Portal:Astronomy/Picture/Week 23 2006
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Near the centre of the globular cluster M4 lies the pulsar PSR B1620−26. The pulsar is extremely dense and only a few miles across, and rotates about 100 times per second, directing a pulse of electromagnetic radiation towards the earth once during each rotation. Small variations in the intervals between pulses reveal the presence of both a white dwarf and a large Jupiter-sized planet orbiting the pulsar.