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First, let's find out which stars are called this. Physically, double stars rotate in ellipses around a common center of mass. However, if you measure the coordinates of one star relative to another, it turns out that the stars move relative to each other also in ellipses. In this figure, we took the more massive blue star as our origin. In such a system, the center of mass (green dot) describes an ellipse around the blue star.
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visual binaries astrometric binaries eclipsing binaries spectrally binaries
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Often stars in pairs differ greatly in brightness; the dim star is overshadowed by the bright one. Sometimes in such cases, astronomers learn about the duality of a star by deviations in the movement of a bright star under the influence of an invisible satellite from the trajectory in space calculated for a single star. Such pairs are called astrometric binaries. In particular, Sirius was classified as this type of binary for a long time, until the power of telescopes made it possible to discern a hitherto invisible satellite - Sirius B. This pair became visually double.
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It happens that the plane of revolution of stars around their common center of mass passes or almost passes through the eye of the observer. The orbits of the stars of such a system are located, as it were, edge-on to us. Here the stars will periodically eclipse each other, the brightness of the entire pair will change with the same period. This type of binary is called an eclipsing binary. If we talk about the variability of a star, then such a star is called an eclipsing variable, which also indicates its duality. The very first discovered and most famous binary of this type is the star Algol (Eye of the Devil) in the constellation Perseus.
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The last type of binary is the spectroscopic binary. Their duality is determined by studying the spectrum of the star, in which periodic shifts of absorption lines are noticed or it is clear that the lines are double, on which the conclusion about the duality of the star is based.
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Often, however, there are so-called multiple systems, with three or more components. However, the motion of three or more interacting bodies is unstable. In a system of, say, three stars, one can always distinguish a double subsystem and a third star revolving around this pair. In a four-star system, there may be two binary subsystems orbiting a common center of mass.
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Firstly, they make it possible to find out the masses of stars, since it is easiest and most reliable to calculate from the visible interaction of two bodies. Direct observations make it possible to find out the total “weight” of the system, and if we add to them the known relationships between the masses of stars and their luminosities, which were discussed above in the story about the fate of stars, then we can find out the masses of the components and test the theory. Single stars do not provide us with such an opportunity. In addition, as was also mentioned earlier, the fate of stars in such systems can be strikingly different from the fate of the same single stars.
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Types of double stars First, let's find out which stars are called so. Let's immediately discard the type of double stars that are called "optical double stars." These are pairs of stars that happen to be nearby in the sky, that is, in the same direction, but in space, in fact, they are separated by large distances. We will not consider this type of double. We will be interested in the class of physically binary stars, that is, stars truly bound by gravitational interaction.
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Position of the center of mass Physically, double stars rotate in ellipses around a common center of mass. However, if you measure the coordinates of one star relative to another, it turns out that the stars move relative to each other also in ellipses. In this figure, we took the more massive blue star as our origin. In such a system, the center of mass (green dot) describes an ellipse around the blue star. I would like to warn the reader against the common misconception that it is often believed that a more massive star attracts a low-mass star more strongly than vice versa. Any two objects attract each other equally. But an object with a large mass is more difficult to move. And although a stone falling on the Earth attracts the Earth with the same force as its Earth, it is impossible to disturb our planet with this force, and we see how the stone moves.
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Often, however, there are so-called multiple systems, with three or more components. However, the motion of three or more interacting bodies is unstable. In a system of, say, three stars, one can always distinguish a double subsystem and a third star revolving around this pair. In a four-star system, there may be two binary subsystems orbiting a common center of mass. In other words, in nature, stable multiple systems always reduce to systems of two terms. The system of three stars includes the well-known Alpha Centauri, considered by many to be the closest star to us, but in fact, the third weak component of this system - Proxima Centauri, a red dwarf - is closer. All three stars of the system are visible separately due to their proximity. Indeed, sometimes the fact that a star is double is visible through a telescope. Such doubles are called visual doubles (not to be confused with optical doubles!). As a rule, these are not close pairs; the distances between the stars in them are large, much larger than their own sizes.
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The brilliance of double stars Often the stars in pairs differ greatly in brightness; the dim star is overshadowed by the bright one. Sometimes in such cases, astronomers learn about the duality of a star by deviations in the movement of a bright star under the influence of an invisible satellite from the trajectory in space calculated for a single star. Such pairs are called astrometric binaries. In particular, Sirius was classified as this type of binary for a long time, until the power of telescopes made it possible to discern a hitherto invisible satellite - Sirius B. This pair became visually double. It happens that the plane of revolution of stars around their common center of mass passes or almost passes through the eye of the observer. The orbits of the stars of such a system are located, as it were, edge-on to us. Here the stars will periodically eclipse each other, the brightness of the entire pair will change with the same period. This type of binary is called an eclipsing binary. If we talk about the variability of a star, then such a star is called an eclipsing variable, which also indicates its duality. The very first discovered and most famous binary of this type is the star Algol (Eye of the Devil) in the constellation Perseus.
