Astrophysics (index)about

white dwarf

(degenerate dwarf)
(stellar remnant of mostly electron-degenerate matter)

A white dwarf is a star past its main-sequence thermonuclear stage that has expelled its exterior and only the core remains. The remaining mass must be sufficiently low that electron degeneracy prevents further collapse into a neutron star. As the remains of a star, it is classified as a stellar remnant. They are small and massive, e.g., the size of Earth with the mass of the Sun, and a density on the order of 100,000 times that of Earth:

Mass range .17 to 1.33 Solar masses
Radius range 1300 to 15000 km
Bulk density range 103-107 g/cc
Luminosity range about .1 Solar for brightest (at the beginning of their life)

They generally transfer their energy to the surface by conduction (interaction of particles) rather than radiative transfer. Most are oxygen and carbon but under some conditions can have neon, magnesium, or helium. The limit on their mass is about 1.4 solar masses (the Chandrasekhar limit) and if an existing white dwarf grows beyond that, e.g., due to mass transfer from a companion, a type Type Ia supernova can result. White dwarfs begin at the temperature left over form the main sequence, at which time they can be far hotter at the surface than the Sun, then they cool very slowly. The term black dwarf refers to the theoretical state of a white dwarf cooled to the degree that it emits no appreciable EMR, but the universe is not old enough for any to be near that state.

Types:

Some white dwarf spectral types (e.g., "DBV"):

DAJust H spectral lines
DBJust He I lines
DCNo lines
DOIncludes H II lines
DZmetal lines
DQCarbon lines
DXUnclear

Optional letter designating other features:

PPolarized
HMagnetism but no polarization
Eemission lines
VVariable

(star type,degeneracy)
http://en.wikipedia.org/wiki/White_dwarf

Referenced by:
asymptotic giant branch (AGB)
Black Widow Pulsar (B1957+20)
black hole binary (BHB)
calcium-rich gap transient
Chandrasekhar limit
compact object (CO)
cataclysmic variable star (CV)
dwarf nova
dynamical instability
electron degeneracy
giant star
H-R diagram (HRD)
J1713-0747
low mass star
luminosity class
main sequence star
neutron star
nova
planetary nebula (PN)
post main sequence star
Procyon
rare designator prefixes
supernova (SN)
stellar demographics
stellar evolution
stellar remnant
stellar rotation
Sun
symbiotic binary
Tolman-Oppenheimer-Volkoff limit (TOV)
Type Ia supernova
Urca process
variable star
Villanova White Dwarf Catalog

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