Neutron Star

With twice the mass of the Sun crammed into a space no larger than a small city, a neutron star is fantastically dense. A sugar-cube-sized piece of neutron star would weigh billions of tons.

Neutron stars rotate rapidly. This is because the original stellar core was rotating, and as it collapsed its rotation rate increased, in the same way figure skaters spin increasingly rapidly by drawing their extended arms in to their sides.

Neutron stars also have intense gravitational and magnetic fields. The gravity is strong because there is so much matter packed into so small a radius. If a friend dropped you onto a neutron star from, say, 50 million miles out, you would impact and explode with a blast larger than that of any current nuclear warhead. The magnetic field is strong because it is an intrinsic property of the neutron star's matter. When the original stellar core collapses, its magnetic field collapses with it and intensifies until it is a trillion times as strong as Earth's.