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Spectrally binary stars The last type of binary is the spectrally binary. Their duality is determined by studying the spectrum of the star, in which periodic shifts of absorption lines are noticed or it is clear that the lines are double, on which the conclusion about the duality of the star is based.
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Why are double stars interesting? Firstly, they make it possible to find out the masses of stars, since it is easiest and most reliable to calculate from the visible interaction of two bodies. Direct observations make it possible to find out the total “weight” of the system, and if we add to them the known relationships between the masses of stars and their luminosities, which were discussed above in the story about the fate of stars, then we can find out the masses of the components and test the theory. Single stars do not provide us with such an opportunity. In addition, as was also mentioned earlier, the fate of stars in such systems can be strikingly different from the fate of the same single stars. Celestial pairs, the distances between which are large compared to the size of the stars themselves, at all stages of their lives live according to the same laws as single stars, without interfering with each other. In this sense, their duality does not manifest itself in any way.
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Close pairs: the first exchange of masses Binary stars are born together from the same gas and dust nebula; they have the same age, but often have different masses. We already know that more massive stars live “faster”, therefore, a more massive star will overtake its peer in the process of evolution. It will expand, turning into a giant. In this case, the size of the star can become such that matter from one star (inflated) begins to flow to another. As a consequence, the mass of the initially lighter star can become greater than the initially heavy one! In addition, we will get two stars of the same age, and the more massive star is still on the main sequence, that is, in its center the synthesis of helium from hydrogen is still ongoing, and the lighter star has already used up its hydrogen, and a helium core has formed in it. Let us remember that in the world of single stars this cannot happen. Due to the discrepancy between the age of the star and its mass, this phenomenon is called the Algol paradox, in honor of the same eclipsing binary. The star Beta Lyrae is another pair that is exchanging mass right now.
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The matter from the inflated star, flowing onto the less massive component, does not immediately fall on it (the mutual rotation of the stars prevents this), but first forms a rotating disk of matter around the smaller star. The frictional forces in this disk will reduce the speed of the particles of matter, and it will settle on the surface of the star. This process is called accretion, and the resulting disk is called accretion. As a result, the initially more massive star has an unusual chemical composition: all the hydrogen in its outer layers flows to another star, leaving only a helium core with admixtures of heavier elements. Such a star, called a helium star, quickly evolves to form a white dwarf or a relativistic star, depending on its mass. At the same time, an important change occurred in the binary system as a whole: the initially more massive star gave up this superiority.
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Second mass exchange In binary systems, there are also X-ray pulsars emitting in a higher energy wavelength range. This radiation is associated with the accretion of matter near the magnetic poles of a relativistic star. The source of accretion is stellar wind particles emitted by the second star (the solar wind has the same nature). If the star is large, the stellar wind reaches a significant density, and the energy of the X-ray pulsar radiation can reach hundreds and thousands of solar luminosities. An X-ray pulsar is the only way to indirectly detect a black hole, which, as we remember, cannot be seen. And a neutron star is a rare object for visual observation. This is far from all. The second star will also sooner or later inflate, and matter will begin to flow to its neighbor. And this is already the second exchange of matter in a binary system. Having reached large sizes, the second star begins to “return” what was taken during the first exchange.
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If a white dwarf appears in the place of the first star, then as a result of the second exchange, flares can occur on its surface, which we observe as new stars. At one point, when there is too much material falling onto the surface of a very hot white dwarf, the temperature of the gas near the surface rises sharply. This provokes an explosive burst of nuclear reactions. The star's luminosity increases significantly. Such outbreaks can be repeated, and they are called repeated new ones. Repeated flares are weaker than the first, as a result of which the star can increase its brightness tens of times, which we observe from Earth as the appearance of a “new” star.
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Another outcome in a white dwarf system is a supernova explosion. The consequence of the flow of matter from the second star may be that the white dwarf reaches a maximum mass of 1.4 solar. If it is already an iron white dwarf, then it will not be able to maintain gravitational compression and will explode. Supernova explosions in binary systems are very similar in brightness and development to each other, since stars always explode with the same mass - 1.4 solar. Let us recall that in single stars the central iron core reaches this critical mass, and the outer layers can have different masses. In binary systems, as is clear from our narrative, these layers are almost absent. That is why such flares have the same luminosity. By noticing them in distant galaxies, we can calculate distances much greater than can be determined using stellar parallax or Cepheids. The loss of a significant portion of the mass of the entire system as a result of a supernova explosion can lead to the disintegration of a binary. The force of gravitational attraction between the components is greatly reduced, and they can fly apart due to the inertia of their movement.
