Class M stars are by far the most common. About 76% of the main-sequence stars in the Solar neighborhood are class M stars.
In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Showing the relationship between the stars’ luminosities versus their spectral classifications is done in the Hertzsprung-Russell diagram.
A protoplanetary disk is a rotating circumstellar disk of dense gas and dust surrounding a young newly formed star, a T Tauri star.
A debris disk is a circumstellar disk of dust and debris in orbit around a star. Debris disks have been found around both mature and young stars, as well as at least one debris disk in orbit around an evolved neutron star.
Bow shocks form the boundary between a magnetosphere and an ambient magnetized medium. This occurs when the magnetic field of an astrophysical object interacts with the nearby flowing ambient plasma.