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Unformatted text preview: Astronomy 160: Frontiers and Controversies in Astrophysics Homework Set # 9 Solutions 1) Some preliminary exercises in dealing with BCGs: a) Assuming that the light from a BCG is made up of light from stars like the Sun, how many stars does a BCG contain? Recall that the absolute magnitude of the Sun is +5. We can compare the absolute magnitude of the Sun to the absolute magnitude of a BCG in order to find the ratio of their luminosities. We can do this via the magnitude equation: M BCG- M =- 2 . 5 log L BCG L- 25- 5 =- 2 . 5 log L BCG L- 30 =- 2 . 5 log L BCG L 12 = log L BCG L 10 12 = L BCG L This means that the BCG is 10 12 times more luminous than the Sun. Assuming that all of the stars in the BCG are like the Sun, this means that there must be 10 12 Sun-like stars in the BCG. b) If a BCG is observed to have an apparent magnitude of 10, what is its redshift z ? The redshift of an object is just an effect of the object moving away from us....
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This note was uploaded on 02/06/2012 for the course BENG 100 taught by Professor Marksaltzman during the Spring '08 term at Yale.
- Spring '08