Question

Using the virial theorem, explain why there is a need to postulate the existence of dark
matter.

Answer 1

Answer on question #54988, Physics / Astronomy — Astrophysics

Question Using the virial theorem, explain why there is a need to postulate the existence of dark matter.

Solution The virial theorem tells us that for gravitationally bound systems the potential energy of every element in average must be twice their kinetic energy. Zwicky in 1930-s has discovered that for galaxies and cluster of galaxies it is not true. The kinetic energies of elements of these systems are much higher then they should be. So, if we want them to be gravitationally bound, we must assume there is much more mass to gravitate and make potential energy large too. But this mass is invisible for us for some reasons, so it is called dark matter.