Rotation Curves

There is however some stronger evidence and ways to find out. Simply, because they provide mote reliable data and could be done for a larger number of galaxies. This happened in the 1970’s when people started measuring what is known as rotation curves for galaxies.

It is a known fact that galaxies spin around their centre. Like the planets orbiting the Sun. Just like planets orbiting the Sun, they too follow Kepler’s Law for orbits around the centre. Kepler’s Laws state that the rotational velocity around the centre depends only on the distance to the centre, and the total mass that is contained within the orbit.

Therefore, by finding the rotation velocities along a galaxy, one can ‘weigh’ the mass of the galaxy inside that orbit. The rotation speeds have been found to be very high and above what is expected. This indicates that there is a great deal of mass in the galaxy that we cannot see. This seems to be the case for many spiral galaxies, just like our own one. The same results keep coming up. Here is the strongest evidence that dark matter exists, as something that we cannot see is causing the mass.