When we analyze the universe and all the celestial bodies that compose it, the first thing we must are the stars. The stars have an evolution different stages through which it passes from when it is created until it is destroyed. The last final stage that has evolution of a star is known as White dwarfThese are small, compact stars that have the ability to spin rapidly. They have a beam that can be perfectly compared to that of our planet, and they are stars that eventually collapse.
In this article we are going to tell you all the characteristics, origin and composition of the white dwarf.
Key features
It is a stellar remnant that is formed when a star that has a lower mass has used up all the nuclear fuel it had. A white dwarf is characterized by being very hot and small but with little luminosity. They are considered as stars of low planetary mass. It can be said that a white dwarf is the result of what is going to happen to our sun. When our sun runs out of fuel to carry out nuclear fusion, it will turn into these types of stars.
Near the end of a star's lifespan, we find a reduction in nuclear burning. This type of star expels most of its material to the outside, giving rise to a planetary nebula, as happens in the life cycle of other stars. When all its material has been released, the nebula is generated, and only the star's hot core remains. This core is what becomes the white dwarf. temperatures that can exceed 100.000 degrees KelvinUnless the white dwarf accumulates matter from nearby stars, it will likely cool down over the next billion years.
As expected, they are processes that do not occur on a human scale so it cannot be seen with the naked eye.
Properties of the white dwarf
Let's see what are some of the main properties that these types of stars have in their final stage:
- The most typical white dwarf it is about half the size of our sun. It is slightly larger than planet Earth.
- They are stars of a very small size but high temperature and the mass is comparable to that of the sun. The fact that they looked white is due to their temperature.
- They represent the final phase of a star's life and are similar to the sun. We know there are many types of stars, each with different characteristics. You can learn more about these celestial bodies by visiting our article on .
- They are considered within the group of bodies densest of matter that is in all the space. They are only surpassed by neutron stars, such as those observed in the supernova explosion.
- Because it cannot create internal pressure, gravity compacts matter inward to crush even all the electrons with which it is created.
- By not having thermonuclear reactions in its core, it does not have any kind of power source. This causes it to gradually compress on its own weight.
When we analyze a white dwarf in its entire composition, we see that it is made up of atoms in a plasma state. The atoms are responsible for emitting only thermal energy that is stored. This is the reason why that this type of stars has a fairly weak luminosity. When the white dwarf ends with the fusion of hydrogen, it expands like red giants and they fuse helium into carbon and oxygen. This carbon and oxygen serve for its nucleus. Above them we can find a layer of degenerated hydrogen and helium that give shape to a kind of atmosphere that it has.
Formation of a white dwarf
Let's see what are the main steps that the formation of a white dwarf follows. It is said that all stars have different stages and that they end up dying. In this case, at the end of evolution they transform into this type of starThese are those that have exhausted all the hydrogen they have and used as nuclear fuel. The fusion that occurs in the star's core produces heat and pressure toward the outside. This pressure is balanced by the gravitational force generated by the star's mass.
Once all the hydrogen fuel has been used, nuclear fusion ends and begins to slow down. This causes the star's gravity to collapse. As a star condenses and compacts due to the action of gravity, it burns hydrogen, causing the outer layers of the star expand outward. Therefore, we first see that before being a white dwarf it is a red giant, like those found in the constellation of orionBecause of its large size, heat expands and its surface temperature becomes cooler. However, its core remains hot.
These stars are responsible for converting the helium in their core into various heavier elements, such as carbon. They then expel the material from their outer layers, creating a gas envelope. This gas envelope is considered a small atmosphere. The core continues to heat up and contracts until it forms the white dwarf.
Types and curiosities
Let's see what are the different types of white dwarf that exist:
- dA: are white dwarfs that only have Balmer lines and no metals present.
- dB: in this type there are no metals present.
- AD: they have a continuous spectrum, and few or none of them have a visible line.
- do: They contain helium or hydrogen.
- dZ: they have only a few metal lines.
- dQ: they have characteristics of carbon either atomic or molecular in any part of the spectrum.
Among the curiosities of these stars is that they are excessively dense despite their radius being smaller than the sun's. These bodies have the same solar density. During the cooling process of the stars, a gaseous material known as planetary nebula. Here we see that the stellar nucleus has a higher density due to gravity.
I hope that with this information you can learn more about the white dwarf and its characteristics.