Introduction to Cosmology Ryden · Problem 6.6

Measuring Cosmological Parameters

Physics — Astrophysics · quasar-variability-angular-size

Problem

You observe a quasar at a redshift z=5.0z = 5.0, and determine that the observed flux of light from the quasar varies on a timescale δt0=3\delta t_0 = 3 days. If the observed variation in flux is due to a variation in the intrinsic luminosity of the quasar, what was the variation timescale δte\delta t_e at the time the light was emitted? For the light from the quasar to vary on a timescale δte\delta t_e, the bulk of the light must come from a region of physical size R≤Rmax⁡=c(δte)R \leq R_{\max} = c(\delta t_e). What is Rmax⁡R_{\max} for the observed quasar? What is the angular size of Rmax⁡R_{\max} in the Benchmark Model?

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