If a Seyfert galaxy's nucleus varies in brightness on the timescale of 10 hours, then approximately what is the size of the emitting region?
A) 20 AU
B) 30 AU
C) 50 AU
D) 70 AU
E) 120 AU

Question

Quizplus · Accepted Answer

The timescale of 10 hours suggests that the emitting region is relatively small, since larger regions would take longer to vary in brightness. Seyfert galaxies are believed to harbor supermassive black holes in their nuclei, which can power the observed emission through accretion of surrounding material. The size of the accretion disk around the black hole is a natural candidate for the emitting region, and estimates based on modeling suggest disk sizes of tens to hundreds of astronomical units (AU). Of the choices given, D) 70 AU is closest to this expected range.

If a Seyfert Galaxy's Nucleus Varies in Brightness on the Timescale