Everyone knows what the stars look like in the sky. Tiny, glowing lights. In ancient times, people could not come up with an explanation for this phenomenon. The stars were considered the eyes of the gods, the souls of deceased ancestors, guardians and protectors, protecting the peace of man in the darkness of the night. Then no one could have thought that the Sun is also a star.
What is a star
Many centuries passed before people understood what the stars were. Types of stars, their characteristics, ideas about the chemical and physical processes taking place there - this is a new area of \u200b\u200bknowledge. Ancient astronomers could not even imagine that such a luminary was actually not a tiny light at all, but an unimaginable ball of hot gas in which reactions take place
thermonuclear fusion. There is a strange paradox in that dim starlight is the dazzling radiance of a nuclear reaction, and the cozy warmth of the sun is the monstrous heat of millions of kelvins.
All the stars that can be seen in the sky with the naked eye are in the galaxy Milky Way. The sun is also a part of this, and it is located on its outskirts. It is impossible to imagine what the night sky would look like if the Sun were at the center of the Milky Way. After all, the number of stars in this galaxy is more than 200 billion.
A bit about the history of astronomy
Ancient astronomers could also tell unusual and interesting things about the stars in the sky. Already the Sumerians singled out individual constellations and the zodiac circle, they were the first to calculate the division of the full angle by 360 0. They also created the lunar calendar and were able to synchronize it with the solar one. The Egyptians believed that the Earth is in but they knew that Mercury and Venus revolve around the Sun.
In China, astronomy as a science was already practiced at the end of the 3rd millennium BC. e., a
The first observatories appeared in the 12th century. BC e. They studied the moon and solar eclipses, while being able to understand their cause and even calculating the forecast dates, observed meteor showers and comet trajectories.
The ancient Incas knew the differences between stars and planets. There is indirect evidence that they were aware of the Galileans and the visual blurring of the outlines of the disk of Venus, due to the presence of an atmosphere on the planet.
The ancient Greeks were able to prove the sphericity of the Earth, put forward an assumption about the heliocentricity of the system. They tried to calculate the diameter of the Sun, albeit erroneously. But the Greeks were the first to suggest in principle that the Sun more earth, before that everyone, relying on visual observations, believed otherwise. The Greek Hipparchus was the first to create a catalog of luminaries and single out different types stars. The classification of stars in this scientific work based on light intensity. Hipparchus singled out 6 classes of brightness, in total there were 850 luminaries in the catalog.
What did ancient astronomers pay attention to?
The original classification of stars was based on their brightness. After all, this criterion is the only one available to an astronomer armed only with a telescope. The brightest or most visible stars have even received proper names, and each nation has its own. So, Deneb, Rigel and Algol are Arabic names, Sirius is Latin, and Antares is Greek. The polar star in every nation has its own name. This is perhaps one of the most important in the "practical sense" of the stars. Its coordinates in the night sky are unchanged, despite the rotation of the earth. If the rest of the stars move across the sky, going from sunrise to sunset, then the North Star does not change its location. Therefore, it was she who was used by sailors and travelers as a reliable guide. By the way, contrary to popular belief, this is not the brightest star in the sky. The polar star does not stand out in any way - neither in size nor in intensity of luminescence. You can only find it if you know where to look. It is located at the very end of the "ladle handle" Ursa Minor.
What is the star classification based on?
Modern astronomers, answering the question of what types of stars are, are unlikely to mention the brightness of the glow or the location in the night sky. Unless in the order of a historical digression or in a lecture designed for an audience that is very far from astronomy.
The modern classification of stars is based on their spectral analysis. In this case, the mass, luminosity and radius of the celestial body are usually also indicated. All these indicators are given in relation to the Sun, that is, it is its characteristics that are taken as units of measurement.
The classification of stars is based on such a criterion as absolute magnitude. This is the apparent degree of brightness without the atmosphere, conventionally located at a distance of 10 parsecs from the point of observation.
In addition, the brightness variability and the size of the star are taken into account. The types of stars are currently determined by their spectral class and, in more detail, by their subclass. Astronomers Russell and Hertzsprung independently analyzed the relationship between luminosity, absolute temperature surface and spectral type of luminaries. They built a chart with the corresponding coordinate axes and found that the result was not at all chaotic. The luminaries on the graph were located in clearly distinguishable groups. The diagram allows, knowing the spectral type of a star, to determine its absolute magnitude with at least approximate accuracy.
