Presentation Topic: Birth and evolution of stars. Presentation on the topic "evolution of stars" Presentation on astronomy on the topic of evolution of stars
In the starry sky, along with the stars, there are clouds consisting of particles of gas and dust (hydrogen). Some of them are so dense that they begin to shrink under the influence of gravitational attraction. As the gas is compressed, it heats up and begins to emit infrared rays. At this stage, the star is called a PROTOSTAR When the temperature in the protostar's interior reaches 10 million degrees, a thermonuclear reaction begins to convert hydrogen into helium, and the protostar turns into an ordinary star emitting light. Medium-sized stars like the Sun shine for an average of 10 billion years. It is believed that the Sun is still on it, as it is in the middle of its life cycle.
All hydrogen in the course of a thermonuclear reaction turns into helium, a helium layer is formed. If the temperature in the helium layer is less than 100 million Kelvin, no further thermonuclear reaction of the transformation of helium nuclei into nitrogen and carbon nuclei occurs, the thermonuclear reaction does not occur in the center of the star, but only in the hydrogen layer adjacent to the helium layer, while the temperature inside the star gradually increases . When the temperature reaches 100 million Kelvin, a thermonuclear reaction begins in the helium core, while the helium nuclei turn into carbon, nitrogen and oxygen nuclei. The luminosity and size of the star increase, an ordinary star becomes a red giant or supergiant. The circumstellar shell of stars, the mass of which is not more than 1.2 solar masses, gradually expands and eventually breaks away from the core, and the star turns into a white dwarf, which gradually cools and fades. If the mass of a star is about twice the mass of the Sun, then such stars become unstable at the end of their lives and explode, become supernovae, and then turn into neutron stars or a black hole.
At the end of its life, a red giant turns into a white dwarf. A white dwarf is the superdense core of a red giant, made up of helium, nitrogen, oxygen, carbon, and iron. The white dwarf is highly compressed. Its radius is approximately 5000 km, that is, it is approximately equal in size to our Earth. Moreover, its density is about 4 × 10 6 g / cm 3, that is, such a substance weighs four million more than water on Earth. The temperature on its surface is 10000K. The white dwarf cools very slowly and remains to exist until the end of the world.
A supernova is a star at the moment of completion of its evolution in the course of gravitational collapse. The formation of a supernova ends the existence of stars with masses above 8-10 solar masses. In place of a giant supernova explosion remains a neutron star or black hole, and around these objects, the remains of the shells of the exploded star are observed for some time. A supernova explosion in our Galaxy is a rather rare phenomenon. On average, this happens once or twice every hundred years, so it is very difficult to catch the moment when a star emits energy into outer space and flares up at that second like billions of stars.
The extreme forces that occur during the formation of a neutron star compress the atoms so that the electrons pressed into the nuclei combine with protons to form neutrons. Thus, a star is born, almost entirely composed of neutrons. The superdense nuclear liquid, if brought to Earth, would explode like a nuclear bomb, but in a neutron star it is stable due to the enormous gravitational pressure. However, in the outer layers of a neutron star (as, indeed, of all stars), pressure and temperature drop, forming a solid crust about a kilometer thick. It is believed to consist mainly of iron nuclei.
Black holes According to our current understanding of stellar evolution, when a star with a mass greater than about 30 solar masses dies in a supernova explosion, its outer shell flies apart, and the inner layers rapidly collapse towards the center and form a black hole in the place of the star that has used up its fuel reserves. It is practically impossible to identify a black hole of this origin isolated in interstellar space, since it is in a rarefied vacuum and does not manifest itself in any way in terms of gravitational interactions. However, if such a hole was part of a binary star system (two hot stars orbiting around their center of mass), the black hole will still have a gravitational effect on its partner star. The stars will inevitably "flow" in the direction of the black hole. When approaching the fatal boundary, the matter sucked into the funnel of the black hole will inevitably condense and heat up due to more frequent collisions between the particles absorbed by the hole, until it heats up to the radiation energy of waves in the X-ray range. Astronomers can measure the frequency of changes in the intensity of X-rays of this kind and calculate, by comparing it with other available data, the approximate mass of an object that “pulls” matter onto itself. If the mass of an object exceeds the Chandrasekhar limit (1.4 solar masses), this object cannot be a white dwarf, into which our luminary is destined to degenerate. In most cases of observed observations of such double X-ray stars, a neutron star is a massive object. However, there have already been more than a dozen cases where the only reasonable explanation is the presence of a black hole in a binary star system. The Chandrasekhar limit
In the course of thermonuclear reactions occurring in the depths of a star almost throughout its entire life, hydrogen is converted into helium. After a significant part of the hydrogen turns into helium, the temperature at its center increases. When the temperature rises to about 200 million K, helium becomes nuclear fuel, which then turns into oxygen and neon. The temperature in the center of the star gradually increases up to 300 million K. But even at such high temperatures, oxygen and neon are quite stable and do not enter into nuclear reactions. However, after some time, the temperature doubles, now it is already equal to 600 million K. And then neon becomes nuclear fuel, which in the course of reactions turns into magnesium and silicon. The formation of magnesium is accompanied by the release of free neutrons. Free neutrons, reacting with these metals, create atoms of heavier metals - up to uranium - the heaviest of natural elements.
