M104 is a galaxy seen edge-on.

This galaxy is linked with the discovery of the "red shift" and the mistery of the expanding universe. Investigation of the radial velocities of the galaxies was begun at Lowel observatory in 1912, before the true nature of such objects was known. The Sombrero was found to show a red shift of nearly 1100 km/s. This enormous velocity, exceeding anything known at the time, made it seem very unlikely that such a "nebula" could be a local gas cloud in the Milky Way system, and offered strong support for the "Island Universe" theory.

Burnham's Celestial Handbook