How stars are born
This diagram provided clear evidence in favor of modern theory data evolution celestial bodies. The graph clearly shows that the most numerous class are those belonging to the so-called main sequence stars. The types of stars belonging to this segment are in the most common in this moment point of development in the universe. This is a stage in the development of the luminary, at which the energy expended on radiation is compensated by the energy received during thermonuclear reaction. The length of stay at this stage of development is determined by the mass of the celestial body and the percentage of elements heavier than helium.
The currently accepted theory of stellar evolution states that at the initial
stage of development, the luminary is a rarefied giant gas cloud. Under the influence of its own gravity, it shrinks, gradually turning into a ball. The stronger the compression, the more intense the gravitational energy is converted into heat. The gas heats up, and when the temperature reaches 15-20 million K, a thermonuclear reaction starts in the newborn star. After that, the process of gravitational contraction is suspended.
The main period of a star's life
At first, the reactions of the hydrogen cycle predominate in the bowels of the young luminary. This is the longest period of a star's life. The types of stars that are at this stage of development are presented in the most massive main sequence of the diagram described above. Over time, the hydrogen in the core of the star ends, turning into helium. After that, thermonuclear combustion is possible only at the periphery of the nucleus. The star becomes brighter, its outer layers expand significantly, and the temperature drops. The celestial body turns into a red giant. This period of a star's life
much shorter than the previous one. Her subsequent fate is little known. There are various assumptions, but reliable confirmation of them has not yet been received. The most common theory says that when there is too much helium, the stellar core, unable to withstand its own mass, shrinks. The temperature rises until the helium already enters into a thermonuclear reaction. Monstrous temperatures lead to another expansion, and the star turns into a red giant. Further fate luminaries, according to scientists, depends on its mass. But theories regarding this are just the result of computer simulations, not confirmed by observations.
cooling stars
Presumably, low-mass red giants will shrink, turning into dwarfs and gradually cooling down. Stars medium weight can be transformed into while in the center of such formation the core devoid of external covers will continue to exist, gradually cooling down and turning into a white dwarf. If the central star emitted significant infrared radiation, conditions arise for the activation of a space maser in the expanding gaseous envelope of the planetary nebula.
Massive luminaries, shrinking, can reach such a level of pressure that electrons are literally pressed into atomic nuclei turning into neutrons. Because between
these particles do not have electrostatic repulsion forces, the star can shrink to a size of several kilometers. At the same time, its density will exceed the density of water by 100 million times. Such a star is called a neutron star and is, in fact, a huge atomic nucleus.
Supermassive stars continue to exist, sequentially synthesizing in the process of thermonuclear reactions from helium - carbon, then oxygen, from it - silicon and, finally, iron. At this stage of the thermonuclear reaction, a supernova explosion occurs. Supernovae, in turn, can turn into neutron stars or, if their mass is large enough, continue to collapse to a critical limit and form black holes.
Dimensions
The classification of stars by size can be realized in two ways. The physical size of a star can be determined by its radius. The unit of measurement in this case is the radius of the Sun. There are dwarfs, medium-sized stars, giants and supergiants. By the way, the Sun itself is just a dwarf. The radius of neutron stars can reach only a few kilometers. And in the supergiant, the entire orbit of the planet Mars will fit. The size of a star can also be understood as its mass. It is closely related to the diameter of the star. The larger the star, the lower its density, and vice versa, the smaller the star, the higher the density. This criterion is not viable so much. There are very few stars that would be 10 times larger or smaller than the Sun. Most of the luminaries fit into the interval from 60 to 0.03 solar masses. The density of the Sun, taken as the starting indicator, is 1.43 g/cm 3 . The density of white dwarfs reaches 10 12 g/cm 3 , while the density of rarefied supergiants can be millions of times less than that of the sun.
In the standard classification of stars, the mass distribution scheme is as follows. The small ones include luminaries with a mass of 0.08 to 0.5 solar. To moderate - from 0.5 to 8 solar masses, and to massive - from 8 or more.
Star classification . From blue to white
The classification of stars by color is actually based not on the visible glow of the body, but on spectral characteristics. The emission spectrum of an object is determined chemical composition stars, its temperature depends on it.
The most common is the Harvard classification, created in the early 20th century. According to the then accepted standards, the classification of stars by color involves the division into 7 types.
