Question

An AGN is observed to double in brightness over 7.7 days and then to grow dim again in the next 7.7 days. What is an upper limit to the probable size of the AGN?

______ AU

Answer 1

given

C = 3 x 10⁸ m/sec

= 3 x 10⁵ km/sec

$\Delta$ t = 7.7 days

= 7.7 x 24 hours

= 7.7 x 3600

$\Delta$ t = 27720 sec

size = C $\Delta$ t

= 3 x 10⁸ x 27720

= 8.316 x 10¹² m

we have 1 m = 6.6846 x 10^-12 AU

= 8.316 x 10¹² x 6.6846 x 10^-12

= 55.5891 AU

so the probable size of the A G N is 55.5891 AU.