What is a White Dwarf?

White Dwarf (also known as degenerate dwarf) is a low luminosity, high density, high temperature star. Because it is white in color and relatively small in size, it is named a white dwarf. The surface temperature is 8000K, it emits white light, and has a life span of billions of years. ^[1]

White Dwarf (also known as degenerate dwarf) is a low

Low- and medium-mass stars pass through the main-sequence stage of their lifetime, ending with hydrogen fusion

Astronomy teaches us

Surface gravity

The surface gravity of a white dwarf of the same size as the Earth (such as Sirius B, Sirius' neighbor) is approximately 180,000 times the surface of the Earth. Under such high pressure

In order to use white dwarfs for cosmological chronology research, the cooling rate of white dwarfs must be calculated. The cooling rate of white dwarfs basically depends on two aspects ^[5]

White dwarfs belong to the stars that have evolved into old age,

The first white dwarf to be discovered was Pohe 40, a triple star. Its members are

Most of the hydrogen on the sun is gradually burning and turning into helium.

white dwarf

At the most stable main sequence star stage. For stars of the Sun's mass, the main sequence star stage lasts about 11 billion years. Stars are slowly contracting due to light emission, and during the contraction process, the density of the central part will increase, and the pressure will increase, so that hydrogen will burn more strongly, so that the temperature will rise and the sun's The brightness will gradually increase. Since the Sun entered the main sequence star stage 4.5 billion years ago, the brightness of sunlight has increased by 30%, and it is expected to continue to increase in the future, which will keep the temperature of the earth rising. When 6.5 billion years later, when the main sequence of the sun ends, it is expected that the brightness of the sun will be 2.2 times that of today, and the average temperature of the earth will be about 60 ° C higher than today. By then, even if there is still sea water on the earth, I am afraid it will soon be evaporated. If only from the average temperature, Mars would be the most suitable planet for human habitation. In the main sequence star phase, the inward force contracted by the star's own gravity and the outward force caused by the combustion will restrain each other to reach equilibrium. But after 6.5 billion years, the hydrogen in the central part of the sun will be burned out, and finally only the surrounding shell-shaped part will have hydrogen burning. In the area where the spherical shell no longer burns, it begins to shrink rapidly due to the weakening of the outward force that counteracts gravity. At this time, the sun will become more and more bright. This is another stage-the beginning of the red giant phase. The red giant phase will last for hundreds of millions of years, during which the sun will reach 2000 times the brightness, the temperature around Jupiter and Saturn will also rise, and Jupiter's ice satellites and rings that are characteristic of Saturn will be evaporated without trace. Eventually, the outer part of the sun will even expand to near Earth's orbit today.

On the other hand, gas will continue to be emitted from the outer part, and eventually the mass of the sun will be reduced to 60% of the main sequence star stage. As the gravity of the sun weakens, the planet begins to move away from the sun. When the mass of the sun is reduced to 60%, the distance between the planet and the sun is 70% larger than it is now. In this way, although Mercury and Venus are very likely to be engulfed, the Earth should survive a large distance before the outer part of the sun arrives, and Mars and Jupiter-type planets (Jupiter, Saturn, Uranus, Neptune) will also Survive.

A planet with a mass like the sun will only shrink to a certain degree in the central part of which the density has become very high, that is, the temperature will only rise to a certain degree, and the fire in the central part will gradually disappear. The sun gradually loses its light, and the expanded outer part will shrink and cool down into a dense white dwarf. The planets that have survived the test of the Red Giant era will continue to orbit the Sun, everything will be frozen, and the end of the silent state will be greeted by the solar system.

If a star like the sun turns into a white dwarf, it will rotate one revolution per second. Density is at least 1.41 × 10 ¹¹ kg / m ³