This picture shows a nebulous 'knot' next to the pulsar in the Crab Nebula. The pulsar is the brighter object of the close pair at the center of this image. The dimmer object next to the pulsar is the 'knot' of nebulosity. It is actually about 5 billion kilometers (140 billion miles, or 1,500 times the distance from the Earth to the Sun) from the pulsar. The two objects appear to be close to one other because they are being viewed at the distance of the Crab Nebula, about 6,000 light years from the Earth.
The knot may have been present for a long time, or it may be a new phenomenon. Previous telescopic observations were incapable of distinguishing it. According to one theory, the knot may be the location where a high-speed wind of electrons and positrons streaming outward from the pulsar undergoes a shock wave, resulting in material piling up like snow on the blade of a plow. The line from the pulsar to the knot lies along the direction of a jet structure of uncertain nature that can be seen in x-ray images of this region. This jet may extend from the polar cap of the pulsar.
The wispy structures seen in this image are not shreds of the exploded supernova star, but a less well-understood phenomenon that appears to be directly associated with the pulsar. Time sequences of photographs made in past years with telescopes on the ground, while much less sharp than this HST image, indicate that these pulsar wisps move, or that they appear and disappear, or both.
Camera: WFPC2
Credit: J. Hester and P. Scowen (Arizona
State University), and NASA
