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.
The Sun and the Solar System are about 20 galactic years old. The angular distance measured in the central plane of the disk, starting with the Galactic center and measuring along the Milky Way. The angular distance above and below the central plane of the Milky Way. One means of determining the Galaxy's rotation is to use a frame of reference outside of the Galaxy, i.e., distant galaxies. Within 300 ly of the Galactic center, the central regions rotate like a solid wheel so that the orbital velocities increase from the center outward.