Sirius B, a white dwarf star, is difficult to observe in the glare from the A-type star Sirius A
Spectral type D (often followed by an optional letter defining secondary spectral features)
Small, faint, very dense, hot star near the end of its life; the cooling naked cores of the most highly evolved stars which have mostly consumed their fusionable elements and undergone gravitational collapse; all that remains after a red giant star loses its outer layers.
The nuclear core is depleted, and the star consists mostly of carbon. This makes them quite valuable to star miners and developers, since it is often cheaper to extract large quantities of carbon from such a star then through alchemics or from asteroids. An average white dwarf is about the size of a large terrestrial class planet.
More massive white dwarfs are usually less luminous because their higher gravity contracts the stars, reducing the surface area. They are chemically differentiated into two broad groups: hydrogen rich (e.g. Sirius B) and helium rich (e.g. HZ-29). Colour does not correlate with temperature as each type spreads out across the whole temperature sequence from early O-type to M equivalents. All white dwarfs are necessarily less massive than the Chandrasekhar Limit, approximately 1.4 Msol. Being insufficiently massive to collapse into a neutron star, further collapse is prevented by electron degeneracy pressure.