# Relationship between mass and radius white dwarf stars for kids

### Newest 'white-dwarfs' Questions - Physics Stack Exchange

The white dwarf continues to gobble up matter from the other star until eventually The more mass a white dwarf has, the greater the gravity, the more its They have a radius that's typically around times smaller than our. Advertiser Links . According to theory, a typical white dwarf can shrink its radius by several This simplified graphic displays the different evolutionary pathways stars can take depending on their mass. Astronomy for Kids. Most stars in the universe will eventually burn off all of their hydrogen and become dead husks called white dwarfs. White dwarfs contain approximately the mass of the sun but have white dwarf has a smaller radius than its less massive counterpart. In her free time, she homeschools her four children.

If the star is allowed to rotate nonuniformly, and viscosity is neglected, then, as was pointed out by Fred Hoyle in[52] there is no limit to the mass for which it is possible for a model white dwarf to be in static equilibrium. Not all of these model stars will be dynamically stable. This matter radiates roughly as a black body. This enables the composition and structure of their atmospheres to be studied by soft X-ray and extreme ultraviolet observations.

As was explained by Leon Mestel inunless the white dwarf accretes matter from a companion star or other source, its radiation comes from its stored heat, which is not replenished.

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White dwarfs have an extremely small surface area to radiate this heat from, so they cool gradually, remaining hot for a long time. Since the white dwarf has no energy sink other than radiation, it follows that its cooling slows with time. The rate of cooling has been estimated for a carbon white dwarf of 0. After initially taking approximately 1.

### White Dwarfs: Compact Corpses of Stars

Once we adjust for the selection effect that hotter, more luminous white dwarfs are easier to observe, we do find that decreasing the temperature range examined results in finding more white dwarfs. New research suggests that the Milky Way's preponderance of positrons could come from a specialized type of supernova from colliding low-mass white dwarfs — an explosion that is difficult to detect, but rich in an isotope that generates this kind of antimatter. If the white dwarf is part of a binary system, it may be able to pull material from its companion onto its surface.

Increasing the white dwarf's mass can have some interesting results. One possibility is that the added mass could cause it to collapse into a much denser neutron star. A far more explosive result is the Type 1a supernova.

As the white dwarf pulls material from a companion star, the temperature increases, eventually triggering a runaway reaction that detonates in a violent supernova that destroys the white dwarf. This process is known as a "single-degenerate model" of a Type 1a supernova. Star Explosions Explained Infographic ] Inresearchers were able to closely observe the complex shells of gas surrounding one Type 1a supernova in fine detail.

This process is known as a "double-degenerate model" of a Type 1a supernova. At other times, the white dwarf may pull just enough material from its companion to briefly ignite in a nova, a far smaller explosion. Because the white dwarf remains intact, it can repeat the process several times when it reaches that critical point, breathing life back into the dying star over and over again. This article was updated on Oct.

Table 7 presents a comparison of mass measurements for various stars in our sample. Mlog is our recalculated spectroscopic mass using published surface gravities and the radii from Tables 35and 6.

Mlog does not rely on the mass-radius relation. Mgr is the gravitational redshift mass, and Mastro is the astrometric mass. CD is a well-studied CPM white dwarf.

Later work Vennes et al. In any case, the spectroscopic mass is significantly lower than Mgr. These results are consistent with the arguments of BSLassuming CD actually has a thick hydrogen surface layer. Figure 4 further supports this conclusion. The thick surface layer model predicts a mass of 0. Based on these results, we suggest that CD has a thick hydrogen surface layer.

A similar case can be argued for Wolf A, where Mspec is again significantly lower than either Mgr or Mlog. On the other hand, Shipman et al.

### Astronomers weigh a white dwarf using gravitational lensing | promovare-site.info

Thick hydrogen atmosphere models predict a mass of 0. Therefore, we are reasonably confident that 40 Eri B has a thin hydrogen atmosphere.

Combined with CD and Wolf A, these findings support other investigations Shipman arguing that the ratio of DAs to non-DAs at cooler temperatures indicates that DAs do not have the same envelope structure but span a range of hydrogen layer thicknesses from to M.

Photospheric Helium A second possible consideration is the undetected presence of helium. BSL convincingly demonstrates that at temperatures below 12, K, large amounts of spectroscopically invisible helium brought to the surface by convection can produce pressure effects that are indistinguishable from increased surface gravity.

In essence, cool DA white dwarfs with large surface gravities can be interpreted as helium-rich stars with normal masses.

All of the field stars, with the exception of G, are above 15, K. The key to distinguishing helium's presence may come from a comparison of gravitational and spectroscopic masses.

## Astronomers weigh a white dwarf using gravitational lensing

The non-LTE core of H commonly used in gravitational velocity measurements is least affected by pressure shifts of all the hydrogen lines. Its gravitational mass 0.

However, Mlog argues that this white dwarf is more massive than Sirius B. While it would be nice to have another massive white dwarf to help pin down the high-mass end of the mass-radius relation, this result instead suggests that an additional source of pressure, probably helium, is mimicking increased surface gravity. For these two objects, Mlog is lower than Mgr. G is the brightest and closest known DA nonradial pulsator.