What is the source of star energy?

In order to understand this, we should consider the situation deep in the center of the star. Only one star allows us to study at close range, and that is the sun. The sun, like all ordinary stars, is a big white-hot gas ball, which can swallow 654.38+0 billion earths. Its surface temperature is 5600℃, and where the core generates energy, the temperature is as high as150,000℃. We can't see the deeper part of the sun, but we can detect its composition. The mathematical model established by us can be consistent with the observation results, so we are convinced of the prediction of the core temperature. 70% of the mass of the sun is hydrogen, and hydrogen is also its fuel, just like the original stars.

We know that hydrogen is the simplest atom, consisting of a proton and a surrounding electron. The interior of the star is too hot, and electrons are stripped from the edge of the nucleus, leaving incomplete atoms, which is called "ionization". In the core of a star, the pressure and temperature are extremely high, and the speed of these nuclei is so great that nuclear reactions will occur when they collide with each other. Hydrogen nuclei combine to form the second lightest element, namely helium nuclei. It is recognized that this process is indirect and tortuous, and the final effect is that four hydrogen nuclei are combined into 1 helium nucleus. This process not only produces the light from the stars we see, but also produces another by-product called neutrinos, which will be discussed later. In the process of forming helium, a little mass is lost and a lot of energy is released. It is these released energies that make the stars shine. For the sun, it loses 4 million tons of mass every second. The mass of the sun is much smaller now than when you first read this article. Hydrogen fuel cannot be supplied forever, but there is no danger at present. The sun was born about 5 billion years ago. According to the standard of stars, it is in its heyday. When all the hydrogen is exhausted, the sun does not simply darken, but another story will happen, which will be told in later chapters.

So at least in the sun, energy comes from the mass lost when four hydrogen nuclei combine to form 1 lighter helium nuclei. The most famous formula e = mc2 in nature tells us that mass (m) is equivalent to energy (e), and the conversion coefficient c2 is the square of the speed of light, which is very large. So a little mass consumption will produce huge energy, and the sun will lose 4 million tons of matter every second and convert it into energy!

Where did these lost people come from? Hydrogen atom is the simplest atom, and there are only 1 electrons around 1 proton. So each of the four hydrogen nuclei is 1 proton; Helium nucleus consists of two protons and two neutrons. But neutrons are slightly heavier than protons, so if you add up the masses of these particles directly, you will find that 1 helium nucleus is heavier than 4 hydrogen nuclei, but the mass has increased! But in fact, although the helium nucleus is composed of heavier particles, its total mass is indeed less than 4 protons. Remember that this field is dominated by quantum mechanics and its related effects, and the answer is here. If we measure the mass of a single proton, it is indeed lighter than a neutron. But these subatomic particles are not free. In helium nuclei, they are bound together by strong nuclear forces and cannot move freely. When subatomic particles form this bond, they will release energy, and the result we measured is a decrease in mass.

Why does the nucleus produced have two protons and two neutrons? If two independent protons can form a stable binding relationship, then the study of nuclear reactions by astrophysicists will become much simpler. Because in that case, two protons can combine into this "light helium nucleus" and release electromagnetic waves. But the two protons have the same positive charge, and the electromagnetic force repels each other, but the force between them is not enough to bind them together. Therefore, unlike this simple proton combination, in the sun and other stars, this process is quite complicated and surprisingly slow.

Because it is impossible to simply combine two protons together, we must bypass this obstacle and form a more complex nuclear state. In the following discussion, only the nucleus needs to be considered, not the whole atom. Because at such a high temperature inside a star, the electrons surrounding the nucleus and forming atoms are already too high to be captured. The only thing that works is the weak nuclear force, which will make protons spontaneously decay into neutrons, releasing 1 positrons and 1 neutrinos. Newly generated neutrons can be captured by passing protons to form deuterium. Deuterium is actually heavy hydrogen, equal to 1 neutron and 1 proton. Weak strength is worthy of the name, and this step will take a long time. At the center of the sun, a proton may wait an average of 5 billion years to form a deuterium, and then everything is much faster.

In an average time of about 1 sec, deuterium will capture another proton and combine with two protons and 1 neutron to form a stable nucleus, namely helium -3, a lighter form of helium. About 500,000 years later, this nucleus will collide with another to form a helium nucleus with two protons and two neutrons that we are more familiar with, and release two protons at the same time to participate in the next cycle. Combining two positively charged nuclei is a difficult and slow step. A strong force acting only at a very close distance attracts two nuclei together, while an electromagnetic force resists the strong force and keeps them away from each other. Finally, the nuclei will be close enough for the force to work. In this way, we finally get energy in the form of radiation, a positron-it will combine with its antiparticle to release energy-and a neutrino.

Neutrinos are tiny particles that move at high speed and hardly interact with other particles. Therefore, after it is emitted from the center of the sun, it is relatively unimpeded by the surrounding gas. Some of them will reach the earth and be discovered by the large detectors we built. For many years, there has been such a problem, that is, we expect that every collision that produces helium nuclei will produce a neutrino, and too few neutrinos are detected. However, neutrinos have an amazing ability to change their "tastes" or types on the way. Particle physicists have found that there are three kinds of neutrinos, which can be transformed into each other over time. The initial experiment was only sensitive to a specific type of neutrino, but could not detect other types of neutrinos. In a word, these experiments tell us that our understanding of the central reaction of the sun is far higher than any experiment conducted on earth, and it is basically correct. These experiments also provide reliable evidence for the first time that neutrinos have limited (though small) mass. Because if they don't have the mass previously thought, it is impossible to change from one particle type to another.