![]() ![]() This is exactly what you would expect for a spinning ball of charge, but if you go through the math, you find that it can't possibly work. I say "as if" there, because they are not literally spinning balls of charge, because the spin angular momentum associated with fundamental particles has some properties that are very strange, and completely unlike the behavior of spinning basketballs, or gyroscopes, or figure skaters, or whatever your favorite example of a system with angular momentum is.įirst, though, how can we say with certainty that these aren't literally spinning balls of charge? Well, in addition to their angular momentum, the fundamental particles also have a magnetic moment associated with them, which is to say they behave like tiny little bar magnets with a north and south pole. Electrons, and all other fundamental particles, have a property known as "spin." This is an intrinsic angular momentum associated with the particles, as if they were little spinning balls of charge. I'll put a clip of the final version of the game at the end of this post.) (That's an early version of SteelyKid's new favorite game. As a bonus, this gives me the opportunity to do the dorkiest thing anyone has ever done with a cute-toddler video, namely this one: Introductory level article on this topic.The subject of the "spin" of the electron comes up again and again, so as pointed out in a comment, I really ought to do a post explaining what it is and how it works.Since a diamond is just crystallized carbon, one might make the comparison between a cool carbon/oxygen white dwarf and a diamond. At the bottom of this crust is a crystalline lattice of carbon and oxygen atoms. Scientists hypothesize that there is a crust 50 km thick below the atmosphere of many white dwarfs. If this occurred on Earth, the top of the atmosphere would be below the tops of skyscrapers. Also, gravity pulls the atmosphere close around it in a very thin layer. Some white dwarfs have almost pure hydrogen or helium atmospheres, the lightest of elements. The heavier atoms in its atmosphere sink, and the lighter ones remain at the surface. With a surface gravity of 100,000 times that of Earth, the atmosphere of a white dwarf is very strange. Subrahmanyan Chandrasekhar discovered this limit to be 1.4 times the mass of the Sun. This is appropriately known as the "Chandrasekhar limit." However, there is a limit on the amount of mass a white dwarf can have. 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. For example, the more massive a white dwarf is, the smaller it is. So our white dwarf survives, not by internal fusion, but by quantum mechanical principles that prevent its complete collapse.ĭegenerate matter has other unusual properties. Once a star is degenerate, gravity cannot compress it any more, because quantum mechanics dictates that there is no more available space to be taken up. ![]() For gravity to compress the white dwarf further, it must force electrons where they cannot go. This is referred to as a "degenerate" gas, meaning that all the energy levels in its atoms are filled up with electrons. ![]() But in a white dwarf, the density is much higher, and all of the electrons are much closer together. In a normal gas, this isn't a problem because there aren't enough electrons floating around to fill up all the energy levels completely. This is what's known in physics as the Pauli Exclusion Principle. Since there are only two ways an electron can spin, only two electrons can occupy a single energy level. In normal circumstances, identical electrons (those with the same "spin") are not allowed to occupy the same energy level. from the release of energy from fusion, because fusion has ceased), gravity compacts the matter inward until even the electrons that compose a white dwarf's atoms are smashed together. What's inside a white dwarf?īecause a white dwarf is not able to create internal pressure (e.g. This makes white dwarfs one of the densest collections of matter, surpassed only by neutron stars. That means a white dwarf is 200,000 times as dense. An Earth-sized white dwarf has a density of 1 x 10 9 kg/m 3. Earth itself has an average density of only 5.4 x 10 3 kg/m 3. An Artist's conception of the evolution of our Sun (left) through the red giant stage (center) and onto a white dwarf (right).Ī typical white dwarf is half as massive as the Sun, yet only slightly bigger than Earth. ![]()
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