|System:||HIP 21251 - All bodies|
|Distance to Sol:||437.84 ly|
|Distance To Arrival:||81,607 ls|
|Age:||1,010 Million years|
|Surface Temperature:||0 K|
|Orbital Period:||276,540.4 D|
|Semi Major Axis:||146.32 AU|
|Orbital Inclination:||45.71 °|
|Arg Of Periapsis:||42.61 °|
A white dwarf, also called a degenerate dwarf, is a stellar remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to that of the Sun, and its volume is comparable to that of Earth. A white dwarf's faint luminosity comes from the emission of stored thermal energy. The nearest known white dwarf is Sirius B, at 8.6 light years, the smaller component of the Sirius binary star. There are currently thought to be eight white dwarfs among the hundred star systems nearest the Sun. The unusual faintness of white dwarfs was first recognized in 1910. The name white dwarf was coined by Willem Luyten in 1922.
White dwarfs are thought to be the final evolutionary state of stars (including our Sun) whose mass is not high enough to become a neutron star - over 97% of the stars in the Milky Way. After the hydrogen–fusing period of a main-sequence star of low or medium mass ends, a star will expand to a red giant during which it fuses helium to carbon and oxygen in its core by the triple-alpha process. If a red giant has insufficient mass to generate the core temperatures required to fuse carbon, around 1 billion K, an inert mass of carbon and oxygen will build up at its center. After shedding its outer layers to form a planetary nebula, it will leave behind this core, which forms the remnant white dwarf. Usually, therefore, white dwarfs are composed of carbon and oxygen. If the mass of the progenitor is between 8 and 10.5 solar masses (M☉), the core temperature is sufficient to fuse carbon but not neon, in which case an oxygen–neon–magnesium white dwarf may form. Stars of very low mass will not be able to fuse helium, hence, a helium white dwarf may form by mass loss in binary systems.
Black holes are typically the stellar remnants of super massive stars of twenty solar masses or more, that have reached the end of their lives. Nuclear fusion has ceased, and the star collapsed to the most extreme point possible - where gravity was so extreme light can no longer escape. If matter should fall on to such a body, an extreme burst of gamma radiation will be emitted, but otherwise the body is only visible by the gravitational distortion in the vicinity. In many cases black holes can be seen emitting brightly in X-rays because of matter falling on to their surface from a companion body.