Pulsars. They're the skeletons of stars gone wrong. With every object, there is a death. A decaying point at which it stops or begins to stop existing or living. That includes stars. A star's death is not a sad funeral where a handful of people wearing black go to mourn, but rather an explosion. The term for such an explosion is supernova. When a star collapses, it exhausts all of it's energy into a massive combustion, which is known as the most violent, powerful event in the universe. What is left behind is a small ball of light, not very large, yet extremely heavy. A pulsar. Basically, it's a rotating neutron star, or highly compacted core of a dead, massive star. It emits radioactive pulses at a high frequency while rotating, hence the name. They send out a pulse every time a clock ticks to show a second has passed. Such a high fire rate.
Not to be confused with quasars, which basically emit huge amounts of energy and sometimes cause black holes at the center of younger galaxies. For more information, go to the site below.
http://www.seasky.org/celestial-objects/pulsars.html
"A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying.