All sorts of stars are needed, all sorts of stars are important ... But aren't all the stars in the sky the same? Oddly enough, no. Star systems have a different structure and different classification of their components. And even a star in another system may be more than one. It is on this basis that scientists primarily distinguish between stellar systems of the galaxy.
Before proceeding directly to the classification, it is worth clarifying what will be discussed at all. So, stellar systems are galactic units consisting of stars rotating along an established path and gravitationally interconnected. In addition, there are planetary systems, consisting, in turn, of asteroids and planets. So, for example, an obvious example of a stellar system is the Solar, familiar to us.
However, not the whole galaxy is filled with similar systems. Star systems differ primarily in multiplicity. It is clear that this quantity is very limited, since for a long time a system with three or more equivalent stars cannot exist. Sustainability can only be guaranteed by hierarchy. For example, so that the third stellar component does not appear “behind the gate”, it should not come closer to a stable binary system closer than 8-10 radii. Moreover, it is not necessary that he be single - it may well be a double star. In general, for 100 stars, about thirty are single, forty seven are double, twenty three are multiple.
Multiple stars
Unlike constellations, multiple stars are interconnected by mutual gravitation, being located, at the same time, 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 by the constellation Ursa Major. It is worth paying attention to her “pen” - her middle star. Here you can notice the dimmer radiance of her pair. Mitsar Alkor is a double star, you can see it without special devices. If you use a telescope, it will become clear that Mitsar itself is double, consisting of components A and B.
Double stars
Star systems in which two luminaries are found are called double. Such a system will be quite stable if there are no tidal effects, the transfer of mass by the stars, and disturbances of other forces. At the same time, the stars move in an elliptical orbit almost endlessly, revolving around the center of mass of their system.
Visual Double Stars
Those paired stars that can be seen through a telescope or even without devices are usually called visual doubles. Alpha Centauri, for example, is just such a system. The starry sky is rich in similar examples. The third luminary of this system is the closest of all to our own - Proxima Centauri. Most often, such halves of a pair vary in color. So, Antares has a red and green star, Albireo - blue and orange, Beta Swan - yellow and green. All of these objects are easy to observe with a lens telescope, which allows specialists to confidently calculate the coordinates of the stars, their speed and direction of movement.
Spectral Double Stars
It often happens that one star in the star system is too close to another. So much so that even the most powerful telescope is not able to catch their duality. In this case, the spectrometer comes to the rescue. When passing through the device, the light decomposes into a spectrum delimited by black lines. These bands shift as the star approaches or moves away from the observer. In the expansion of the spectrum of a binary star, two types of lines are obtained that shift as both components move around each other. So, Mizar A and B, Alcor - spectrally double. Moreover, they are also combined into a large system of six stars. Also, the visually binary components of Castor, the star in the constellation Gemini, are spectrally binary.
Visibly 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 the observer from the Earth. This means that they obscure each 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 noticeably binary stars is Algol from the constellation Perseus. With a clear periodicity of 69 hours, its brightness drops to the third value, but after 7 hours it again increases to the second. This star is often called the "Winking Devil." It was discovered back in 1782 by the Englishman John Goodrayk.
From our planet, a noticeably binary star looks like a variable that changes brightness after a certain time interval, which coincides with the period of stars circling around each other. Such stars are also called noticeably variable. In addition to them, there are physically variable luminaries - cipheids, the brightness of which is regulated by internal processes.
The evolution of double stars
Most often, one of the stars of the binary system is a larger one, quickly passing the life cycle allocated to it. 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 temperature and pressure to reach the level necessary for nuclear fusion. The gas shell of the luminary explodes with incredible strength, as a result of which the dwarf's luminosity increases almost a million times. Earth observers call this the birth of a new star.
Astronomers also happen to discover situations when one of the components is an ordinary star, and the second is very massive, but invisible, with an acceptable source of powerful x-ray radiation. 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 powerful gravity, a black hole attracts the gases of the star. Pulling in a spiral at a tremendous speed, they warm up, releasing energy in the form of x-rays before disappearing into the hole.
Scientists concluded that a powerful x-ray source proves the existence of black holes.
Triple Star Systems
The solar star system, as can be seen, is far from the only version of the structure. In addition to a single and double star, a larger number of them can be observed in the system. The dynamics of such systems is much more complicated than even a double one. However, sometimes there are stellar systems with a small number of luminaries (exceeding, however, two units), which have a fairly simple dynamics. Such systems are called multiple. If the stars included in the system are three, it has the name triple.
The most common type of multiple systems is triple. So, back in 1999, more than 550 are triple in the catalog of multiple stars from 728 multiple systems. Corresponding to the principle of hierarchy, the composition of these systems is as follows: two stars are closely spaced, one is far removed.
In theory, the model of a multiple stellar system is much more complex than a binary, since such a system can exhibit chaotic behavior. Many such clusters are, in fact, very unstable, which leads to the ejection of one of the stars. Such a scenario can only be avoided by those systems in which the stars are arranged according to a hierarchical principle. In such cases, the components are divided into two groups rotating around a center of mass in a large orbit. There should also be a clear hierarchy within groups.
Higher multiples
Scientists know stellar systems and with a large number of components. So, Scorpio has in its composition more than seven luminaries.
So, it turned out that not only the planets of the stellar system, but the systems themselves in the galaxy are not the same. Each of them is unique, different and extremely interesting. Scientists are discovering an increasing number of stars, and perhaps soon we will learn about the existence of intelligent life, not only on our own planet.