Alien worlds orbiting dead stars may be leaving 'electric trails' in space - and astronomers think they know how to find them.

The strange planets are located around pulsars - long-dead stars which form in the aftermath of a supernova.

When a giant star explodes - if it is big enough - it collapses in on itself and forms a neutron star, made of super-dense material. Such a star can be the size of a small city but its mass will still exceed that of our sun.

These stars emit beams of electromagnetic radiation, which can only be seen when it points towards the Earth - meaning it appears to 'pulse' in the sky as it rotates.

But despite the extraordinary density of the star, and the size of explosion which created it, some pulsars have been found with orbiting planets.

Now scientists think they may know how to find more of them.

Fabrice Mottez, an astronomer at the Paris Observatory, thinks they they may interact with the 'winds' of charged particles around a pulsar, and may leave trails of electric current as they move in orbit.

In a new paper, reported by and others, he suggests that radio telescopes be tuned to look for the patter of electric currents around pulsars.

"The detectability of these planets with radio telescopes is currently under study," Mottez told

The four planets found around pulsars so far have relatively similar orbits to Earth, suggesting they were formed after the supernova which exploded the star.

But it is thought that many more planets - probably with elongated, oval orbits - could be found in orbit around pulsars, at much greater distances from the star.

Studies are now commencing on how to look for the trails of electricity, and what they may tell us about the life and death cycles of giant stars in deep space.