The stars we see in our night sky are not all the same, though they look very similar to our limited view. Some of the stars we see are actually planets, while other points of light might even represent stars that have died long before their light reaches us. Plus, stars themselves come under several categories and interesting names according to their properties.
A white dwarf is a small star which gives out white light. This is mainly because of its intense heat. Stars of this kind are immensely heavy for their size. According to astronomers, an average white dwarf star, though no larger than the Earth, is believed to weigh nearly 50,000 times as much as our planet. However, its density is around half that of the Sun, making it about 200,000 times more dense than the planet Earth. This makes them among the densest forms of matter known to us, second only to neuron stars.
In such a star, terrific heat and pressure is thought to break down the nature of the atom. This means that its parts, instead of reserving to themselves a space vastly greater than their own bulk, are crowded closely together. As a result, the heat at the center of a White Dwarf may be anything up to fifty times that at the center of the Sun.
White dwarf stars are also those that were previously like our Sun. However, their nuclear fuel was exhausted; when the nuclear burning stage was nearly at an end, the star expelled almost all of its external matter and created a planetary nebula. This resulted in just the white-hot core of this star remaining. The temperature of this core could be more than 100,000 Kelvin.
Eventually, over a billion years or thereabout, a white dwarf star could also cool down. This process might take a longer time if there’s a nearby star where the white dwarf can attract matter.
Since a white dwarf cannot create its own internal pressure, its gravity compacts its matter inward. Thus, even its electron are all forced together. Usually, identical electrons wouldn’t ever be at the same energy level with each other. Electrons can spin in just two ways, so only two opposite-spinning electrons can usually occur at one energy level. For white dwarfs, though, the density is so much that it results in a degenerate gas. When a star becomes degenerate, gravity simply cannot compress it any longer, as there’s no more space to occupy according to quantum mechanics. These quantum mechanical principles help to prevent the complete collapse of the white dwarf.
Degenerate matter has several unique properties. For instance, when a white dwarf has more mass, it actually become smaller. The more mass there is, the more its electrons squeeze together. This is necessary in order to maintain the outward pressure required for supporting the mass.
Still, there is a limit to the mass of a white dwarf star. According to the astrophysicist Subrahmanyan Chandrasekhar, this limit is around 1.4 time the Sun’s mass. This is also called the Chandrasekhar limit.
Since the white dwarf has a surface gravity that’s about 100,000 times stronger than Earth’s, it results in a very curious kind of atmosphere. Here, the heavy atoms sink and leave the lighter ones at its surface. As a result, some of the white dwarf stars may have atmospheres that consist solely of helium or pure hydrogen. These are the lightest elements we know of. The gravitational pull also means that the atmosphere is quite a thin layer. If this same phenomenon was on Earth, the atmosphere’s limit will be below our highest skyscrapers.
One hypothesis states that many white dwarf stars have a 50-kliometre crust below their atmosphere. Below this, there’s a network of oxygen and carbon atoms in a crystallized from. Diamonds, as we know, are just compressed and crystallized carbon, so a white dwarf might have a lot of diamonds on them.