But all the neon in the core has been used up. The core begins to contract, and again the contraction is accompanied by an increase in temperature. The next stage begins, when every two oxygen atoms, when combined, give rise to a silicon atom and a helium atom. Silicon atoms, connecting in pairs, form nickel atoms, which soon turn into iron atoms. Nuclear reactions, accompanied by the emergence of new chemical elements, involve not only neutrons, but also protons and helium atoms. Elements such as sulfur, aluminum, calcium, argon, phosphorus, chlorine, and potassium appear. At temperatures of 2-5 billion K, titanium, vanadium, chromium, iron, cobalt, zinc, and others are born. But of all these elements, iron is the most represented.
With its internal structure, the star now resembles an onion, each layer of which is filled mainly with any one element. With the formation of iron, the star is on the eve of a dramatic explosion. Nuclear reactions occurring in the iron core of a star lead to the conversion of protons into neutrons. In this case, streams of neutrinos are emitted, carrying with them a significant amount of the star's energy into outer space. If the temperature in the core of the star is high, then these energy losses can have serious consequences, since they lead to a decrease in the radiation pressure necessary to maintain the stability of the star. And as a consequence of this, gravitational forces again come into play, designed to deliver the necessary energy to the star. Gravitational forces are compressing the star faster and faster, replenishing the energy carried away by the neutrinos.
As before, the compression of the star is accompanied by an increase in temperature, which eventually reaches 4-5 billion K. Now events are developing somewhat differently. The core, consisting of elements of the iron group, undergoes serious changes: the elements of this group no longer react with the formation of heavier elements, but decay into helium, while emitting a colossal neutron flux. Most of these neutrons are captured by the matter of the outer layers of the star and are involved in the creation of heavy elements. At this stage, the star reaches a critical state. When heavy ones were created chemical elements, energy was released as a result of the fusion of light nuclei. Thus, the star emitted huge amounts of it over hundreds of millions of years. Now the end products of nuclear reactions decay again, forming helium: the star is forced to make up for the energy lost earlier
Betelgeuse is preparing for the explosion (c Arabic. "House of the Twin") - a red supergiant in the constellation Orion. One of the largest stars known to astronomers. If it were placed instead of the Sun, then at its minimum size it would fill the orbit of Mars, and at its maximum it would reach the orbit of Jupiter. The volume of Betelgeuse is almost 160 million times larger than the sun. And it is one of the brightest - its luminosity is times greater than the sun. Its age is only, by space standards, about 10 million years. And this red-hot giant space "Chernobyl" is already on the verge of explosion. The red giant has already begun to agonize and decrease in size. During the observation period from 1993 to 2009, the diameter of the star decreased by 15%, and now it is simply shrinking before our eyes. NASA astronomers promise that the monstrous explosion will increase the brightness of the star by a thousand times. But because of the far distance of light years from us, the catastrophe will not affect our planet in any way. And the result of the explosion will be the formation of a supernova.
