another, and it can be proved out. Along with the explanation comes a prediction: The alignment of each star's axis and the curvature of space-time due to the massive stars causes pulsar A to wobble on its axis, over many years, like a child's top that is slowing down.

In either 4.5 or 14 years — depending on which of two models is right — the much brighter A pulsar will essentially disappear from our point of view.

Here's why: The radio beams emanate in a cone from the magnetic poles of the stars, Ransom explained. As the axis of pulsar A wobbles, it will eventually tilt the beam away from us. At 2,000 light-years away, the otherwise relatively dark star won't offer any other visible evidence to Earth-bound telescopes.

It's not known yet if the weaker beam of pulsar B will still sweep across our line of sight.

"Nature has provided a magnificent spectacle," says Duncan Lorimer of the University of Manchester in the United Kingdom. Lorimer wrote an analysis of the study for the journal. "Time, however, is most definitely of the essence as these two neutron stars may not be visible for much longer."

And eventually, something even more interesting will happen.

In the initial study of the two-star system, named J0737-3039, scientists concluded that their dynamic interaction is warping the fabric of space-time in a fateful manner.

The objects will one day merge in a powerful collision that will mess with space-time dramatically and spawn, in theory, gravitational waves. Observatories designed to detect such events could be successful by the end of this decade.

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