| The Crab Nebula is the best-studied individual object on the sky. About 40 papers are published about it every year, since more than 40 years. Yet, this supernova remnant is far from being well understood. It contains 100 times less kinetic energy than what is normally released by core-collapse supernovae, which makes it by far the weakest SN explosion of this type known. In addition, scientists believe that the Crab Nebula should contain several solar masses more than what is actually observed. This puzzle has been around for more than 2 decades, and only recent years have seen observational progress in the field.
The solution comes in form of a hypothetical fast-moving and hydrogen-rich shell around the Crab Nebula, which would carry most of the missing kinetic energy and mass. This shell turns out to be of exceedingly low surface brightness, which is why it defied direct detection until very recently when we detected it in deep H-alpha images (Tziamtzis et al., 2007).
The fact that the recorded surface brightness of an extended astronomical object depends only on the f-ratio of the telescope used, but not on its total aperture, makes a detection of the Crab halo feasible with amateur telescopes. We have started the present observational campaign, asking amateur astronomers with suitable equipment and dark locations to obtain as much images as possible. We target for 100+ hours of exposure time in H-alpha filters. The combined ultra-deep image will help us to find an answer to the mystery of the Crab Nebula and the related supernova explosion.
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