What is believed to be the status of quasars in the present universe?
A)A quasar is an evolutionary stage between spiral galaxies and giant ellipticals, and the evolutionary transformation is ongoing.
B)There are no quasars closer than about 800 million ly. Since their lifetimes are shorter than this, all have burned themselves out and are extinct.
C)Quasars appear only in very young galaxies. As a result, we find new quasars only in the centers of rich clusters where new galaxies are being formed.
D)Quasars date from an early time in the history of the universe when galaxies were more plentiful and collisions were more frequent-like the planetesimals in the early solar system. Quasars result from collisions of protogalaxies. This era of collisions has past and there are no more quasars.

Question

Quizplus · Accepted Answer

Quasars are extremely luminous active galactic nuclei, powered by supermassive black holes accreting matter. They are observed at great distances, implying that they are phenomena from the early universe. The fact that there are no quasars closer than about 800 million light-years suggests that we are observing them as they were in the past, and their active phase has since ended. This aligns with the understanding that quasars were more common in the early universe when conditions were different, and they have since "burned out" or evolved into other types of galactic nuclei.

What Is Believed to Be the Status of Quasars in the Present