What is the mechanism by which stars above medium mass are burned to the point where their volume ex

The conclusion is credible, this state is called red giant.

Stars in their lifetimes are all gaseous, and their volume is related to their mass and temperature. In the case of a certain mass, the higher the temperature, the larger the volume. The temperature at this stage of the star is mainly determined by the material and intensity of the fusion.

The higher the molecular weight of nuclear fusion, the higher the temperature; The more massive the star, the more drastic the nuclear abruptness.

In the early and middle stages of the Sun's life, nuclear fusion is mainly hydrogen fusion into helium. Later in the Sun's life, when hydrogen fuel is exhausted (most of which has been converted to helium), the temperature drops and the volume decreases. As the volume decreases dramatically, the core temperature and pressure rise, reaching the requirements of helium fusion, igniting helium fusion.

At this time, the sun regains its energy, the temperature rises, and the volume increases.

Since the temperature of helium fusion is higher than that of hydrogen fusion, the volume of the sun will be much larger than the original volume of the sun, which is the red giant state. This process of shrinking and amplification repeats itself many times until all the fusion fuel is exhausted, and the sun of the red giant star will continue to shrink until it becomes the sun of a white dwarf.

Of course, in the process of shrinking, because the shrinkage is too drastic, a large ** will be produced, which will throw the outer layer of material into space, which is a nova explosion and a supernova explosion. If the final remaining mass after the explosion is still higher than the Chandrasekhar mass, the star becomes a black hole.

As for the fate of the earth, there is no need to wait for the sun to become a red giant, and even before that, due to the drop in the temperature of the sun, all life on the earth will be doomed long ago.

Gravitational attraction is always inward, and there are three types of forces that a star can use against gravity: molecular degenerate motion (normal stars), proton degenerate motion (white dwarfs), and neutron degenerate motion (neutron stars). The higher the temperature, the greater the degenerate motion, the stronger the ability to resist gravity, and the larger the volume.

And when the temperature drops to the point where all known degenerate motions are not enough to resist gravity, the star ends up as a black hole.

A medium-mass star like the Sun has a huge nucleus where 600 million tons of hydrogen turn into helium every second. A violent impact of huge amounts of nuclear energy towards the outside of the star can stop the gravitational contraction. However, the evolutionary process of "constant" will eventually come to an end, and when all the hydrogen has turned into helium, the fire in the core will not have enough fuel to sustain it, and the quiet days of the stars in the main sequence phase will come to an end, and the period of great turmoil will come.

As soon as the fuel runs out, the rate of the thermonuclear reaction is immediately drastically reduced, the equilibrium between gravity and radiation pressure is broken, and gravity takes over. Stars with helium nuclei and hydrogen shells begin to shrink under their own gravity, increasing pressure, density, and temperature, so that the unused hydrogen in the outer layer of the star begins to burn, and the result is that the outer shell begins to expand and the core contracts.

At temperatures of about 100 million degrees, the helium nuclei of the star's core fuse into carbon nuclei. Every third helium nucleus fuses into a carbon nucleus, which in turn captures the other helium nuclei to form an oxygen nucleus. The speed of these new reactions is quite different from that of slow hydrogen fusion.

They detonate as fast as lightning (helium shines), forcing the stars to adjust their structure as much as possible. After about a million years, the outflow of nuclear energy has stabilized. In the hundreds of millions of years that followed, the star was temporarily stable, the helium in the nuclear region was gradually depleted, and the combustion of hydrogen was pushed further and further into the outer layers.

However, there is a price to pay for the adjustment, when the star will expand to a large extent in order to adapt its structure to the increase in luminosity. It will be a billion times larger. During this process, the color of the star changes because its outer layer is far away from the hot core, and the temperature is lowered.

Stars in this state are called red giants.

In about 5 billion years, the Sun will become a red giant, and scientists have calculated that the Sun will become unusually large. However, the Sun's gravitational pull is also weakened by the decrease in mass, so Mars and all the outer planets will move outward. At this time, Mercury and Venus will be swallowed up by the Sun.

