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A typical white dwarf has a density of between 10 4 and 10 7 g/cm 3. White dwarfs are composed of one of the densest forms of matter known, surpassed only by other compact stars such as neutron stars and the hypothetical quark stars. [29] [30] White dwarfs were found to be extremely dense soon after their discovery.
Comparison of a 10 km radius neutron star (top left corner) and a 6000 km radius white dwarf, the latter roughly the size of Earth. Neutron stars have overall densities of 3.7 × 10 17 to 5.9 × 10 17 kg/m 3 (2.6 × 10 14 to 4.1 × 10 14 times the density of the Sun), [a] which is comparable to the approximate density of an atomic nucleus of 3 ...
where measures the density of white dwarf, is the non-dimensional radial distance from the center and is a constant which is related to the density of the white dwarf at the center. The boundary η = η ∞ {\displaystyle \eta =\eta _{\infty }} of the equation is defined by the condition
First solitary white dwarf Van Maanen 2: 1917 Van Maanen's star is also the nearest solitary white dwarf [5] First white dwarf with a planet WD B1620−26: 2003 PSR B1620-26 b (planet) This planet is a circumbinary planet, which circles both stars in the PSR B1620-26 system [6] [7] First singular white dwarf with a transiting object WD 1145+017 ...
White dwarfs arise from the cores of main-sequence stars and are therefore very hot when they are formed. As they cool they will redden and dim until they eventually become dark black dwarfs. White dwarfs were observed in the 19th century, but the extremely high densities and pressures they contain were not explained until the 1920s.
The surface gravity of a white dwarf is very high, and of a neutron star even higher. A white dwarf's surface gravity is around 100,000 g ( 10 6 m/s 2 ) whilst the neutron star's compactness gives it a surface gravity of up to 7 × 10 12 m/s 2 with typical values of order 10 12 m/s 2 (that is more than 10 11 times that of Earth).
An exoplanet orbits PSR B1620-26 and its white dwarf companion (see below) in a circumbinary orbit. HD 49798: 1,600 White dwarf: One of the smallest white dwarf stars known. [14] ZTF J1901+1458: 1,809 Currently the most massive white dwarf known. [15] Janus: 3,400 A white dwarf with a side of hydrogen and another side of helium. [16] Wolf 1130 ...
The supposed planetesimal, WD 1145+017 b, [13] with a 4.5 hour orbit, is being ripped apart by the star and is a remnant of the former planetary system that the star hosted before becoming a white dwarf. [8] [9] It is the first observation of a planetary object being shredded by a white dwarf. Several other large pieces have been seen in orbit ...