ABSTRACT
Normally, the pulses from a rotating neutron star can be timed with great precision. The period of PSR 1829-10 was 330 milliseconds, but Setnam Shemar, a graduate student working at Jodrell Bank with Andrew Lyne's team, found that it was not constant; sometimes the pulses arrived earlier than predicted, while at other times they were late. Shemar found that they were cyclic, and he decided that the cause of this strange phenomenon was movement. The neutron star was moving round the common centre of gravity of a binary system, and though the companion body could not be seen it was making its presence felt. When the neutron star was moving toward us (due aLlowance having been made for the overall motion in space) the pulses were early; six months later they were behind schedule, because the neutron star was then in the far pan of its orbit and the pulses had further to travel. Everything pointed to the existence of a neutron star with 1.4 times the mass of the Sun, together with a planet 10 times as massive as the Earth, moving round