So, stars with the highest temperature, from 30 to 60 thousand K, are classified as class O luminaries. They are blue in color, the mass of such celestial bodies reaches 60 solar masses (cm), and the radius is 15 solar radii (p. R.). The lines of hydrogen and helium in their spectrum are rather weak. The luminosity of such celestial objects can reach 1 million 400 thousand solar luminosities (s. s.).
Class B stars include luminaries with a temperature of 10 to 30 thousand K. These are celestial bodies of white-blue color, their mass starts from 18 s. m., and the radius - from 7 s. m. The lowest luminosity of objects of this class is 20 thousand s. s., and the hydrogen lines in the spectrum are enhanced, reaching average values.
Class A stars have temperatures ranging from 7.5 to 10 thousand K, they are white. The minimum mass of such celestial bodies starts from 3.1 s. m., and the radius - from 2.1 s. R. The luminosity of objects is in the range from 80 to 20 thousand s. with. The hydrogen lines in the spectrum of these stars are strong, and metal lines appear.
Objects of class F are actually yellow-white, but they look white. Their temperature ranges from 6 to 7.5 thousand K, mass varies from 1.7 to 3.1 cm, radius - from 1.3 to 2.1 s. R. The luminosity of such stars varies from 6 to 80 s. with. The hydrogen lines in the spectrum weaken, the metal lines, on the contrary, increase.
Thus, all types of white stars fall within classes from A to F. Further, according to the classification, yellow and orange luminaries follow.
Yellow, orange and red stars
Types of stars are distributed in color from blue to red, as the temperature decreases and the size and luminosity of the object decreases.
Class G stars, which include the Sun, reach temperatures from 5 to 6 thousand K, they yellow color. The mass of such objects is from 1.1 to 1.7 s. m., radius - from 1.1 to 1.3 s. R. Luminosity - from 1.2 to 6 s. with. The spectral lines of helium and metals are intense, the lines of hydrogen are getting weaker.
Luminaries belonging to class K have a temperature of 3.5 to 5 thousand K. They look yellow-orange, but the true color of these stars is orange. The radius of these objects is in the range from 0.9 to 1.1 s. r., weight - from 0.8 to 1.1 s. m. The brightness ranges from 0.4 to 1.2 s. with. Hydrogen lines are almost imperceptible, metal lines are very strong.
The coldest and smallest stars are of class M. Their temperature is only 2.5 - 3.5 thousand K and they seem to be red, although in reality these objects are orange-red in color. The mass of stars is in the range from 0.3 to 0.8 s. m., radius - from 0.4 to 0.9 s. R. Luminosity - only 0.04 - 0.4 s. with. These are dying stars. Only recently discovered brown dwarfs are colder than them. A separate class M-T was allocated for them.
Stars of different colors
Our Sun is a pale yellow star. In general, the color of the stars is a stunningly diverse palette of colors. One of the constellations is called the "Jewel Box". Scattered across the black velvet of the night sky are sapphire blue stars. Between them, in the middle of the constellation, is a bright orange star.
Differences in the color of the stars
The differences in the color of the stars are explained by the fact that the stars have different temperatures. That's why it happens. Light is wave radiation. The distance between the crests of one wave is called its length. Waves of light are very short. How much? Try dividing an inch into 250,000 equal parts (1 inch equals 2.54 centimeters). Several of these parts make up the length of a light wave.
Despite such an insignificant wavelength of light, the slightest difference between the sizes of light waves dramatically changes the color of the picture that we observe. This is due to the fact that light waves of different lengths are perceived by us as different colors. For example, the wavelength of red is one and a half times longer than the wavelength of blue. White color- this is a beam consisting of photons of light waves of different lengths, that is, from rays of different colors.
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flame color
We know from everyday experience that the color of bodies depends on their temperature. Put the iron poker on the fire. When heated, it first turns red. Then she blushes even more. If the poker could be heated even more without melting it, then it would turn from red to orange, then to yellow, then to white, and finally to blue-white.
The sun is a yellow star. The temperature on its surface is 5,500 degrees Celsius. The temperature on the surface of the hottest blue star exceeds 33,000 degrees.
