You know it if you have been working for one: start-ups are a bit like Quasars. They burn incredibly much material (= money) for a limited period of time, in the center the pressure is immense, and they emit an overwhelming amount of matter, too, although they are very small. Most of them end as a big black hole where everything vanishes (all material or the money of the investors). When the supply is exhausted, the quasars burn out but the black holes remain. Everything is gone. Some quasars are responsible for the formation of galaxies (= companies). Actually, they are supposed to form the core of very young galaxies. If you want to know how a quasar looks like, the artist Don Dixon has created a nice painting of a quasar, see here.
(The image of a quasar or growing black hole is from Wikipeda and can be found here)