What will this rarest event look like from earth? Suddenly, a very bright star will flash in the sky .. Such a space show will last for about six weeks, which means more than a month and a half of "white nights" in certain parts of the planet, the rest of the people will enjoy two or three additional hours of daylight and the delightful spectacle of an exploding star at night. Two or three weeks after the explosion, the star will begin to fade, and in a few years it will finally turn into a Crab-like nebula for an earthly observer. Well, the waves of charged particles after the explosion will reach the Earth in a few centuries, and the inhabitants of the Earth will receive a small (4-5 orders of magnitude less than lethal) dose of ionizing radiation. But you should not worry in any case - as scientists say, there is no threat to the Earth and its inhabitants, but such an event is unique in itself - the last evidence of a supernova explosion on Earth is dated 1054.
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Stars The universe is made up of 98% stars. They are also the main element of the galaxy. “Stars are huge balls of helium and hydrogen, as well as other gases. Gravity pulls them in, and the hot gas pressure pushes them out, creating balance. The energy of a star is contained in its core, where every second helium interacts with hydrogen.”
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The life of stars life path separate organism. Astronomers are unable to trace the life of a single star from beginning to end. Even the shortest-lived stars exist for millions of years - longer than the life of not only one person, but of all mankind. However, scientists can observe many stars at various stages of their development - just born and dying. Based on numerous stellar portraits, they are trying to reconstruct the evolutionary path of each star and write its biography.
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Regions of star formation Regions of star formation. Giant molecular clouds with masses greater than 105 solar masses (more than 6,000 of them are known in the Galaxy) The Eagle Nebula, 6000 light-years away, is a young open star cluster in the constellation Serpens, dark regions in the nebula are protostars
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The Orion Nebula The Orion Nebula is a luminous emission nebula with a greenish tint and is located below Orion's Belt and can be seen even with the naked eye at 1300 light years from us, and a magnitude of 33 light years
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Gravitational contraction Gravitational contraction Compression is a consequence of gravitational instability, Newton's idea. Jeans later determined the minimum size of clouds in which spontaneous contraction can begin. A rather effective cooling of the medium takes place: the released gravitational energy goes into infrared radiation, which escapes into outer space.
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Protostar Protostar As the density of the cloud increases, it becomes opaque to radiation. The temperature of the inner regions begins to rise. The temperature in the interior of a protostar reaches the threshold of thermonuclear fusion reactions. Compression stops for a while.
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Stationary state young star came to the main sequence H-R diagrams the process of hydrogen burnout has begun - the main stellar nuclear fuel is practically not compressed, and energy reserves no longer change slow change chemical composition in its central regions, due to the conversion of hydrogen into helium, the star passes into a stationary state
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Giants and supergiants when hydrogen is completely burnt out, the star leaves the main sequence in the region of giants or, with large masses, supergiants Giants and supergiants
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Gravitational contraction mass of a star< 1,4 массы Солнца: БЕЛЫЙ КАРЛИК электроны обобществляются, образуя вырожденный электронный газ гравитационное сжатие останавливается плотность становится до нескольких тонн в см3 еще сохраняет Т=10^4 К постепенно остывает и медленно сжимается(миллионы лет) окончательно остывают и превращаются в ЧЕРНЫХ КАРЛИКОВ Когда все ядерное топливо выгорело, начинается процесс гравитационного сжатия.
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Dwarfs A white dwarf in a cloud of interstellar dust Two young black dwarfs in the constellation Taurus
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The mass of the star the mass of the star > 1.4 masses of the Sun: the forces of gravitational compression are very high the density of matter reaches a million tons per cm3 huge energy is released - 10 ^ 45 J temperature - 10 ^ 11 K Supernova explosion most of stars are ejected into outer space at a speed of 1000-5000 km / s neutrino flows cool the core of the star - a neutron star
Content
- The birth of the stars
- Star life
- White dwarfs and neutron holes
- Black holes
- The death of the stars
- To acquaint with the action of gravitational forces in the Universe, which lead to the formation of stars.
- Consider the process of evolution of stars.
- Give the concept of the spatial velocity of stars.
- Describe the physical nature of stars.
- Space is often called airless space, believing it to be empty. However, it is not. In interstellar space there is dust and gas, mainly helium and hydrogen, with the latter much more abundant.
- There are even entire clouds of dust and gas in the universe that can collapse under the influence of gravitational forces.
- In the process of compression, part of the cloud will heat up and condense.
- If the mass of the compressing matter is sufficient for nuclear reactions to begin to occur within it during the compression process, then a star is obtained from such a cloud.
