3C58 is a neutron star a remnant of the supernova explosion seen by Japanese and Chinese astronomers in 1181. Found at RA 02h 05m 37.00s , Dec +64ยบ 49' 48.00" (J2000 coordinates) in the region of the constellation Cassiopea, observations have shown it to be spinning at 15 times a second (making it of the pulsar variety of neutron star) and surrounded by a hot cloud of gas some 20 light-years across.
Work done by Stephen Murray of the Harvard-Smithsonian Center for Astrophysics has revealed some interesting facts about this object, firstly it appears to by spinning at the nearly the same rate as it was when formed (it's only slowing at 10 microseconds a year). This is at odds with the pulsar in the Crab Nebula (which is nearly the same age), which when formed was spinning faster than 3C58, and yet has slowed to half it's initial speed.
Furthermore observations made by the Chandra x-ray telescope have shown that the pulsar emitting 20,000 times less radiation than the Crab pulsar, and the gas surrounding it a 1,000 times less
These observations present the current theory of how such neutron stars form and evolve with a problem; where has all the energy gone: why is it so slow and cold?
One answer could be it is dumping it's energy through an unusually large electromagnetic field, and further out from the star than has been observed will be found traces of the lost energy. Or perhaps the supernova observed in Cassiopea was not due to this star... Actually the lack of any remnants near the reported region of the 1181 event make this unlikely.
Another more interesting explanation recently presented (and due to be published in June this year in the The Astrophysical Journal) is that the star may not be composed of pure neutrons; it may be composed of 'free' quarks that roam through the star. The different compostion, in fact a whole new form of stable matter, could explain the increased energy loss. This would make it a whole new astrophysical object, a quark star and would represent a new object lying in density between a black hole and a neutron star.
For more see :-
http://cfa-www.harvard.edu/newtop/previous/090701.html
http://chandra.harvard.edu/photo/cycle1/0022/