’seeing Double’

Abstract

The initial observation took less than five minutes. A 23 millisecond pulsar 2000 light years away in the constellation of Puppis. Even from the first discovery observation, it was clear that the pulsar was in a short-period binary orbit. Follow up observations revealed signs that the companion was massive, perhaps even a neutron star. Binary pulsars had been discovered before — 80 had been found before this one, and there are now 134 known. The first resulted in Hulse and Taylor receiving the Nobel Prize (see Chapter 9). But while these systems involve a pulsar orbiting with a neutron star, the neutron star companions remained relatively anonymous: even if they are pulsars their beams do not intersect Earth and so remain invisible. Undetectable at the time of this pulsar’s discovery was a much slower, second pulsar signal. If this was indeed a double pulsar, it would provide a unique test bed for the most stringent test ever of Einstein’s theory of gravity, general relativity.