Physical laws of color and temperature
Scientists have formulated physical laws that relate color and temperature. The hotter the body, the greater the radiation energy from its surface and the shorter the length of the emitted waves. Blue color has a shorter wavelength than red. Therefore, if a body emits in the blue wavelength range, then it is hotter than a body emitting red light. Atoms of the hot gases of stars emit particles called photons. The hotter the gas, the higher the photon energy and the shorter their wave.
The stars that we observe vary both in color and brightness. The brightness of a star depends on both its mass and its distance. And the color of the glow depends on the temperature on its surface. The coldest stars are red. And the hottest ones are a bluish tint. White and blue stars are the hottest, their temperature is higher than the temperature of the Sun. Our star the Sun belongs to the class of yellow stars.
How many stars are in the sky?
It is practically impossible to calculate even at least approximately the number of stars in the part of the Universe known to us. Scientists can only say that in our Galaxy, which is called the "Milky Way", there may be about 150 billion stars. But there are other galaxies too! But much more precisely, people know the number of stars that can be seen from the surface of the Earth with the naked eye. There are about 4.5 thousand such stars.
How are stars born?
If the stars are lit, does anyone need it? In the boundless outer space there are always molecules of the simplest substance in the universe - hydrogen. Somewhere there is less hydrogen, somewhere more. Under the action of forces of mutual attraction, hydrogen molecules are attracted to each other. These processes of attraction can last for a very long time - millions and even billions of years. But sooner or later, hydrogen molecules are attracted so close to each other that a gas cloud is formed. With further attraction, the temperature in the center of such a cloud begins to rise. Millions more years will pass, and the temperature in the gas cloud can rise so much that the reaction of thermonuclear fusion will begin - hydrogen will begin to turn into helium and a new star will appear in the sky. Any star is a hot ball of gas.
The lifespan of stars varies greatly. Scientists have found that the greater the mass of a newborn star, the shorter its lifespan. The lifetime of a star can range from hundreds of millions of years to billions of years.
Light year
A light year is the distance that a ray of light travels in a year at a speed of 300,000 kilometers per second. And there are 31536000 seconds in a year! So, from the star closest to us called Proxima Centauri, a beam of light flies for more than four years (4.22 light years)! This star is 270 thousand times farther from us than the Sun. And the rest of the stars are much further away - tens, hundreds, thousands and even millions of light years from us. This is why stars appear so small to us. And even in the most powerful telescope, unlike the planets, they are always visible as points.
What is a "constellation"?
Since ancient times, people have looked at the stars and seen in the bizarre figures that form groups of bright stars, images of animals and mythical heroes. Such figures in the sky began to be called constellations. And, although in the sky the stars included by people in a particular constellation are visually next to each other, in outer space these stars can be at a considerable distance from each other. The most famous constellations are Ursa Major and Ursa Minor. The fact is that in the constellation Ursa Minor enters the North Star, which is indicated by North Pole our planet Earth. And knowing how to find the North Star in the sky, any traveler and navigator will be able to determine where the north is and navigate the terrain.
supernovae
Some stars at the end of their lives suddenly begin to glow thousands and millions of times brighter than usual, and throw huge masses of matter into the surrounding space. It is customary to say that a supernova explosion occurs. The glow of a supernova gradually fades, and in the end, only a luminous cloud remains in the place of such a star. A similar supernova explosion was observed by ancient astronomers of the Near and Far East July 4, 1054. The decay of this supernova lasted 21 months. Now in the place of this star is the Crab Nebula, known to many astronomy lovers.
Summing up this section, we note that
v. Types of stars
The main spectral classification of stars:
brown dwarfs
Brown dwarfs are a type of star in which nuclear reactions could never compensate for energy losses due to radiation. For a long time brown dwarfs were hypothetical objects. Their existence was predicted in the middle of the 20th century, based on ideas about the processes occurring during the formation of stars. However, in 2004, a brown dwarf was first discovered. To date, a lot of stars of this type have been discovered. Their spectral class is M - T. In theory, one more class is distinguished - denoted by Y.
white dwarfs
Shortly after a helium flash, carbon and oxygen "light up"; each of these events causes a strong rearrangement of the star and its rapid movement along the Hertzsprung-Russell diagram. The size of the star's atmosphere increases even more, and it begins to intensively lose gas in the form of expanding stellar wind streams. The fate of the central part of the star depends entirely on its initial mass: the core of the star can end its evolution as white dwarf(low-mass stars), if its mass in the later stages of evolution exceeds the Chandrasekhar limit - as neutron star(pulsar), but if the mass exceeds the limit of Oppenheimer - Volkov - how black hole. In the last two cases, the completion of the evolution of stars is accompanied by catastrophic events - supernova explosions.
