The long-term study gave Hua Feng and them the illusion of returning to their student days, and that feeling that the world was still peaceful.

After the main sequence star core H is depleted, leaving the main sequence is the stage that begins its final journey. Outcomes depend primarily on quality. For stars with very small masses, the self-gravitational force inside the object is not important due to the small mass, and the equilibrium inside the solid is the net Coulomb gravitational force between positive and negative ions and the pressure between electrons to achieve equilibrium.

When the mass of the star is larger, until the gravitational force is not negligible, the self-gravitational force increases the internal density and pressure, and the increase in pressure is the ionization of the matter, so that the electrical confinement of the solid gradually disintegrates, and the transition to plasma gas. Increasing the mass, i.e. increasing the density, where the pressure is independent of temperature, thus achieving a "cold" equilibrium position, where the kinetic energy of the electrons in the plasma is large enough to cause β decay inside the substance:

Here p is the proton in the nucleus, such a reaction is roughly when the density reaches 1010g·cm-3, it will gradually change the nucleus in the negative ion into a neutron-rich nucleus, too many neutrons appear in the nucleus, resulting in a loose nuclear structure, when the density exceeds 4×1011g·cm-3 is the neutron begins to separate from the nucleus and becomes a free neutron, and the pressure between the neutrons reaches equilibrium due to gravity.

If the neutron gas pressure can no longer resist the gravitational pull of matter when the mass changes, and a black hole is formed, but because most of the post-evolution stages of the star make the mass less than its initial mass, such as stellar winds, "helium flashes", supernova explosions, etc., they will be a star that loses a large percentage of mass, therefore, the final outcome of the star is not judged by its initial mass, it actually depends on the evolutionary process.

Then we can draw such conclusions. A star below 8→10M⊙ eventually sheds some or most of its mass and becomes a white dwarf. Stars over 8M ⊙ will eventually become neutron stars or black holes through the gravitational collapse of the star's core, that is, stars with a collapsed core mass of 1.44 times the Sun to 5 times that of the Sun will eventually become neutron stars, and stars with a collapsed core mass of more than 5 times that of the Sun will eventually become black holes.

THE OBSERVED MASS RANGE OF STARS IS GENERALLY 0.1→60M⊙. A celestial body with a mass of less than 0.08 M⊙ cannot reach the ignition temperature. Therefore, without emitting light, it cannot be a star. THE TEMPERATURE OF THE CENTER OF THE CELESTIAL BODY WITH A MASS GREATER THAN 60 M⊙ IS TOO HIGH AND UNSTABLE, AND LESS THAN 70 HAVE BEEN FOUND SO FAR.

Based on actual observations and spectral analysis, we can understand the basic structure of a star's atmosphere. It is generally believed that in some stars, the outermost layer has a corona-like corona-like high-temperature and low-density corona.

It is often associated with the astral wind. Some stars have been found in the corona with a chromosphere that produces certain emission lines, and the inner atmosphere absorbs the continuous radiation of the higher temperature gases in the inner layer to form absorption lines. This layer of the atmosphere is sometimes referred to as the inverse layer, and the high-temperature layer of the emission continuum is called the photosphere. In fact, the process of forming stellar optical radiation shows that the photosphere is quite thick, and each layer of it is emitted and absorbed.

The photosphere cannot be separated from the inverter layer. Within the photosphere of a Sun-type star, there is a troposphere with an average radius of about one-tenth or more. In the interior of the upper and lower main sequence stars, the troposphere is positioned very differently. Energy transport is dominated by radiation in the photosphere and convection in the troposphere.

For photospheres and tropospheres, we often use models based on actual measured physical properties and chemical compositions for more detailed studies. Starting from the basic assumptions of hydrostatic equilibrium and thermodynamic equilibrium, we can establish a number of relationships to solve the pressure, temperature, density, opacity, productivity and chemical composition of different regions of the star. At the center of the star, the temperature can be as high as millions or even hundreds of millions of degrees, depending on the basic parameters and evolutionary stage of the star. There, different capacity reactions are carried out.

It is generally believed that stars are formed by the condensation of nebulae, and the stars before the main sequence cannot undergo thermonuclear reactions because they are not hot enough, and can only rely on gravitational contraction to produce energy.

After entering the main sequence, the temperature of the center reaches more than 7 million degrees, and the thermonuclear reaction of hydrogen fusion into helium begins. This process is long and is the longest phase in a star's life. After the hydrogen is burned, the star shrinks internally and expands externally, evolving into a large red giant with a low surface temperature and the potential for pulsation. Those stars whose internal temperature has risen to nearly 100 million degrees Celsius begin to undergo the helium-carbon cycle.

During these evolutionary processes, the temperature and luminosity of the star change according to certain rules, resulting in a certain track on the Herault diagram. Eventually, some stars explode as a supernova, their gas shells fly away, and their cores compress into compact stars like neutron stars and tend to "die".

Almost everything about a star depends on its initial mass, including essential characteristics such as luminosity and size, but also evolution, longevity, and eventual fate.