- Each "newborn" star, depending on its initial mass, occupies a certain place on the Hertzsprung-Russell diagram - a graph, on one axis of which the color index of the star is plotted, and on the other - its luminosity, i.e. the amount of energy emitted per second.
- The color index of a star is related to the temperature of its surface layers - the lower the temperature, the redder the star, and its color index is greater.
- In the process of evolution, stars change their position on the "spectrum-luminosity" diagram, moving from one group to another. A star spends most of its life on the Main Sequence. To the right and up from it are both the youngest stars and stars that have advanced far along their evolutionary path.
- The lifetime of a star depends mainly on its mass. According to theoretical calculations, the mass of a star can vary from 0,08 before 100 solar masses.
- The greater the mass of a star, the faster hydrogen burns out, and the heavier elements can be formed in the process of thermonuclear fusion in its depths. At a late stage of evolution, when helium burning begins in the central part of the star, it descends from the Main Sequence, becoming, depending on the mass, a blue or red giant.
- But there comes a moment when the star is on the verge of a crisis, it can no longer produce the necessary amount of energy to maintain internal pressure and resist the forces of gravity. The process of uncontrollable compression (collapse) begins.
- As a result of the collapse, stars with a huge density (white dwarfs) are formed. Simultaneously with the formation of a superdense core, the star sheds its outer shell, which turns into a gas cloud - a planetary nebula and gradually dissipates in space.
- A star of greater mass can shrink to a radius of 10 km, turning into a neutron star. One tablespoon of a neutron star weighs 1 billion tons! The last stage in the evolution of an even more massive star is the formation of a black hole. The star shrinks to such a size that the second cosmic velocity becomes equal to the speed of light. In the region of a black hole, space is strongly curved, and time slows down.
- The formation of neutron stars and black holes is necessarily associated with a powerful explosion. A bright point appears in the sky, almost as bright as the galaxy in which it flared up. This is a supernova. Mentions found in ancient chronicles about the appearance in the sky the brightest stars, this is nothing but evidence of colossal cosmic explosions.
- The star loses its entire outer shell, which, expanding at high speed, dissolves without a trace in the interstellar medium after hundreds of thousands of years, and before that we observe it as an expanding gaseous nebula.
- For the first 20,000 years, the expansion of the gas envelope is accompanied by powerful radio emission. During this time, it is a hot plasma ball that has a magnetic field that holds the high-energy charged particles formed in the supernova.
- The more time has passed since the explosion, the weaker the radio emission and the lower the plasma temperature.
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The universe is made up of 98% stars. They are also the main element of the galaxy. “Stars are huge balls of helium and hydrogen, as well as other gases. Gravity pulls them in, and the hot gas pressure pushes them out, creating balance. The energy of a star is contained in its core, where every second helium interacts with hydrogen.”
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The life path of the stars is a complete cycle - birth, growth, a period of relatively calm activity, agony, death, and resembles the life path of an individual organism. Astronomers are unable to trace the life of a single star from beginning to end. Even the shortest-lived stars exist for millions of years - longer than the life of not only one person, but of all mankind. However, scientists can observe many stars at various stages of their development - just born and dying. Based on numerous stellar portraits, they try to reconstruct the evolutionary path of each star and write its biography.
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Regions of star formation. Giant molecular clouds with masses greater than 105 solar masses (more than 6,000 of them are known in the Galaxy) The Eagle Nebula, 6000 light-years away, is a young open star cluster in the constellation Serpens, dark regions in the nebula are protostars
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The Orion Nebula is a glowing emission nebula with a greenish tint and is located below Orion's Belt and can be seen even with the naked eye at 1300 light years from us, and a magnitude of 33 light years
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Gravitational contraction Compression is a consequence of gravitational instability, Newton's idea. Jeans later determined the minimum size of clouds in which spontaneous contraction can begin. A rather effective cooling of the medium takes place: the released gravitational energy goes into infrared radiation, which escapes into outer space.
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Protostar As the density of the cloud increases, it becomes opaque to radiation. The temperature of the inner regions begins to rise. The temperature in the interior of a protostar reaches the threshold of thermonuclear fusion reactions. Compression stops for a while.
