This cartoon depicts the Double Pulsar, a pair of stellar corpses bound by gravity (although it is not shown to scale). The corpses spin rapidly, beaming radiation into space. When such a beam sweeps across Earth, we see a brief "pulse" of energy. The Double Pulsar is the only pair of these objects yet discovered. By monitoring changes in their pulses, scientists can learn about the stars themselves and about General Relativity, Albert Einstein's theory of gravity. The system is about 2,400 light-years from Earth. [Michael Kramer (Jodrell Bank Observatory, Univ. Manchester)]
Find out more in our radio program entitled Passing the Test.