Why is there a mass limit for white dwarf stars? This is because the more mass a white dwarf has, the more its electrons must squeeze together to maintain enough outward pressure to support the extra mass. However, there is a limit on the amount of mass a white dwarf can have.
Why is there an upper limit to the mass of white dwarfs?
Why is there an upper limit to the mass of a white dwarf? The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons.
Why is a white dwarf star so dense?
The material in a white dwarf no longer undergoes fusion reactions, so the star has no source of energy. As a result, it cannot support itself by the heat generated by fusion against gravitational collapse, but is supported only by electron degeneracy pressure, causing it to be extremely dense.
How does mass affect the speed of electrons in a white dwarf?
To interpret this result, observe that as we add mass to a white dwarf, its radius will decrease, so, by the uncertainty principle, the momentum, and hence the velocity, of its electrons will increase.
How big is the magnetic field of a white dwarf star?
It is thought to have a surface field of approximately 300 million gauss (30 kT). : §8 Since 1970 magnetic fields have been discovered in well over 200 white dwarfs, ranging from 2 × 103 to 10 9 gauss (0.2 T to 100 kT).
Why is there a limit on the mass of a white dwarf?
Using Albert Einstein's special theory of relativity and the principles of quantum physics, Chandrasekhar showed that it is impossible for a white dwarf star, which is supported solely by a degenerate gas of electrons, to be stable if its mass is greater than 1.44 times the mass of the Sun.
What happens when you add too much mass to a white dwarf?
If a white dwarf does, however, gain enough mass through this process, it will collapse in a supernova type I. The supernova is probably too powerful to leave a neutron star behind; the white dwarf is blown apart. On the other hand, a neutron star which accretes too much mass will indeed collapse into a black hole.
Do white dwarf stars have a lot of mass?
A typical white dwarf is about as massive as the Sun, yet only slightly bigger than the Earth. This makes white dwarfs one of the densest forms of matter, surpassed only by neutron stars and black holes. Medium mass stars, like our Sun, live by fusing the hydrogen within their cores into helium.
What happens if a white dwarf exceeds 1.4 solar masses?
A white dwarf star is in balance between gravity and degeneracy pressure, but if the mass is too large (greater than 1.4 solar masses, called the Chandrasekhar limit), the degeneracy pressure is not adequate to hold up the star, and the star collapses.
What would happen if mass is added to a 1.4 solar mass white dwarf?
What would happen if mass is added to a 1.4 solar mass white dwarf? The star would eventually become a black hole.
Can a white dwarf have a mass of 10 solar masses?
The Chandrasekhar limit of around 1.4 solar masses is the theoretical upper limit to the mass a white dwarf can have and still remain a white dwarf. Beyond this mass, electron pressure can no longer support the star and it collapses to an even denser state – either a neutron star or a black hole.
Can a star of 2.5 solar masses ever become a white dwarf?
Even for these more massive stars, however, if the residual mass in the core is less than 1.4 solar masses (the Chandrasekhar limit), the stellar remnant will become a white dwarf.
What causes Chandrasekhar limit?
Due to the pressure of electron degeneration, the white dwarf stars oppose its gravitational collapse. Chandrasekhar limit is established at a point when the mass at which the pressure from the degeneration of electrons is not able to balance the self-attraction of the gravitational field.
Overview
A white dwarf, also called a degenerate dwarf, is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: its mass is comparable to that of the Sun, while its volume is comparable to that of Earth. A white dwarf's faint luminosity comes from the emission of residual thermal energy; no fusion takes place in a white dwarf. The nearest known whi…
Discovery
The first white dwarf discovered was in the triple star system of 40 Eridani, which contains the relatively bright main sequence star 40 Eridani A, orbited at a distance by the closer binary system of the white dwarf 40 Eridani B and the main sequence red dwarf 40 Eridani C. The pair 40 Eridani B/C was discovered by William Herschel on 31 January 1783. In 1910, Henry Norris Russell, Edward Charles Pickering and Williamina Fleming discovered that, despite being a dim star, 40 Eridani B w…
Composition and structure
Although white dwarfs are known with estimated masses as low as 0.17 M☉ and as high as 1.33 M☉, the mass distribution is strongly peaked at 0.6 M☉, and the majority lie between 0.5 and 0.7 M☉. The estimated radii of observed white dwarfs are typically 0.8–2% the radius of the Sun; this is comparable to the Earth's radius of approximately 0.9% solar radius. A white dwarf, then, packs m…
Variability
Early calculations suggested that there might be white dwarfs whose luminosity varied with a period of around 10 seconds, but searches in the 1960s failed to observe this. The first variable white dwarf found was HL Tau 76; in 1965 and 1966, and was observed to vary with a period of approximately 12.5 minutes. The reason for this period being longer than predicted is that the variability of HL Tau 76, like that of the other pulsating variable white dwarfs known, arises from …
Formation
White dwarfs are thought to represent the end point of stellar evolution for main-sequence stars with masses from about 0.07 to 10 M☉. The composition of the white dwarf produced will depend on the initial mass of the star. Current galactic models suggest the Milky Way galaxy currently contains about ten billion white dwarfs.
If the mass of a main-sequence star is lower than approximately half a solar mass, it will never b…
Fate
A white dwarf is stable once formed and will continue to cool almost indefinitely, eventually to become a black dwarf. Assuming that the Universe continues to expand, it is thought that in 10 to 10 years, the galaxies will evaporate as their stars escape into intergalactic space. White dwarfs should generally survive galactic dispersion, although an occasional collision betwee…
Debris disks and planets
A white dwarf's stellar and planetary system is inherited from its progenitor star and may interact with the white dwarf in various ways. Infrared spectroscopic observations made by NASA's Spitzer Space Telescope of the central star of the Helix Nebula suggest the presence of a dust cloud, which may be caused by cometary collisions. It is possible that infalling material from this may cause …
Habitability
It has been proposed that white dwarfs with surface temperatures of less than 10,000 Kelvins could harbor a habitable zone at a distance of c. 0.005 to 0.02 AU that would last upwards of 3 billion years. This is so close that any habitable planets would be tidally locked. The goal is to search for transits of hypothetical Earth-like planets that could have migrated inward and/or formed there. As a white dwarf has a size similar to that of a planet, these kinds of transits woul…