The world needs a new source of energy, an unspillable source.

When a large star has spent all its nuclear energy it finally contracts due to its own gravity and becomes?

When a large star has spent all its nuclear energy it finally contracts due to its own gravity and becomes a dense small object called a neutron star. Many such stars are found to be rotating with a high speed. How can you account for this high rate of rotation particularly when most stars like our sun are rotating very slowly?