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a young star has entered the main sequence of the H-R diagram, the process of hydrogen burnout has begun - the main stellar nuclear fuel is practically not compressed, and energy reserves no longer change a slow change in the chemical composition in its central regions, due to the conversion of hydrogen into helium The star passes into a stationary state
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when hydrogen is completely burnt out, the star leaves the main sequence in the region of giants or, at high masses, supergiants Giants and supergiants
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star mass< 1,4 массы Солнца: БЕЛЫЙ КАРЛИК электроны обобществляются, образуя вырожденный электронный газ гравитационное сжатие останавливается плотность становится до нескольких тонн в см3 еще сохраняет Т=10^4 К постепенно остывает и медленно сжимается(миллионы лет) окончательно остывают и превращаются в ЧЕРНЫХ КАРЛИКОВ Когда все ядерное топливо выгорело, начинается процесс гравитационного сжатия.
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White dwarf in a cloud of interstellar dust Two young black dwarfs in the constellation Taurus
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star mass > 1.4 solar masses: gravitational compression forces are very high density of matter reaches a million tons per cm3 huge energy is released - 10 ^ 45 J temperature - 10 ^ 11 K supernova explosion most of the star is ejected into outer space at a speed of 1000-5000 km / s neutrino flows cool the core of a star - Neutron star
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The universe is made up of 98% stars. They are also the main element of the galaxy.
“Stars are huge balls of helium and hydrogen, as well as other gases. Gravity pulls them in, and the pressure of the hot gas pushes them out, creating an equilibrium. The energy of a star is stored in its core, where helium interacts with hydrogen every second.”
slide 3
The life path of the stars is a complete cycle - birth, growth, a period of relatively calm activity, agony, death, and resembles the life path of an individual organism.
Astronomers are unable to trace the life of a single star from beginning to end. Even the shortest-lived stars exist for millions of years - longer than the life of not only one person, but of all mankind. However, scientists can observe many stars at various stages of their development - just born and dying. Based on numerous star portraits, they are trying to reconstruct the evolutionary path of each star and write its biography.
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Hertzsprung-Russell diagram
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Regions of star formation.
Giant molecular clouds with masses greater than 105 solar masses (more than 6,000 of them are known in the Galaxy)
The Eagle Nebula, 6000 light-years away, is a young open star cluster in the constellation Serpens, the dark regions in the nebula are protostars.
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The Orion Nebula is a glowing emission nebula with a greenish tint and is located below Orion's Belt and can be seen even with the naked eye at 1300 light years from us, and a magnitude of 33 light years
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Gravitational contraction
Compression is a consequence of gravitational instability, Newton's idea.
Jeans later determined the minimum size of clouds in which spontaneous contraction can begin.
A rather effective cooling of the medium takes place: the released gravitational energy goes into infrared radiation, which escapes into outer space.
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protostar
- As the density of the cloud increases, it becomes opaque to radiation.
- The temperature of the inner regions begins to rise.
- The temperature in the interior of a protostar reaches the threshold of thermonuclear fusion reactions.
- Compression stops for a while.
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- a young star has arrived on the main sequence of the H-R diagram
- the process of burning hydrogen - the main stellar nuclear fuel - began
- there is practically no compression, and the energy reserves no longer change
- slow change in the chemical composition in its central regions, due to the conversion of hydrogen into helium
The star goes into a stationary state
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Graph of the evolution of a typical star
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when the hydrogen burns out completely, the star leaves the main sequence in the region of giants or, at high masses, supergiants
Giants and supergiants
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- star mass< 1,4 массы Солнца: БЕЛЫЙ КАРЛИК
- electrons are socialized, forming a degenerate electron gas
- gravitational contraction stops
- density becomes up to several tons per cm3
- still retains T=10^4 K
- gradually cools and slowly shrinks (millions of years)
- finally cool down and turn into BLACK Dwarfs
When all the nuclear fuel has burned out, the process of gravitational compression begins.
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- White dwarf in a cloud of interstellar dust
- Two young black dwarfs in the constellation Taurus
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- star mass > 1.4 solar masses:
- gravitational force is very strong
- the density of a substance reaches a million tons per cm3
- huge energy is released - 10 ^ 45 J
- temperature – 10^11 K
- supernova explosion
- most of the star is ejected into outer space at a speed of 1000-5000 km / s
- streams of neutrinos cool the core of a star -
neutron star
