Further, the pulsar's motions toward or away from Earth--not analyzed in the study--would change calculations of its velocity and thus its age, Cordes says.
By tracking the system's evolution, Ransom and colleagues should be able to tell whether either the inner white dwarf or the pulsar falls faster toward the outer white dwarf and test strong equivalence about 100 times as precisely as before, Damour says.
When the companion runs out of nuclear fuel and puffs up as a bloated old star, intense gravity can pull its outermost gas toward the pulsar.
They concluded from these signals that the pulsar must be alternately moving toward and away from the Earth i.e., that it must be orbiting around a companion star, which the two men deduced was also a neutron star.
That's because Earth's motion in its orbit, either toward or away from the pulsar, stretches out or bunches up the wavelength of the radio signal, in an effect much like a Doppler shift.
The idea is analogous to what happens with a regular x-ray pulsar: Gas from a normal star is pulled toward an orbiting neutron star, where it first piles up in a spinning disk and then spirals down onto the neutron star's surface.
The small star and its planet probably formed in the suburbs of the star cluster, then migrated toward the center and came too close to the ancient pulsar, which captured them.
They could not be survivors of the supernova explosion that formed the pulsar, but they may have formed from a disk of stellar material that fell back toward the pulsar after the supernova.
This constellation also contains the isolated pulsar Geminga.
Dr. David J. Helfand, a Columbia University specialist in pulsar research, said that until now, scientists knew of one reliably dated pulsar, the one in the Crab Nebula.