As for the fate of the Earth, if there were no tidal forces, the Earth's orbit would have fled to almost the astronomical unit. However, the study found that because the earth and the sun have tidal forces, the earth will still be swallowed by the sun's outer atmosphere.

The sun burns: it is not like a candle, it is not that the chemical reaction will end, it is not that the energy of light is gone, it is not the law of the immortality of matter; It is the conservation of energy, which is the magnetic field of the sun itself at an altitude of 20 billion kilometers, which makes the sun breathless, causing the sun to breathe at a frequency of visible light, and the magnetic field at an altitude of 20 billion kilometers is eternal, so the sun shines forever. As for the sun engulfing the earth, it is not because the sun is expanding in size, but because the sun is rotating more and more slowly, and one day it will stop, causing the centrifugal force to disappear and only gravity remains, when the sun will not only swallow the earth, but even Pluto, which is far away in the sky, will be swallowed up.

Nuclear fission, nuclear fusion.

To understand the burning of stars, we must first know the formation of stars. Stars are formed from cosmic gas (nebulae) and cosmic dust, and to be precise, a star is a gas planet at the beginning of its life. When the nebula and dust in a certain place reach a certain density, they are affected by the surrounding force field, especially the rotation of galaxies, and these gases begin to exhibit a rotation phenomenon.

It's like having a whirlpool in the water and then sucking everything around you into the whirlpool. The vortex of nebulae and dust relied on such a rotating gravitational attraction to slowly suck the surrounding nebulae and cosmic dust over, and the more they sucked in, the more they sucked in. Think about it, if the whirlpool is like a small house, if there is only one person in the house, you will feel very comfortable.

But if there are 10 of them, you will feel very crowded. But that's not the end of it. More and more gas is sucked in by the whirlpool, so a high pressure is generated, and this high pressure causes the molecules in the gas to collide directly, just like a crowded subway, crowded and sweaty when there are many people.

Under the action of such high pressure and high temperature, the atom begins to abandon the external electrons, and the neutrons in the atom do not have electrodes, so they are also discarded. It should be squeezed, and the proton begins to combine with other protons to form a heavier proton than the original, and the neutron also combines with other neutrons to form a heavier neutron. Then the heavier Zhizhi seeps protons and neutrons to form new atoms, and with the same amount of electrons as protons, new elements are born, and this process produces a lot of light and heat, which is nuclear fusion.

When a star begins to glow steadily, it stops absorbing nebulae from the outside world. Because of the force field balance, the gravitational pull (gravity) generated by the star's own elements can be balanced by the outward thrust produced by its own nuclear fusion. At this point, the star reaches a period of stability.

Over time, due to nuclear fusion, the heavier the elements in the mind become (from hydrogen to oxygen, and even the production of spine-spine heavy elements such as iron), and the heavier the elements, the less they can be fused (because the pressure and heat required to separate the atoms, protons and electrons of the heavy elements are higher), so nuclear fusion becomes weaker and weaker. On the other hand, because of the creation of heavy elements, the resulting gravitational pull (gravity) is increasing. As a result, the star is no longer able to maintain this gravitational equilibrium and begins to collapse into the inner space, until the star finally uses up its last bit of strength to throw the heavy elements away, which is called a superstar**.

Eventually, the star collapses into a white dwarf, a neutron star, a black hole, and a dead star.

A star will "condense" at a certain period of time, becoming a neutron star, it cannot be condensed forever.

Neutron stars are one of the few possible endpoints of a supernova at the end of a star's evolution through gravitational collapse. Elements such as hydrogen, helium, and carbon in the core of stars are depleted in nuclear fusion reactions, and when they are finally converted to iron, they cannot obtain energy from nuclear fusion. The outer material that has lost the support of the thermal radiation pressure will fall rapidly towards the core due to gravitational pull, which may cause the kinetic energy of the outer shell to be converted into heat energy and explode outward to produce a supernova**, or depending on the mass of the star, the inner region of the star will be compressed into a white dwarf, a neutron star or even a black hole.

To put it more specifically, neutron stars are dense objects left behind by stars. When a star is less than 10 times the mass of the Sun, it often ends up as a white dwarf.