"Neutron Star" - 7. 8. Measured masses of neutron stars. Stars with higher central density and higher mass turn out to be unstable. The internal structure of neutron stars. 2. Direct introduction of multiparticle forces in isovector channels: Relativistic Mean Field Model (RMF). Introduction of multiparticle forces.
"Double Stars" - Visually astrometrically binary eclipsing binaries are spectroscopic binaries. First, let's find out which stars are called that. What is interesting double stars. Single stars do not provide us with such an opportunity. The last type of binaries are spectroscopic binaries. Spectral doubles. Eclipsing binaries.
"The mass of stars" - The mass is almost equal to the sun, and in size 2.5 times larger than the Earth. Energy source of the sun and stars. Main sequence. The densities of main sequence stars are comparable to the solar density. The masses of stars are 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 of Orion, Canis Major and Canis Minor.
"Constellation Astronomy" - Based primarily on observations. But not only Akida fell in love with Galatea. Spiral galaxy M74. The names of the constellations were associated with myths, the names of gods, the names of instruments and mechanisms. Let's start our acquaintance with the constellations from the summer sky. Ursa Minor. Zodiacs. In the north hangs an inverted bucket of the Big Dipper.
Mizar and Alcor are not only projected side by side onto the celestial sphere, but also move around a common center of mass. The circulation period is about 2 billion years. There are many double and multiple stars in the Galaxy. Mira - Omicron Ceti - double star. Photo a shows the components of a binary star at a distance of 0.6 ". Photographs b and c show that their shape is not spherical, a tail is visible from Mira towards the smaller star. This may be due to the gravitational interaction of Mira Ceti with your companion ac b
Multiple systems often appear to the naked eye as single stars. With good binoculars and telescopes, you can see their duality or multiplicity. The star ε Lyrae is a physical system consisting of two close star pairs ε 1 and ε 2. Multiple stars
The star θ Orionis is a complex multiple system. θ 1 and θ 2 when viewed through a small telescope appear as a quadruple system and a triple system. With a strong telescope, even more stars can be seen. The whole system is called the Trapezium of Orion. Trapeze of Orion (center)
An example of a multiple system is α Centauri (Rigil Centaurus), located 4.3 light years from the Sun. Component C has coordinates α = 14 h 26 m, δ = –62 ° 28 "and is the closest star to the Sun. Its proper name is Proxima Centauri. Rigil Centaurus is the star system closest to the Sun
The law of universal gravitation and the laws of Kepler generalized by Newton are applicable to systems of binary stars. This makes it possible to estimate the masses of stars in binary systems. According to Kepler's third law, you can write the proportion where m 1 and m 2 are the masses of two stars with a period of revolution P, A is the semi-major axis of the orbit of a star revolving around another star. The masses M and m are the masses of the Sun and the Earth, T = 1 year, and is the distance from the Earth to the Sun. This formula gives the sum of the masses of the binary components, i.e. members of this system. α is the angular distance between the components π is the annual parallax of the star If we determine the distances of stars to their common center of gravity from observations, then we can determine the mass of each star.
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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 binaries that is called "optical binaries". These are pairs of stars that happened to be side by side 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 doubles. We will be interested in the class of physically binary, that is, stars really connected by gravitational interaction.
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Why are double stars interesting? First, they make it possible to find out the masses of stars, since it is most easily and most reliably calculated from the apparent interaction of two bodies. Direct observations allow us 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, 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 appear in any way.
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Close pairs: the first mass exchange The stars of a binary are born together from the same gas and dust nebula, they have the same age, but often 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 the matter from one star (swollen) will begin to flow to another. As a consequence, the mass of the initially lighter star may become larger 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, helium fusion from hydrogen continues in its center, and the lighter star has already used up its hydrogen, a helium core has formed in it. Recall that in a world of single stars this cannot happen. For 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 Beta Lyra star is another pair that is undergoing a mass exchange right now.
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Second Mass Exchange Binary systems also contain 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 the particles of the stellar wind emitted by the second star (the nature of the solar wind is the same). If the star is large, the stellar wind reaches a significant density, the radiation energy of an X-ray pulsar 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. Yes, and a neutron star is the rarest object for visual observation. This is far from everything. The second star will also swell sooner or later, and the matter will begin to flow to the neighbor. And this is already the second exchange of matter in the binary system. Having reached a large size, 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 moment, when there is too much material that has fallen 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 luminosity of the star increases significantly. Such outbreaks can be repeated, and they are already called repeated new ones. Repeated outbursts are weaker than the first ones, as a result of which the star can increase its brightness by dozens of times, which we observe from the 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 moment, when there is too much material that has fallen 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 luminosity of the star increases significantly. Such outbreaks can be repeated, and they are already called repeated new ones. Repeated outbursts are weaker than the first ones, as a result of which the star can increase its brightness by dozens of times, which we observe from the Earth as the appearance of a "new" star.
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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 binaries that is called "optical binaries". These are pairs of stars that happened to be side by side 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 doubles. We will be interested in the class of physically binary, that is, stars really connected by gravitational interaction.
