Shulou(Shulou.com)11/24 Report--

The luminescence of stars is produced by nuclear fusion, which turns light elements (such as hydrogen) into heavy elements (such as helium) and releases large amounts of energy. This energy radiates outward from the interior of the star in the form of light and heat, forming the stellar light we see.

However, stars do not always carry out nuclear fusion calmly. They also have to face a big problem, and that is gravity. Stars are compressed by huge clouds of gas, so they have a strong gravitational pull. This gravity causes the matter inside the star to collapse toward the center, making the star smaller and denser. If there is nothing to resist this gravity, the star will collapse until it becomes a black hole.

So, is there anything that can resist gravity? The answer is radiation pressure. The radiation pressure is caused by the force of photons on matter. You can imagine that when photons are emitted from the inside of the star, they crash into the material on the surface of the star, giving them an outward push. This thrust is like an air cushion that prevents matter from collapsing inward. When the radiation pressure and gravity reach equilibrium, the star can remain stable.

However, not all stars can achieve this balance. Some stars are too big and bright, and the radiation pressure they produce is so strong that it exceeds gravity. In this way, the material on the surface of the star will be blown away by radiation pressure, forming a strong stellar wind. In this case, the star can not remain stable, it will continue to lose mass and energy.

So, is there a limit that tells us how big and bright a star can be? The answer is Eddington limit. Eddington limit is a theoretically calculated value, which indicates the upper limit of luminosity when the radiation pressure of celestial bodies does not exceed gravity under the premise of spherical symmetry. In other words, if the luminosity of a celestial body exceeds the Eddington limit, it will be torn apart by its own radiation pressure.

What exactly is the Eddington limit? We can use a formula to express:. Where G is the universal gravitational constant, M is the mass of celestial bodies, MSPP is the mass of protons, c is the speed of light, and σ _ T is the Thomson scattering cross section of electrons. These are physical constants, and you don't have to worry too much about their specific values. You just need to know that this formula tells us that the Eddington limit is proportional to the mass of celestial bodies. In other words, the greater the mass of a celestial body, the greater the maximum luminosity it can emit.

So, can we use this formula to calculate the Eddington limit of the sun? The answer is yes. The mass of the sun is about 2 × 10 ^ 30kg. If you put it into the formula, we can get:

It represents the maximum luminosity emitted by solar energy, that is, 1.3 × 10 ^ 31 joules per second. In order to facilitate comparison, we can use the current luminosity of the sun as a reference. The sun's current luminosity is about 3.8 × 10 ^ 26 watts, which means that the sun now emits only about 1/1000 of the maximum energy it can emit. This shows that the sun is still stable and will not be blown away by its own radiation pressure.

So, are there any celestial bodies that exceed the Eddington limit? The answer is yes. If a star increases its brightness during a nuclear reaction and exceeds its Eddington limit, it will lose its balance and throw out a large amount of matter to form a stellar wind. This reduces the mass and brightness of the star, bringing it back to equilibrium, a phenomenon that can be observed in some variables.

In the actual observation, we can also see the stable existence of some supermassive stars. These stars can reach hundreds or even thousands of times the mass of the sun, so that the nuclear fusion energy they produce is so great that it exceeds the Eddington limit. There is no complete explanation for how such stars exist, and there may be some unknown factors that can break through the Eddington limit.

Scientists speculate that the possible reasons are: there are different levels of convective regions inside the star, which can transfer energy and matter and reduce radiation pressure; there is a strong magnetic field on the surface of the star, which can resist radiation pressure; there are companion stars around the star, which can provide extra gravity to stabilize the star. In short, stars beyond the Eddington limit are an interesting and complex problem in astronomy, which requires more observations and theories to explore.

This article comes from the official account of Wechat: Vientiane experience (ID:UR4351), author: Eugene Wang

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