## The Hidden Lives of Galaxies - Weighing a Galaxy

## Activity #6d

Weighing a Galaxy

Using Newton's Law for gravity, we can determine the mass of an object by measuring the motion of other bodies around it. We can show this by applying Newton's Law of motion to bodies orbiting around another body. We start with Newton's Second Law

^{2}= mv

^{2}/r,

^{2}.

^{2}r/G.

^{-11}m

^{3}/kg-s

^{2}.

Apply this equation fo three of the planets in our solar system, given in the table below.

Planet Distance from Sun (km) Velocity (km/s) Mass (kg) Earth 1.5 x 10 ^{8}29.8 Jupiter 7.8 x 10 ^{8}13.1 Neptune 4.5 x 10 ^{9}5.4 What do you notice about the values of the Mass?__________________

Wat would you conclude the mass of the Sun to be?___________________

Now apply this equation to the galaxy F563-1. Determine the mass M using the equation and the velocity at various distances rom the center of the galaxy given in the table below. Each of these resulting mass values gives mass enclosed within that distance. [Note that 1 kiloparsec (kpc) = 3.1 x 10

^{19}meters]

Distance (kpc) | Velocity (km/s) | Mass (kg) |
---|---|---|

5.0 | 95.0 | |

10.0 | 110.0 | |

15.0 | 110.0 |

What do you notice about the values of the mass as the distance increases?

_____________________________________________________________

_____________________________________________________________

What would you conclude the mass of the galaxy to be? _____________________________________________________________

How much more massive is this galaxy than our Sun? _____________________________________________________________