Stars are huge balls made up of luminous plasma. Within our galaxy, there are a huge number of them. Stars played an important role in the development of science. They were also noted in the myths of many nations, served as navigation tools. When telescopes were invented, and the laws of motion of celestial bodies and gravity were discovered, scientists realized that all stars are like the sun.
Definition
The main sequence stars include all those inside which hydrogen is converted to helium. Since this process is characteristic of most stars, this category includes the majority of luminaries observed by man. For example, the Sun also belongs to this group. Alpha Orion, or, for example, Sirius’s satellite does not belong to the main sequence stars.
Star groups
For the first time, scientists E. Herzshprung and G. Russell took up the issue of comparing stars with their spectral classes. They created a diagram that displayed the spectrum and luminosity of stars. Subsequently, this chart was named after them. Most of the luminaries located on it are called the celestial bodies of the main sequence. 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 of luminosity.
- Giants - Grade II.
- The stars of the main sequence are V class.
- Sub-dwarfs - VI class.
- White dwarfs - VII class.
Processes within the luminaries
In terms of 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 luminary, being transmitted to the outer layers. The structure of the main sequence stars is similar to the structure 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 constantly occur there, during which helium turns into hydrogen. In order for hydrogen nuclei to collide with each other, their energy must be higher than the repulsion energy. Therefore, such reactions occur only at very high temperatures. Inside the sun, temperatures reach 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 the value in the central part. Plasma density 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 the 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. Then a proton collides with a neutrino particle, and a nucleus of the helium-3 isotope appears, as well as a gamma-ray quantum. At the third stage of the process, two helium-3 nuclei merge with each other, and the formation of ordinary hydrogen occurs.
During these collisions during nuclear reactions, elementary neutrino particles are constantly produced. They overcome the lower layers of the sun, and fly into interplanetary space. Neutrinos are also recorded on the ground. The amount recorded by scientists using instruments is incommensurably less than what they should be, according to scientists. This problem is one of the biggest mysteries in the physics of the sun.
Radiant zone
The next layer in the structure of the Sun and the stars of the main sequence is the radiant zone. Its boundaries extend from the core to a thin layer located on the boundary of the convective zone - tachocline. The radiant zone got its name from the method by which energy is transferred from the core to the outer layers of the star - radiation. Photons that are constantly produced in the nucleus move in this zone, colliding with plasma nuclei. It is known that the speed of these particles is equal to the speed of light. But despite this, photons need about a million years to reach the boundary of the convective and radiant zones. Such a delay occurs due to the constant collision of photons with plasma nuclei and their reradiation.
Tachocline
The sun and stars of the main sequence also have a thin zone, apparently playing an important role in the formation of the magnetic field of the stars. It is called tachocline. Scientists suggest that it is here that the processes of the magnetic dynamo occur. It consists in the fact that plasma flows stretch magnetic field lines and increase the total field strength. There are also suggestions that in the tachocline zone there is a sharp change in the chemical composition of the plasma.
Convection zone
This area is the outermost layer. Its lower boundary is located at a depth of 200 thousand km., And the upper reaches the surface of the body. At the beginning of the convection zone, the temperature is still quite high, it reaches about 2 million degrees. However, this indicator is already insufficient for the ionization of carbon, nitrogen, and oxygen atoms to occur. This zone got its name because of the method by which there is a constant transfer of matter from the deep layers to the outer ones - convection, or mixing.
In the presentation about the stars of the main sequence, you 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 for the Sun and for other stars. Our star is unique in its location - it is the star closest to our planet. Therefore, its surface is subjected to detailed study.
Photosphere
The visible shell of the Sun is called the photosphere. It is it that radiates almost all the energy that comes to Earth. The photosphere consists of granules, which are oblong clouds of hot gas. Here you can also observe small specks called torches. Their temperature is approximately 200 ° C higher than the surrounding mass, so they differ in brightness. Torches can last up to several weeks. This stability is due to the fact that the magnetic field of the star does not allow vertical flows of ionized gases to deviate in the horizontal direction.
Stains
Also on the surface of the photosphere dark areas sometimes appear - seed spots. Often spots can grow to a diameter that exceeds the diameter of the Earth. Sunspots, as a rule, appear in groups, then grow. Gradually they are crushed 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 the spots, reaches a maximum. By the observed movement of the spots, Galileo was able to detect the rotation of the Sun. This rotation was further refined using spectral analysis.
Until now, scientists are puzzling over why the period of increasing sunspots is exactly 11 years. Despite gaps in knowledge, information about sunspots and the frequency of other aspects of the star’s activities give scientists the opportunity to make important predictions. By studying these data, you can 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 star in one unit of time. This value can be calculated by the amount of energy that reaches the surface of our planet, provided that the distance of the star to the Earth is known. The luminosity of the main sequence stars is greater than that of cold stars with a small mass, and fewer hot stars, whose mass is from 60 to 100 solar stars.
Cold stars are in the lower right corner relative to most luminaries, while hot stars are in the upper left corner. Moreover, in most stars, unlike red giants and white dwarfs, the mass depends on the luminosity index. Each star spends most of her 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 other way around, because they have more hydrogen for combustion, and they should spend it longer. However, massive stars use their fuel much faster.