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 dwarf. They are small compact stars that have the ability to rotate rapidly. They have a ray that can be perfectly compared to that of our planet and they are stars that end up collapsing.
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 do nuclear fusion, it will become this type of star.
Near the end of the stage that a star has, we find a reduction in nuclear combustion. These types of stars expel most of all the material they have to the outside and gives rise to a planetary nebula. When it has released all its material, I generated the nebula, only the hot core of the star remains. This nucleus is what becomes the white dwarf with temperatures that can exceed 100.000 degrees Kelvin. Unless the white dwarf is in charge of accumulating matter from stars near it, it will most likely cool down over the next billions of 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 are those that represent the last phase of the life of a star that are similar to the sun. We know that there are many types of stars and each one has different characteristics.
- They are considered within the group of bodies densest of matter that is in all the space. They are second only to neutron stars.
- 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 star. They are those that have used up all the hydrogen they have and used as nuclear fuel. The fusion that happens in the core of the star produces heat and pressure towards its exterior. This pressure is responsible for balancing thanks to the force of gravity generated by the mass of the star.
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 from compacting due to the action of gravity, it burns the hydrogen and makes the outer layers of the star expand outward. Therefore, we first see that before being a white dwarf it is a red giant. Due to its large size, the heat expand as its surface temperature becomes colder. However, its core remains hot.
These stars are responsible for converting the helium in the nucleus into different heavier elements such as carbon. They then expel material from their outer layers and create a gas envelope. This gas envelope is considered a small atmosphere. The core continues to heat up and contracts to form the white dwarf.
Types and curiosities
Let's see what are the different types of white dwarf that exist:
- dA: they are white dwarfs that only have Balmer lines and have 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: possess 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 we see that they are excessively dense despite the fact that their radius is smaller than that of the sun. These bodies have the same solar density. During the cooling process of the stars, a gaseous material is released, 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.