Adapted from D. M. Mihalas and J. J. Binney, Galactic Astronomy , 2d ed.
All stars convert some hydrogen to helium.
Stars will lose part of their mass to the interstellar medium through stellar winds and outbursts like nebulae and novae. The evolutionary process for stars might be more exotic than once thought. General Features of Our Galaxy Large, flattened, disk-shaped Approximately 400 billion stars. Two spiral arms, extending from opposite sides, wrap around the nucleus in such a fashion that they trail as the galaxy rotates. Stars are most numerous in the nucleus and their numbers decline outward through the disk.