The vast majority of stars, including the Sun, end their evolution by contracting until the pressure of degenerate electrons balances gravity. In this state, when the size of the star decreases by a factor of a hundred and the density becomes a million times higher than that of water, the star is called a white dwarf. It is deprived of sources of energy and, gradually cooling down, becomes dark and invisible.
red giants
Red giants and supergiants are stars with a rather low effective temperature (3000 - 5000 K), but with a huge luminosity. Typical absolute magnitude of such objects? 3m-0m(I and III class luminosity). Their spectrum is characterized by the presence of molecular absorption bands, and the emission maximum falls on the infrared range.
variable stars
A variable star is a star whose brightness has changed at least once in the entire history of its observation. There are many reasons for variability and they can be associated not only with internal processes: if the star is double and the line of sight lies or is at a slight angle to the field of view, then one star, passing through the disk of the star, will outshine it, and the brightness can also change if the light from the star passes through a strong gravitational field. However, in most cases, variability is associated with unstable internal processes. AT latest version The general catalog of variable stars has the following division:
Eruptive variable stars- these are stars that change their brightness due to violent processes and flares in their chromospheres and coronas. The change in luminosity is usually due to changes in the shell or loss of mass in the form of a stellar wind of varying intensity and/or interaction with the interstellar medium.
Pulsating Variable Stars are stars showing periodic expansion and contraction of their surface layers. Pulsations can be radial or non-radial. Radial pulsations of a star leave its shape spherical, while non-radial pulsations cause the star's shape to deviate from spherical, and neighboring zones of the star can be in opposite phases.
Rotating variable stars- these are stars whose brightness distribution over the surface is non-uniform and / or they have a non-ellipsoidal shape, as a result of which, when the stars rotate, the observer fixes their variability. Non-uniformity in surface brightness can be caused by the presence of spots or temperature or chemical inhomogeneities caused by magnetic fields, whose axes do not coincide with the axis of rotation of the star.
Cataclysmic (explosive and nova-like) variable stars. The variability of these stars is caused by explosions, which are caused by explosive processes in their surface layers (novae) or deep in their depths (supernovae).
Eclipsing binary systems.
Optical variable binary systems with hard X-rays
New Variable Types- types of variability discovered during the publication of the catalog and therefore not included in already published classes.
New
A nova is a type of cataclysmic variable. Their brightness does not change as sharply as that of supernovae (although the amplitude can be 9m): a few days before the maximum, the star is only 2m fainter. The number of such days determines which class of novae a star belongs to:
Very fast if this time (referred to as t2) is less than 10 days.
Quick - 11
There is a dependence of the maximum brightness of the nova on t2. Sometimes this relationship is used to determine the distance to a star. The flare maximum behaves differently in different ranges: when a decrease in radiation is already observed in the visible range, an increase still continues in the ultraviolet. If a flash is also observed in the infrared range, then the maximum will be reached only after the brightness in the ultraviolet begins to decline. Thus, the bolometric luminosity during a flare remains unchanged for quite a long time.
Two groups of novae can be distinguished in our Galaxy: new disks (they are brighter and faster on average), and new bulges, which are slightly slower and, accordingly, slightly weaker.
supernovae
Supernovae are stars that end their evolution in a catastrophic explosive process. The term "supernovae" was used to refer to stars that flared up much (by orders of magnitude) stronger than the so-called "new stars". In fact, neither one nor the other is physically new, already existing stars always flare up. But in several historical cases, those stars that were previously almost or completely invisible in the sky flared up, which created the effect of the appearance of a new star. The type of supernova is determined by the presence of hydrogen lines in the flare spectrum. If it is, then a type II supernova, if not, then a type I
Hypernovae
Hypernova - the collapse of an exceptionally heavy star after it no longer has sources to support thermonuclear reactions; in other words, it is a very large supernova. Since the beginning of the 1990s, such powerful explosions of stars have been observed that the force of the explosion exceeded the power of the explosion of an ordinary supernova by about 100 times, and the energy of the explosion exceeded 1046 joules. In addition, many of these explosions were accompanied by very strong gamma-ray bursts. Intensive survey of the sky has found several arguments in favor of the existence of hypernovae, but so far, hypernovae are hypothetical objects. Today, the term is used to describe the explosions of stars with masses from 100 to 150 or more solar masses. Hypernovae could theoretically pose a serious threat to the Earth due to a strong radioactive flare, but at present there are no stars near the Earth that could pose such a danger. According to some reports, 440 million years ago there was an explosion of a hypernova near the Earth. Probably, the short-lived isotope of nickel 56Ni hit the Earth as a result of this explosion.
