Such 'planets in the dark' have turned out to be incredibly rare, and astronomers are puzzled over where they come from. The supernova explosion should destroy any pre-existing planets, and so the neutron star needs to capture more raw materials to form its new companions. These after-death planets can be detected because their gravitational pull alters the times of arrival of radio pulses from the neutron star, or 'pulsar', that otherwise pass us by extremely regularly.
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The new work appears in: "The Geminga pulsar wind nebula in the mid-infrared and submillimetre", J. S. Greaves and W. S. Holland, Monthly Notices of the Royal Astronomical Society Letters, in press. A preprint of the paper is available here.
Cardiff University School of Physics and Astronomy