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Black Dwarf: black dwarf star exist in the universe

Black Dwarf
Black Dwarf

Black Dwarf: In the universe

Black Dwarf: There is a type of celestial body in astrophysics. We call it a black dwarf. It is the last stage of low-mass star evolution. And can really be called a "corpse" of stars. It does not emit any electromagnetic radiation and is composed of low-temperature electron degenerate matter and gas, which is difficult to distinguish from the planet in appearance.

we have found stars of various spectral types, including various intermediate and terminal forms during the evolution of stars, including white dwarfs, neutron stars, and black holes. So is there a terminal star corpse like a black dwarf in the universe today? How long does it take for a solar-like star, or a star with a lower mass than the sun, to run out of nuclear fuel to cool down and form a black dwarf? To understand this problem, we need to fully explore the evolution of the star from its birth.

Black Dwarf: Neutron stars were born from black dwarfs

We know that the cosmic interstellar space is filled with a large number of gas clouds. These gas clouds are not evenly distributed in density. There are some areas that are not only higher in density than the average density, but also maybe the areas with the highest density in gas clouds, and some areas. The density may be lower, or even lower than the average density of the entire gas cloud.

Under the influence of gravity, the gas cloud will begin to collapse at different points due to the uneven distribution of matter. High-density regions will attract more and more materials, slightly lower-density regions will absorb a small number of substances, and those with lower-density regions will be transferred to these high-density regions. This is a process of snatching material.

Black Dwarf: Gravitation is an out-of-control process,

which means that the more matter there is, the greater the gravitational force, and the faster it can attract surrounding matter. The size of a cloud of gas generally ranges from hundreds of thousands to millions of light-years. It may take millions or even tens of millions of years for a gas cloud to change from a large diffuse state to a relatively tightly collapsed state. But as long as the above process is completed, from the collapsed gas cloud state to the birth of a star cluster, which is the collapse point of the gas cloud, it takes only hundreds of thousands of years to ignite nuclear fusion.
You see, all the glowing points in the picture above are those that had a relatively high density of matter. They won in the process of robbing matter, so stars of various sizes and colors were born.

Black Dwarf: In a star cluster,

The most visible stars are the stars with the highest mass, the brightest luminosity, the bluest color, and the highest temperature. Their masses generally range from tens to hundreds of times the mass of the sun, while the luminosity is the sun. Countless thousands to millions of times. However, these stars are generally rare, accounting for less than 1% of the total number of stars in the universe, and they burn fuel fast in their cores and have a fierce nuclear reaction. The shortest life is only tens of thousands of years, and the longest is several Million years.

When such stars run out of core fuel. The nuclear reaction ends abruptly and then dies in a spectacular Type II supernova explosion. This is because after the core stops fusion. It will rapidly collapse under the action of gravity and release huge gravitational potential energy. While the low-mass core will collapse into a neutron star, and the higher-mass core will collapse all the way Blackhole. At the same time, the release of gravitational potential energy will blast all the material in the outer layer into the interstellar medium and form all the heavy elements known so far.

These element-rich gas clouds will bond to many organic molecules in the long years. Providing conditions for the birth of the next generation of stars, rocky planets, and even life.

The black hole formed is completely black if there is no companion or rich interstellar medium around it. And it will only emit low-temperature Hawking radiation. If there is matter around, a disc of matter with high-energy radiation (X-rays), or even a jet of matter in the center, will form around the black hole. In general, a black hole is the final corpse of a star and is completely invisible in black. But neutron stars are different.

Neutron stars have undergone rapid

Neutron stars have undergone rapid and violent compression during the process of formation. We compact any object in our life to make it warm, of course, the same is true of neutron stars. In minutes or even less, the cores that were once rich in iron, nickel, cobalt, silicon, and sulfur that were about several hundred thousand kilometers in diameter were quickly compressed by gravity into spheres with a diameter of 16 kilometers or even smaller, with a density Increased to 40 million times before, the core layer reached a high temperature of about 10 ^ 12 K, and the surface reached a maximum of about 10 ^ 6K.

Huge energy is stored in such a very small volume and the temperature is very high. Neutron stars not only emit blue and white light in the visible spectrum but also release a large amount of invisible high-energy radiation. Such as X-rays. But if the huge amount of energy can't radiate effectively. It can only radiate energy through the very small surface area of the neutron star. So this process is very slow.

So how long does it take for the neutron star to cool?

This process is divided into neutrino cooling and photon cooling. Because neutrinos are also a kind of radiation particles, and neutrinos usually do not interact with matter. That is, they will quickly escape from the neutron star after generation. So the neutron star ’s Neutrino cooling takes only 10 ^ 16 years,

which is one million times the age of the universe today. However, it is not so easy for photons to escape from the interior of the neutron star. It will collide with various charged particles and be scattered randomly in all directions. Therefore, it may take 10 ^ 20 to 10 ^ to cool the neutron star at the spectral end. 22 years is a particularly long process. This also means that there are no black dwarfs formed after the neutron star cools down in the universe today.
In addition to neutron stars, there are relatively low-density objects that cool faster.

The birth of white dwarfs and black dwarfs

As mentioned above, most stars in the universe are less massive than these blue and bright stars. When they die, supernova explosions do not occur, but their cores shrink slowly and relatively gently into a white dwarf. The birth of a white dwarf usually takes tens of thousands of years. And it does not collapse in a short time.

There are also white dwarfs that are much larger than neutron stars. And are generally about the same size as the Earth. This means that although the temperature of white dwarfs exceeds 20,000 K and is more than three times higher than the sun. It cools down much faster than neutron stars.

The cooling of white dwarfs also relies on the surface radiating energy into space. If you want a white dwarf to cool to a few degrees above absolute zero, the time scale is about 10 ^ 14 to 10 ^ 15 years.

In other words, after about 10 trillion years, or about 1,000 times the current age of the universe, the temperature of a "white dwarf" will drop, leaving the visible range. At that time, the universe will have a brand new celestial body: the black dwarf.

So, to sum up, there are no black dwarfs in the universe today, because our universe is too young. Scientists estimate that since the first white dwarf with the lowest energy in the universe. Less than 0.2% of its total heat has been lost. This tells us that if we want to find a real black dwarf. We need to go through a long time scale.

At present, our universe is full of all kinds of stars. They are far apart and form different galaxy structures. But when we waited for the first black dwarf to appear. Our local galaxy group had already merged into a large one. The elliptical galaxy, most of the stars, of course, including the sun, have already been exhausted and died. The remaining stars in the universe are only the lowest mass red dwarfs, and those failing stars: brown dwarfs.


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