2013

The Hubble constant from one galaxy

Round: Theory
Points: 10
Level: Bronze
Taught in: Section 13.1

Adapted from IOAA 2013 (Volos), theory problem 5. We have restated it in our own words and kept the original data. The solution was last checked on 21 October 2026.

The spectrum of a galaxy whose distance has been measured as 41.67 Mpc shows the Balmer Hα line, which is at 656.3 nm in the laboratory, shifted to 662.9 nm.

(a) Use this to find the Hubble constant. [7 points]

(b) From your result, estimate the Hubble time. [3 points]

I solved it without the solution

Answer(a) $H_{0} = 72.4$ km/s/Mpc. (b) The Hubble time is about 13.5 billion years.

This problem also appears among the olympiad problems of Section 13.1, The expanding universe, which teaches the ideas it uses. Equation and figure numbers refer to the course.