Stars are huge balls of luminous plasma. There are a huge number of them within our galaxy. The stars have played an important role in the development of science. They were also noted in the myths of many peoples, served as navigation tools. When telescopes were invented, as well as the laws of motion of celestial bodies and gravity, scientists realized that all stars are similar to the Sun.
Definition
The main sequence stars include all those in which hydrogen turns into helium. Since this process is characteristic of most stars, most of the luminaries observed by man fall into this category. For example, the Sun also belongs to this group. Alpha Orionis, or, for example, the satellite of Sirius, do not belong to the main sequence stars.
Star groups
For the first time, scientists E. Hertzsprung and G. Russell took up the issue of comparing stars with their spectral types. They created a chart that displayed the spectrum and luminosity of stars. Subsequently, this diagram was named after them. Most of the luminaries located on it are called the celestial bodies of the mainsequences. This category includes stars ranging from blue supergiants to white dwarfs. The luminosity of the Sun in this diagram is taken as unity. The sequence includes stars of various masses. Scientists have identified the following categories of luminaries:
- Supergiants - I class luminosity.
- Giants - II class.
- Stars of the main sequence - V class.
- Subdwarfs - VI class.
- White dwarfs – class VII.
Processes inside the luminaries
From the point of view of the structure, the Sun can be divided into four conditional zones, within which various physical processes occur. The radiation energy of the star, as well as the internal thermal energy, arise deep inside the star, being transferred to the outer layers. The structure of the main sequence stars is similar to the structure of the luminary of the solar system. The central part of any luminary that belongs to this category on the Hertzsprung-Russell diagram is the core. Nuclear reactions are constantly taking place there, during which helium is converted into hydrogen. In order for hydrogen nuclei to collide with each other, their energy must be greater than the repulsion energy. Therefore, such reactions proceed only at very high temperatures. Inside the Sun, the temperature reaches 15 million degrees Celsius. As it moves away from the core of the star, it decreases. At the outer boundary of the core, the temperature is already half of the value in the central part. The density of the plasma also decreases.
Nuclear reactions
But not only in the internal structure of the main sequence stars are similar to the Sun. The luminaries of this category are also distinguished by the fact that nuclear reactions inside them occur through a three-stage process. Otherwise, it is called the proton-proton cycle. In the first phase, two protons collide with each other. As a result of this collision, new particles appear: deuterium, positron and neutrino. Next, the proton collides with a neutrino particle, and a nucleus of the helium-3 isotope is formed, as well as a quantum of gamma radiation. At the third stage of the process, two helium-3 nuclei fuse together, and ordinary hydrogen is formed.
In the process of these collisions during nuclear reactions, elementary particles of neutrinos are constantly produced. They overcome the lower layers of the star, and fly into interplanetary space. Neutrinos are also registered on the ground. The amount that is recorded by scientists with the help of instruments is incommensurably less than they should be according to the assumption of scientists. This problem is one of the biggest mysteries in solar physics.
Radiant zone
The next layer in the structure of the Sun and main sequence stars is the radiant zone. Its boundaries extend from the core to a thin layer located on the border of the convective zone - the tachocline. The radiant zone got its name from the way in which energy is transferred from the core to the outer layers of the star - radiation. photons,which are constantly produced in the nucleus, move in this zone, colliding with the plasma nuclei. It is known that the speed of these particles is equal to the speed of light. But despite this, it takes photons about a million years to reach the boundary of the convective and radiative zones. This delay is due to the constant collision of photons with the plasma nuclei and their re-emission.
Tachocline
The sun and main sequence stars also have a thin zone, apparently playing an important role in the formation of the magnetic field of the stars. It's called a tachocline. Scientists suggest that it is here that the processes of the magnetic dynamo take place. It lies in the fact that plasma flows stretch the magnetic field lines and increase the overall field strength. There are also suggestions that a sharp change in the chemical composition of the plasma occurs in the tachocline zone.
Convective zone
This area represents the outermost layer. Its lower boundary is located at a depth of 200 thousand km, and the upper one reaches the surface of the star. At the beginning of the convective zone, the temperature is still quite high, it reaches about 2 million degrees. However, this indicator is already insufficient for the process of ionization of carbon, nitrogen, and oxygen atoms to occur. This zone got its name because of the way in which there is a constant transfer of matter from the deep layers to the outer - convection, or mixing.
In a presentation aboutMain sequence stars can indicate the fact that the Sun is an ordinary star in our galaxy. Therefore, a number of questions - for example, about the sources of its energy, structure, and also the formation of the spectrum - are common both to the Sun and to other stars. Our luminary is unique in terms of its location - it is the closest star to our planet. Therefore, its surface is subjected to detailed study.
Photosphere
The visible shell of the Sun is called the photosphere. It is she who radiates almost all the energy that comes to Earth. The photosphere consists of granules, which are elongated clouds of hot gas. Here you can also observe small spots, which are called torches. Their temperature is approximately 200 oC higher than the surrounding mass, so they differ in brightness. Torches can exist for up to several weeks. This stability arises due to the fact that the magnetic field of the star does not allow the vertical streams of ionized gases to deviate in a horizontal direction.
Spots
Also, dark areas sometimes appear on the surface of the photosphere - the nuclei of spots. Often spots can grow to a diameter that exceeds the diameter of the Earth. Sunspots tend to appear in groups, then grow larger. Gradually, they break up into smaller areas until they disappear altogether. Spots appear on both sides of the solar equator. Every 11 years, their number, as well as the area occupied by spots, reach a maximum. According to the observed movement of the spots, Galileo was able todetect the rotation of the sun. Later, this rotation was refined using spectral analysis.
Until now, scientists are puzzled over why the period of increasing sunspots is exactly 11 years. Despite gaps in knowledge, information about sunspots and the periodicity of other aspects of the star's activity gives scientists the opportunity to make important predictions. By studying these data, it is possible to make predictions about the onset of magnetic storms, disturbances in the field of radio communications.
Differences from other categories
The luminosity of a star is the amount of energy that is emitted by the luminary in one unit of time. This value can be calculated from the amount of energy that reaches the surface of our planet, provided that the distance of the star from the Earth is known. The luminosity of main sequence stars is greater than that of cold, low-mass stars, and less than that of hot stars, which are between 60 and 100 solar masses.
Cold stars are in the lower right corner relative to most stars, and hot stars are in the upper left corner. At the same time, in most stars, unlike red giants and white dwarfs, the mass depends on the luminosity index. Each star spends most of its life on the main sequence. Scientists believe that more massive stars live much less than those that have a small mass. At first glance, it should be the opposite, because they have more hydrogen to burn, and they must use it longer. However, the starsmassive ones consume their fuel much faster.