"Neutron star" - 7. 8. Measured masses of neutron stars. Stars with higher central density and higher mass turn out to be unstable. Internal structure of neutron stars. 2. Direct introduction of many-particle forces in isovector channels: Relativistic mean field (RMF) model. Introduction of many-particle forces.
“Binary stars” - Visually double, astrometrically double, eclipsingly double, spectrally double. First, let's find out which stars are called this. Why are double stars interesting? Single stars do not provide us with such an opportunity. The last type of binary is the spectroscopic binary. Spectrally double. Eclipsing doubles.
“Mass of stars” - Mass almost equal to the Sun, and 2.5 times larger than the Earth. Source of energy from the Sun and stars. Main sequence. The densities of main sequence stars are comparable to the solar density. The masses of stars range from approximately 1/20 to 100 times the mass of the Sun. Betelgeuse is a red supergiant.
"Constellations" - There are also stars of the seventh, eighth and even eighteenth magnitude. A first magnitude star is exactly 2.512 times brighter than a second magnitude star. On a cloudless and moonless night, far from populated areas, about 3,000 stars can be distinguished. The winter triangle is made up of the brightest stars Orion, Canis Major and Canis Minor.
"Constellation Astronomy" - Based primarily on observations. But not only Akid fell in love with Galatea. Spiral galaxy M74. The names of the constellations were associated with myths, names of gods, names of instruments and mechanisms. Let's start getting acquainted with the constellations in the summer sky. Ursa Minor. Zodiacs. In the north hangs the inverted dipper of the Big Dipper.
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As observations have shown, many of them form pairs or are members of complex systems. Moreover, in our Galaxy alone, approximately half of all stars belong to binary systems. Binary stars are closely spaced pairs of stars.
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Origin and evolution of binary stars Like single stars, binary systems are formed under the influence of gravitational forces from a cloud of gas and dust. In modern astronomy, there are three most popular theories for the formation of double stars. The first of them connects the formation of binary systems with the separation at an early stage of the common core of the protocloud, which served as the material for the emergence of the binary system. The second theory is associated with the fragmentation of the protostellar disk, as a result of which not only binary, but also multiple star systems can appear. Fragmentation of the protostellar disk occurs at a later stage than the fragmentation of the core. The latest theory states that the formation of double stars is possible through dynamic physical and chemical processes inside the protocloud, which serves as material for star formation
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Scientists say that double stars make up about half of all the stars in our galaxy. A double star is a system consisting of two objects (stars) connected by gravitational forces. Both stars in the system rotate around their common center of mass. The distances between stars may differ, as well as the mass of these stars, as well as their sizes. Both stars included in the gravitational system can have both similar and distinctive characteristics. For example, star A may have a greater mass or size than star B.+ Double stars are traditionally labeled with Latin letters. Usually the letter “A” is marked with a brighter and more massive companion. The letter “B” is a less luminous and massive star. A striking example of a double star system is the closest star system to us - Alpha Centauri A and B. It is an integral system of two stars. Alpha Centauri itself consists of three components. If you look at this star without using various optical instruments, to the naked eye it will be visually perceived as one star. If we look at it through a telescope, we will clearly see two, or even three components of this system. Other examples of double stars include the Beta Lyrae system, the Beta Persei system (Algol), Sirius and other stars.
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Among the stars that are visible nearby in the sky, a distinction is made between optical doubles and physical doubles. In the first case, two stars are projected onto the celestial sphere next to each other. Although in reality they can be located at a great distance from each other. But physical double stars are actually located in space next to each other. They are not only interconnected by gravitational forces, but also revolve around a common center of mass.
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The idea of the existence of double stars was first put forward by the English scientist and priest John Michell in 1767. And observational confirmation of this hypothesis was published in 1802 by William Herschel. The first stellar pair known since ancient times is Mizar and Alcor, observed in the handle of the “bucket” of the Big Dipper. This stellar pair is a good example of an optical binary star, as Alcor is approximately 12 arcminutes from Mizar.
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When the number of stars in a system connected by mutual gravity turns out to be more than two, then they are called multiples. There are triple, quadruple and even higher multiplicity stars. An example of multiple stars is the triple star α Centauri. Moreover, interestingly, one of the components - Proxima - is the closest star to Earth after the Sun. Stars with less than 10 components are usually classified as multiple stars. If there are more stars in a system, then it is called a star cluster. A classic example is the Pleiades open cluster, visible in the night sky with the naked eye.
