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DOUBLE S S S
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Types of double stars
First, let's find out which stars are called this. 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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Center of mass position
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 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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Spectral double stars
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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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: first mass exchange
Binary stars are born together from the same gas-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.
Slide 13
Second mass exchange
In binary systems, there are also X-ray pulsars that emit 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.
Slide 14
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.
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Astronomical double 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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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.
Slide 10
Slide description:
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.
Slide 14
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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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Slide text: 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.
Slide text: 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.
Slide text: 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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Slide text: The brilliance of double stars Often stars in pairs differ greatly in brightness, with a dim star being 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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Slide text: 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.
Slide text: 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.
Slide No. 10
Slide text: 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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Slide text: Matter from an inflated star, flowing onto a 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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Slide text: Second mass exchange In binary systems, there are also X-ray pulsars that emit 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.
Slide No. 14
Slide text: 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.
Slide No. 15
Slide text: 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.
Slide No. 16
Slide text: Astronomical double stars
STARS
First, let's find out which stars are called this. 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.
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.
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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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.
Slide 10
Slide description:
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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