2.3.9 Black holes
A black hole may form when a massive star runs out of fuel causing it to collapse.
As the collapse continues, the core will become so dense that nothing, not even light, can escape the gravitational pull of the core. At this point, a black hole will have formed. Alternatively, if a single star is massive enough, the supernova explosion that forms the neutron star might not be able to release sufficient energy to eject all the outer layers of the star. That material will then fall back onto the newly-born neutron star, causing it to collapse to form a black hole.
Astronomers have found that black holes can have very strong magnetic fields which might be related to bright jets of radio signals from the black holes.