Simeis 147 is a large mature supernova remnant in the constellation Taurus. Although long thought to be almost 100,000 years old, more recent data indicate a younger estimate of about 30,000 years. As most supernova remnants are well dispersed by 100,000 years, the younger estimate is likely to be accurate. S147 spans about 100 light years (about 3 degrees or 6 full moons) and is expanding at about 1000 kilometers per second.
The aftermath of a supernova often leaves a spinning neutron star or pulsar behind, formed from the collapsing core of the dying star. The S147 pulsar has recently been detected and is known as PSR J0538+2817. As is typical of pulsars it is currently spinning at about 7 times per second.