neutron stars
In stars more massive than the Sun, the pressure of degenerate electrons cannot hold back the collapse of the core, and it continues until most of the particles turn into neutrons packed so tightly that the size of the star is measured in kilometers and the density is 280 trillion. times the density of water. Such an object is called a neutron star; its equilibrium is maintained by the pressure of the degenerate neutron matter.
With a telescope, you can observe 2 billion stars up to 21 magnitudes. There is a Harvard spectral classification of stars. In it, the spectral types are arranged in order of decreasing stellar temperature. Classes are designated by letters of the Latin alphabet. There are seven of them: O - B - A - P - O - K - M.
A good indicator of the temperature of the outer layers of a star is its color. Hot stars of spectral types O and B are blue; stars similar to our Sun (whose spectral type is 02) appear yellow, while stars of spectral classes K and M are red.
Brightness and color of stars
All stars have a color. There are blue, white, yellow, yellowish, orange and red stars. For example, Betelgeuse is a red star, Castor is white, Capella is yellow. By brightness, they are divided into stars of the 1st, 2nd, ... nth magnitude (n max = 25). The term "magnitude" has nothing to do with true dimensions. The magnitude characterizes the light flux coming to Earth from a star. Stellar magnitudes can be both fractional and negative. The magnitude scale is based on the perception of light by the eye. The division of stars into stellar magnitudes according to apparent brightness was carried out by the ancient Greek astronomer Hipparchus (180 - 110 BC). Hipparchus attributed the first magnitude to the brightest stars; he considered the next in brightness gradation (i.e., about 2.5 times weaker) to be stars of the second magnitude; stars weaker than stars of the second magnitude by 2.5 times were called stars of the third magnitude, etc.; stars at the limit of visibility to the naked eye were assigned a sixth magnitude.
With such a gradation of the brightness of the stars, it turned out that the stars of the sixth magnitude are weaker than the stars of the first magnitude by 2.55 times. Therefore, in 1856, the English astronomer N.K. Pogsoy (1829-1891) proposed to consider as stars of the sixth magnitude those that are exactly 100 times weaker than the stars of the first magnitude. All stars are located at different distances from the Earth. It would be easier to compare magnitudes if the distances were equal.
The magnitude that a star would have at a distance of 10 parsecs is called absolute magnitude. The absolute stellar magnitude is indicated - M, and the apparent stellar magnitude - m.
The chemical composition of the outer layers of stars, from which their radiation comes, is characterized by the complete predominance of hydrogen. In second place is helium, and the content of other elements is quite small.
Temperature and mass of stars
Knowing the spectral type or color of a star immediately gives the temperature of its surface. Since stars radiate approximately like absolutely black bodies of the corresponding temperature, the power radiated by a unit of their surface per unit time is determined from the Stefan-Boltzmann law.
The division of stars based on a comparison of the luminosity of stars with their temperature and color and absolute magnitude (Hertzsprung-Russell diagram):
- the main sequence (in the center of it is the Sun - a yellow dwarf)
- supergiants (large in size and high luminosity: Antares, Betelgeuse)
- red giant sequence
- dwarfs (white - Sirius)
- subdwarfs
- white-blue sequence
This division is also based on the age of the star.
The following stars are distinguished:
- ordinary (Sun);
- double (Mizar, Albkor) are divided into:
- a) visual double, if their duality is noticed when observing through a telescope;
- b) multiples - this is a system of stars with a number greater than 2, but less than 10;
- c) optical-double - these are stars that their proximity is the result of a random projection onto the sky, and in space they are far away;
- d) physical binaries are stars that form a single system and circulate under the action of forces of mutual attraction around a common center of mass;
- e) spectroscopic binaries are stars that, when mutually revolving, come close to each other and their duality can be determined from the spectrum;
- e) eclipsing binary - these are stars "which, when mutually revolving, block each other;
new stars- these are stars that existed for a long time, but suddenly flared up. Their brightness increased in a short time by 10,000 times (the amplitude of the change in brightness from 7 to 14 magnitudes).
supernovae- these are stars that were invisible in the sky, but suddenly flashed and increased in brightness 1000 times relative to ordinary new stars.
