Why is it thought that quasars probably spend only a fairly short time in their highlyluminous phase?
A)because there aren't many quasars around today
B)because there aren't any quasars closer than about a redshift of 1
C)because all quasars are at about the same epoch, narrowly defined in time
D)because a black hole could not power a highly luminous quasar for more than a few millionyears
E)because quasars are known to be the consumers of massive galaxies

Question

Quizplus · Accepted Answer

It is believed that the energy source of quasars is a supermassive black hole at the center of a galaxy. It is thought that the black hole consumes nearby gas and dust and becomes highly luminous, producing a quasar. However, this process is not sustainable for more than a few million years, after which the supply of nearby gas and dust is depleted. Therefore, it is thought that quasars probably spend only a short time in their highly luminous phase. The luminosity of a quasar is believed to be powered by accretion onto a supermassive black hole. However, the fuel supply for this accretion is finite, and eventually, the black hole will consume all available matter and the luminosity will decrease. Therefore, it is thought that quasars likely spend only a fairly short time in their highly luminous phase, possibly lasting only a few million years.

Why Is It Thought That Quasars Probably Spend Only a Fairly