How Do We Know That AGNs Have Sizes on the Order

question 26

Multiple Choice

How do we know that AGNs have sizes on the order of our Solar System?

• A) Quasars and Seyfert galaxies are stellar-like sources.
• B) Their brightness varies by factors of a few.
• C) The emission lines in their spectra show gas rotating at speeds of thousands of km/s.
• D) Their brightness varies on timescales ranging from hours to a day.
• E) We can measure their angular size, which gives us the physical size when we know the distance.

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