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Position of the center of mass Physically, binary stars rotate in ellipses around a common center of mass. However, if we count 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 have taken a more massive blue star as the 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 a common misconception that it is often assumed that a more massive star attracts a star with a low mass more strongly than vice versa. Any two objects attract each other equally. But an object with a large mass is more difficult to budge. And although a stone falling to 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, it is always possible to single out a binary subsystem and a third star rotating around this pair. In a system of four stars, there may be two binary subsystems rotating around a common center of mass. In other words, in nature, stable multiple systems always reduce to two-term systems. The notorious Alpha Centauri, considered by many to be the closest star to us, belongs to the three-star system, but in fact, the third faint 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 the star is double is visible through a telescope. Such binaries are called visual binaries (not to be confused with optical binaries!). 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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Brilliance of double stars Often stars in pairs differ greatly in brilliance, a dim star is overshadowed by the brilliance of a bright one. Sometimes in such cases, astronomers learn about the duality of a star by deviations in the motion of a bright star under the influence of an invisible companion from the trajectory calculated for a single star in space. Such pairs are called astrometric binaries. In particular, Sirius for a long time belonged to this type of double, until the power of the telescopes made it possible to see the 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, as it were, edged towards us. Here the stars will periodically outshine each other, the brightness of the entire pair will change with the same period. This type of binaries is called eclipsing binaries. 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 (Devil's Eye) in the constellation Perseus.
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Spectral binaries The last type of binaries are spectroscopic binaries. Their duality is determined by studying the spectrum of the star, in which periodic shifts of absorption lines are noticed or it is seen 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? First, they make it possible to find out the masses of stars, since it is most easily and most reliably calculated from the apparent interaction of two bodies. Direct observations allow us 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, 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 appear in any way.
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Close pairs: the first mass exchange The stars of a binary are born together from the same gas and dust nebula, they have the same age, but often different masses. We already know that more massive stars live "faster", therefore, a more massive star in the process of evolution will overtake its peer. It will expand, turning into a giant. In this case, the size of the star can become such that the matter from one star (swollen) will begin to flow to another. As a consequence, the mass of the initially lighter star may become larger 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, helium fusion from hydrogen continues in its center, and the lighter star has already used up its hydrogen, a helium core has formed in it. Recall that in a world of single stars this cannot happen. For 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 Beta Lyra star is another pair that is undergoing a mass exchange right now.
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The matter from the swollen star, flowing onto the less massive component, does not fall on it immediately (this is hindered by the mutual rotation of the stars), but first forms a rotating disk of matter around the smaller star. Friction forces in this disk will reduce the speed of matter particles, and it will settle on the surface of the star. Such a process is called accretion, and the resulting disk is called accretion. As a result, an initially more massive star has an unusual chemical composition: all the hydrogen in its outer layers flows to another star, and only a helium core with impurities of heavier elements remains. Such a star, called a helium star, rapidly evolves to form a white dwarf or relativistic star, depending on its mass. At the same time, an important change took place in the binary system as a whole: the initially more massive star gave way to this leadership.
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Second Mass Exchange Binary systems also contain 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 the particles of the stellar wind emitted by the second star (the nature of the solar wind is the same). If the star is large, the stellar wind reaches a significant density, the radiation energy of an X-ray pulsar 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. Yes, and a neutron star is the rarest object for visual observation. This is far from everything. The second star will also swell sooner or later, and the matter will begin to flow to the neighbor. And this is already the second exchange of matter in the binary system. Having reached a large size, 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 that has fallen 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 luminosity of the star increases significantly. Such outbreaks can be repeated, and they are already called repeated new ones. Repeated outbursts are weaker than the first ones, as a result of which the star can increase its brightness by dozens of times, which we observe from the Earth as the appearance of a "new" star.
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Another outcome in a white dwarf system is a supernova explosion. As a result of the flow of matter from the second star, the white dwarf may reach a limiting mass of 1.4 solar masses. If this is already an iron white dwarf, then it will not be able to keep the gravitational contraction and will explode. Supernova explosions in binary systems are very similar in brightness and development to each other, since stars of the same mass always explode - 1.4 solar. Recall that in single stars this critical mass is reached by the central iron core, while 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 flashes have the same luminosity. By noticing them in distant galaxies, we can calculate distances far greater than can be determined using stellar parallax or Cepheids. The loss of a significant part 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.
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Binary Stars The Sun is a single star. But sometimes two or more stars are located close to each other and revolve one around the other. They are called double or multiple stars. There are a lot of them in the Galaxy. So, the star Mizar in the constellation Ursa Major has a satellite - Alcor. Depending on the distance between them, binary stars revolve around each other quickly or slowly, and the period of revolution can range from several days to many thousands of years. Some binary stars are turned to the Earth by the edge of the plane of their orbit, then one star regularly outshines the other. At the same time, the overall brightness of the stars weakens. We perceive this as a change in the brightness of the star. For example, the "devil star" Algol in the constellation Perseus has been known since ancient times as a variable star. Every 69 hours - such is the period of revolution of stars in this binary system - there is an eclipse of a brighter star by its cold and less bright neighbor. From the Earth, this is perceived as a decrease in its brilliance. Ten hours later, the stars diverge, and the brightness of the system again becomes maximum.
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