Dark energy and the rotation curve of spiral galaxies

[Apashanka]

Recently I have studied that from the rotation curve of spiral galaxies, the nearly constt. behaviour of velocity of the stars situated far away from the central core suggests mass(r) ~ r ,rather than 1/√r as expected.
Are there any other theory which proves the existence of dark energy ??

 

[Janus]

Dark matter is the proposed explanation for galaxy rotation curves. Dark energy is the name given to what is driving the apparent accelerated expansion of the universe. These are two separate things and their only relationship is the word "dark" in their titles.

There are a number of observations that support the dark matter hypothesis. Gravitational lensing shows light bending around galaxies in a manner consistent with that model. The Bullet cluster observation shows us the result of two galaxy clusters colliding. It includes a region where we measure gravitational lensing, but no visible matter to cause it. This is consistent with dark matter being "knocked loose" during the collision.
Recently there have been discoveries of galaxies that behave as if they have little to no dark matter. This is, in fact, evidence supporting the dark matter model.( With other explanations for galaxy rotation curves, such as modified gravity theories, One would expect to see the effect in all galaxies, where as there is nothing that says that every galaxy must have dark matter.