Worked Example 01

The Question

A star has recently been discovered travelling in a circular orbit around our galaxy (the Milky Way). It’s orbit is 80 kilo-parsecs out, and it is traveling at a speed of 320 km/s. Deduce the mass of our galaxy from this. Compare your answer to the mass of everything we can see in our galaxy (1.2x10⁴² kg). A kilo-parsec is 1000 parsecs, and a parsec is 3.1x10¹⁶ m.

The Answer

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