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# Cosmology - Luminosity, Brightness, Speed of Recession

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If a galaxy has a luminosity of 6.6x10^39 W and a brightness measured as 1.25x10^-11 W m^-2, How far away is the galaxy in mega parsecs?

An absorption line of the element beryllium is observed in the spectrum of the galaxy above as lying 509.4 nm. What is the speed of the recession of the galaxy in km s^1 assuming that the speed of light is c = 3.00 x 10^5 km s^-1

And what is the value of the Hubble Constant?

##### Solution Summary

The expert examines luminosity, brightness and speed of recession for cosmology. The value of the hubble constant is determined. All the questions solved and explained step-by-step.

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(1) L = 6.6 * 10^39 W, b = 1.25 * 10^-11 W/m^2

b = L / (4 * pi * d^2)

4 pi d^2 = L / b

d^2 = L / (4 pi b)

d = sqrt [L / (4 pi b)]

d = sqrt [6.6 * 10^39 / (4 * pi * 1.25 * 10^-11)] = 4.20 * 10^49 m

Since 1 Mparsec = 3.262 * ...

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