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Physical double stars, depending on the method of observing them, are usually divided into several classes. Visual binary stars are double stars whose components can be seen separately (through a telescope or photographed). The ability to observe a star as a visual binary is determined by the resolution of the telescope. Therefore, all known visual double stars are located in the vicinity of the Sun with a very long orbital period (up to several thousand years). And their orbits are comparable in size to the orbits of the giant planets of our Solar System. In this regard, out of over 110,000 such objects, less than a hundred orbits have been determined with great accuracy. The second class of binary systems consists of eclipsing binaries or eclipsing variable stars. They are close pairs, orbiting with a period from several hours to several days in orbits whose semimajor axis is comparable to the stars themselves. This results in the angular distance between stars being very small. Therefore, we cannot see the components of the system separately. However, one can judge that the system is indeed dual by the periodic fluctuations in its brightness. Let us assume that the planes of the stars’ orbits along the line of sight practically coincide. Then, during the revolution of a stellar pair, when one of the components is in front or behind the other, eclipses are observed. The difference between stellar magnitudes at minimum and maximum brightness is called amplitude. And the period of time between two successive smallest minimums is a period of variability.
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Types of double stars First, let's find out which stars are called so. Let's immediately discard the type of double stars that are called "optical double stars." These are pairs of stars that happen to be nearby in the sky, that is, in the same direction, but in space, in fact, they are separated by large distances. We will not consider this type of double. We will be interested in the class of physically binary stars, that is, stars truly bound by gravitational interaction.
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Why are double stars interesting? Firstly, they make it possible to find out the masses of stars, since it is easiest and most reliable to calculate from the visible interaction of two bodies. Direct observations make it possible to find out the total “weight” of the system, and if we add to them the known relationships between the masses of stars and their luminosities, which were discussed above in the story about the fate of stars, then we can find out the masses of the components and test the theory. Single stars do not provide us with such an opportunity. In addition, as was also mentioned earlier, the fate of stars in such systems can be strikingly different from the fate of the same single stars. Celestial pairs, the distances between which are large compared to the size of the stars themselves, at all stages of their lives live according to the same laws as single stars, without interfering with each other. In this sense, their duality does not manifest itself in any way.
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Close pairs: the first exchange of masses Binary stars are born together from the same gas and dust nebula; they have the same age, but often have different masses. We already know that more massive stars live “faster”, therefore, a more massive star will overtake its peer in the process of evolution. It will expand, turning into a giant. In this case, the size of the star can become such that matter from one star (inflated) begins to flow to another. As a consequence, the mass of the initially lighter star can become greater than the initially heavy one! In addition, we will get two stars of the same age, and the more massive star is still on the main sequence, that is, in its center the synthesis of helium from hydrogen is still ongoing, and the lighter star has already used up its hydrogen, and a helium core has formed in it. Let us remember that in the world of single stars this cannot happen. Due to the discrepancy between the age of the star and its mass, this phenomenon is called the Algol paradox, in honor of the same eclipsing binary. The star Beta Lyrae is another pair that is exchanging mass right now.
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Second mass exchange In binary systems, there are also X-ray pulsars emitting in a higher energy wavelength range. This radiation is associated with the accretion of matter near the magnetic poles of a relativistic star. The source of accretion is stellar wind particles emitted by the second star (the solar wind has the same nature). If the star is large, the stellar wind reaches a significant density, and the energy of the X-ray pulsar radiation can reach hundreds and thousands of solar luminosities. An X-ray pulsar is the only way to indirectly detect a black hole, which, as we remember, cannot be seen. And a neutron star is a rare object for visual observation. This is far from all. The second star will also sooner or later inflate, and matter will begin to flow to its neighbor. And this is already the second exchange of matter in a binary system. Having reached large sizes, the second star begins to “return” what was taken during the first exchange.
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If a white dwarf appears in the place of the first star, then as a result of the second exchange, flares can occur on its surface, which we observe as new stars. At one point, when there is too much material falling onto the surface of a very hot white dwarf, the temperature of the gas near the surface rises sharply. This provokes an explosive burst of nuclear reactions. The star's luminosity increases significantly. Such outbreaks can be repeated, and they are called repeated new ones. Repeated flares are weaker than the first, as a result of which the star can increase its brightness tens of times, which we observe from Earth as the appearance of a “new” star. If a white dwarf appears in the place of the first star, then as a result of the second exchange, flares can occur on its surface, which we observe as new stars. At one point, when there is too much material falling onto the surface of a very hot white dwarf, the temperature of the gas near the surface rises sharply. This provokes an explosive burst of nuclear reactions. The star's luminosity increases significantly. Such outbreaks can be repeated, and they are called repeated new ones. Repeated flares are weaker than the first, as a result of which the star can increase its brightness tens of times, which we observe from Earth as the appearance of a “new” star.
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