All kinds of stars are needed, all kinds of stars are important… But aren't all the stars in the sky the same? Oddly enough, no. Star systems have different structures and different classifications of their components. And even the luminary in another system may not be one. It is on this basis that scientists first of all distinguish the star systems of the galaxy.
Before proceeding directly to the classification, it is worth clarifying what we are talking about in general. So, stellar systems are galactic units, consisting of stars rotating along an established path and gravitationally related to each other. In addition, there are planetary systems, which, in turn, consist of asteroids and planets. So, for example, an obvious example of a star system is the Solar System, familiar to us.
However, not the entire galaxy is filled with such systems. Star systems differ primarily in multiplicity. It is clear that this value is very limited, since a system with three or more equivalent stars cannot exist for a long time. Only hierarchy can guarantee stability. For example,so that the third stellar component does not end up "outside the gate", it should not approach the stable binary system closer than 8-10 radii. At the same time, it is not necessary that it be single - it may well be a double star. In general, for every 100 stars, about thirty are single, forty-seven are double, twenty-three are multiples.
Unlike constellations, multiple stars are interconnected by mutual gravity, while being located at a small distance from each other. They move together, rotating around the center of mass of their system - the so-called barycenter.
A striking example is Mizar, known to us from the constellation Ursa Major. It is worth paying attention to her "handle" - her middle star. Here you can see the dimmer glow of her pair. Mizar-Alcor is a double star, you can see it without special devices. If you use a telescope, it becomes clear that Mizar itself is a double, consisting of components A and B.
Star systems in which two luminaries are found are called binary. Such a system will be quite stable if there are no tidal effects, mass transfer by stars, and disturbances of other forces. At the same time, the luminaries move in an elliptical orbit almost indefinitely, rotating around the center of mass of their system.
Visual double stars
Those twin stars that can be seen through a telescope or even without devices are commonly called visual binaries. Alpha Centauri, toFor example, just such a system. The starry sky is rich in such examples. The third star of this system - the closest of all to our own - Proxima Centauri. Most often, such halves of a pair differ in color. So, Antares has a red and green star, Albireo - blue and orange, Beta Cygnus - yellow and green. All of these objects are easy to observe in a lens telescope, which allows specialists to confidently calculate the coordinates of the luminaries, their speed and direction of movement.
It often happens that one star of a star system is located too close to another. So much so that even the most powerful telescope is unable to capture their duality. In this case, a spectrometer comes to the rescue. When passing through the device, the light is decomposed into a spectrum delimited by black lines. These bands shift as the luminary approaches or moves away from the observer. When the spectrum of a binary star is decomposed, two types of lines are obtained, shifting as both components move around each other. Thus, Mizar A and B, Alcor are spectroscopic binaries. At the same time, they are also combined into a large system of six stars. Also, the visual binary components of Castor, a star in the constellation of Gemini, are spectroscopically binary.
Noticeable double stars
There are other star systems in the galaxy. For example, those whose components move in such a way that the plane of their orbits is close to the line of sight of an observer from the Earth. That means they obscure each othereach other, creating mutual eclipses. During each of them, we can observe only one of the luminaries, while their total brightness decreases. In the case when one of the stars is much larger, this decrease is noticeable.
One of the most famous noticeable double stars is Algol from the constellation Perseus. With a clear periodicity of 69 hours, its brightness drops to the third magnitude, but after 7 hours it again increases to the second. This star is often referred to as "The Winking Devil". It was discovered back in 1782 by the Englishman John Goodryk.
From our planet, a noticeable double star looks like a variable that changes brightness after a certain time interval, which coincides with the period of revolution of stars around each other. Such stars are also called noticeable-variables. In addition to them, there are physically variable luminaries - cypheids, the brightness of which is regulated by internal processes.
Evolution of binary stars
Most often, one of the stars of a binary system is a larger one, quickly passing through its life cycle. While the second star remains normal, its "half" turns into a red giant, then into a white dwarf. The most interesting thing in such a system begins when the second star turns into a red dwarf. White in this situation attracts the accumulated gases of the expanding "brother". About 100 thousand years is enough for the temperature and pressure to reach the level necessary for the fusion of nuclei. The gaseous shell of the star explodes with incredible force, causingthe luminosity of the dwarf increases by almost a million times. Earth observers call this the birth of a new star.
Astronomers also happen to discover such situations when one of the components is an ordinary star, and the second is very massive, but invisible, with a valid source of powerful X-rays. This suggests that the second component is a black hole - the remnants of a once massive star. Here, according to experts, the following happens: using the most powerful gravity, the black hole attracts the gases of the star. As they spiral in at great speed, they heat up, releasing energy in the form of X-rays before disappearing into the hole.
Scientists have concluded that a powerful X-ray source proves the existence of black holes.
Triple star systems
The solar star system, as you can see, has far from the only version of the structure. In addition to single and double stars, more of them can be observed in the system. The dynamics of such systems is much more complex than even that of a binary system. However, sometimes there are star systems with a small number of luminaries (however, exceeding two units), which have a rather simple dynamics. Such systems are called multiple. If there are three stars in the system, it is called triple.
The most common type of multiple systems is triple. So, back in 1999, in the catalog of multiple stars, out of 728 multiple systems, more than 550 are triple. According to the principle of hierarchythe composition of these systems is as follows: two stars are close, one is very distant.
In theory, the model of a multiple star system is much more complex than a binary one, since such a system can show chaotic behavior. Many such clusters turn out to be, in fact, very unstable, which leads to the ejection of one of the stars. Only those systems in which the stars are located according to a hierarchical principle manage to avoid such a scenario. In such cases, the components are divided into two groups, rotating around the center of mass in a large orbit. There should also be a clear hierarchy within groups.
Scientists know star systems with a large number of components. So, Scorpio has more than seven luminaries in its composition.
So, it turned out that not only the planets of the star system, but the systems themselves in the galaxy are not the same. Each of them is unique, different and extremely interesting. Scientists are discovering more and more stars, and we may soon learn about the existence of intelligent life not only on our own planet.