Most stars are between 1 billion and 10 billion years old, and some are even close to the observed age of the universe – 13.2 billion years old. The estimated age of the oldest star found so far is 13.4 billion years old.

The more massive a star is, the shorter its lifespan, mainly because the more massive the star's core, the higher the pressure and the faster the hydrogen is burned. Many supermassive stars have an average lifespan of only a million years, but the lightest stars (red dwarfs) burn their fuel at a very slow rate, and their lifespans can last from tens to trillions of years.

Due to their distance from the Earth, all stars except the Sun appear to the naked eye to be just a point of light in the night sky, and the light they enter the Earth is disturbed by the atmosphere, and the stars are "flashing" in the human eye. The Sun is also a star, but because it is so close to the Earth, it not only appears to be disk-shaped, but also provides daytime light. Aside from the Sun, the largest star appears to be R Swordfish, which has a diameter of 0.057 arc seconds.

Much of what we know about stars comes from theoretical models and simulations, which are based only on measurements of the spectrum and diameter of stars. In addition to the Sun, the first star to be measured in diameter was Betelgeuse, which was completed by Albert Abraham Michelson in 1921 using the 100-inch Hooke telescope at the Mount Wilson Observatory (about 1,150 Sun diameters).

For ground-based telescopes, the vast majority of stellar disks are too small to perceive their angular diameters, so interferometer telescopes are used to obtain images of these stars. Another technique for measuring the angular diameter of a star is occultation: this technique accurately measures the weakening of the moon's occultation (or the reappearance of the regression) of the moon, from which the apparent diameter of the star can be calculated.

Stars range in size from neutron stars measuring only 20 to 40 kilometers to supergiants like Betelgeuse in the constellation Orion, which are 1,150 times the diameter of the Sun, about 1.6 billion kilometers, but much less dense than the Sun. The largest star currently observed is VY Canis Major, which is about 10 billion times the size of the Sun and 50 times the mass of the Sun.

The motion of a star relative to the Sun can provide useful information about the age and origin of the star, and it also includes the structure and evolution of the surrounding galaxies. The components of a star's motion include radial velocity approaching or moving away from the Sun, and angular momentum across the sky, which is called self-movement.

Radial velocity is measured by the Doppler shift in the spectrum of a star and is measured in kilometers per second. The self-determination of a star is confirmed by precise astrometry in one millionth of an arc second (mas) per year. By measuring the parallax of the star, it can be converted to the actual unit of velocity. The higher the self-velocity, the closer the star is usually closer to the Sun, making highly self-contained stars ideal candidates for parallax measurements.

Once both motions have been measured, the spatial velocity of the star relative to the solar star system can be calculated. Among the neighboring stars, it has been found that the stellar velocity of the first group is generally lower than that of the older second group, which orbits in elliptical orbits inclined to the plane. Comparing the kinetic energy of neighboring stars can also derive and prove the structure of the constellation, which is like a group of stars that originate in the same huge molecular cloud and move together towards the same point.

The magnetic field of a star originates in the region where the circulation of convection inside the star begins to be generated. Plasma, which is electrically conductive, acts like a generator, causing a magnetic field that extends across the star. The strength of the magnetic field varies with the mass and composition of the star, and the total amount of magnetic activity on the surface depends on the rate at which the star rotates. Activity on the surface produces star spots, which are areas where the magnetic field on the surface is stronger than normal and the temperature is lower than normal. The arched coronal circle is a ring that enters the corona from a magnetically active area, and the star flame is a phenomenon in which high-energy particles erupt from the same magnetic field activity.

Young, high-speed rotating stars tend to have a high degree of surface activity due to the activity of the magnetic field. The magnetic field also strengthens the stellar wind, but the rate of rotation is like a floodgate, slowing down as the star ages. As a result, an older star like the Sun rotates at a lower rate and has a milder surface activity. The degree of activity of stars with slow rotation tends to change periodically and may temporarily cease to be active during the cycle. For example, in the case of the Mondstadt Minimum, the Sun was almost completely free of sunspot activity for about 70 years.

The rotation of a star can be roughly measured through a beamsplitter, or it can be measured with a traced spot. Young stars will have a high rotation speed that can exceed 100 km/s at the equator. For example, the equatorial velocity of the water commission of type B is as high as 225 km/s or more at the rotation, making the equatorial radius 50% larger than the extreme equator. Such a speed is only slightly lower than the critical speed of 300 km/s that would split the water commission. In comparison, the Sun rotates once in a 25–35-day cycle, and its rotation speed at the equator is only 1.994 km/s. The magnetic field of the star and the stellar wind slow down the rotation rate of the stars in the main sequence belt, which has an important influence on the evolution.

Degenerate stars compress into very dense matter, while causing high-speed rotation. But compared to their state at low rotational speeds, due to the conservation of angular momentum, a rotating object compensates for the loss in size by increasing the rate of rotation, and most of the dissipated angular momentum is carried away by the outward blowing of the stellar wind. In any case, the rotation of the wave is very fast, for example in the core of the Crab Nebula, which rotates at a rate of 30 revolutions per second. The rotation rate of the wave is slowed down by radiant emission.