Linked from
The 15 pages that link to Crab Nebula, each with the reason it gives.
Messier catalogBroader topic: M1 is the catalog’s first entry and a remnant of an exploded star.
NebulaBroader topic: It is a well-studied nebula powered by a pulsar left after a supernova.
Messier objectBroader topic: It is the first object in Messier’s catalogue.
Argon compoundsBroader topic: Astronomers detected argon hydride ions in its hydrogen-rich regions.
SN 1054Broader topic: It is the expanding debris left by SN 1054.