Pulsar- a neutron star that occurs during a supernova explosion.
Data on the total number of pulsars and their lifetimes indicate that, on average, 2-3 pulsars are born per century, which approximately coincides with the frequency of supernova explosions in the Galaxy.
Star evolution
Like all bodies in nature, stars do not remain unchanged, they are born, evolve, and finally die. Astronomers used to think that it took millions of years for a star to form from interstellar gas and dust. But in recent years, photographs have been taken of a region of the sky that is part of the Great Nebula of Orion, where a small cluster of stars has appeared over the course of several years. In the photographs of 1947, a group of three star-like objects was recorded in this place. By 1954 some of them had become oblong, and by 1959 these oblong formations had disintegrated into individual stars. For the first time in the history of mankind, people observed the birth of stars literally before our eyes.
In many parts of the sky, there are conditions necessary for the appearance of stars. When studying photographs of the hazy regions of the Milky Way, it was possible to find small black spots of irregular shape, or globules, which are massive accumulations of dust and gas. These gas and dust clouds contain dust particles that very strongly absorb the light coming from the stars behind them. The size of the globules is huge - up to several light years in diameter. Despite the fact that the matter in these clusters is very rarefied, their total volume is so large that it is quite enough to form small clusters of stars close in mass to the Sun.
In a black globule, under the influence of radiation pressure emitted by surrounding stars, the matter is compressed and compacted. Such compression proceeds for some time, depending on the sources of radiation surrounding the globule and the intensity of the latter. The gravitational forces arising from the concentration of mass in the center of the globule also tend to compress the globule, causing matter to fall towards its center. Falling, particles of matter acquire kinetic energy and heat up the gas and cloud.
The fall of matter can last hundreds of years. At first, it occurs slowly, unhurriedly, since the gravitational forces that attract particles to the center are still very weak. After some time, when the globule becomes smaller and the gravitational field increases, the fall begins to occur faster. But the globule is huge, no less than a light year in diameter. This means that the distance from its outer border to the center can exceed 10 trillion kilometers. If a particle from the edge of the globule starts to fall towards the center at a speed slightly less than 2 km/s, then it will reach the center only after 200,000 years.
The lifespan of a star depends on its mass. Stars With a mass less than that of the Sun use their nuclear fuel very sparingly and can shine for tens of billions of years. The outer layers of stars like our Sun, with masses no greater than 1.2 solar masses, gradually expand and, in the end, completely leave the core of the star. In place of the giant remains a small and hot white dwarf.
Many people think that all the stars in the sky are white. (Except for the Sun, which, of course, yellow.) Surprisingly, but in fact it's just the opposite: ours, and the stars come in different colors - bluish, white, yellowish, orange and even red!
Another question, Can you see the color of stars with the naked eye?? Dim stars appear white simply because they are too weak to excite cones in the retina of our eyes - special receptor cells responsible for color vision. Rods sensitive to weak light do not distinguish colors. That is why in the dark all cats are gray and all stars are white.
bright star colors
What about bright stars?
Let's look at the constellation of Orion, or rather, at its two brightest stars, Rigel and Betelgeuse. (Orion is the central constellation of the winter sky. It is observed in the evenings in the south from late November to March.)
The star Betelgeuse stands out among others in the constellation Orion with its reddish tint. Photo: Bill Dickinson/APOD
Even a cursory glance is enough to notice the red color of Betelgeuse and the bluish-white color of Rigel. This is not an apparent phenomenon - the stars do have different colors. The difference in color is determined only by the temperature on the surfaces of these stars. White stars are hotter than yellow stars, and yellow stars are hotter than orange stars. The hottest stars are bluish white, while the coldest are red. Thus, Rigel is much hotter than Betelgeuse.
What color is Rigel really?
Sometimes, though, it's not so obvious. On a frosty or windy night, when the air is restless, you can observe a strange thing - Rigel quickly changes its brightness (in other words, flickers) and shimmers in different colors! Sometimes it looks like it's blue, sometimes it looks like it's white, and then it flashes red for a moment! It turns out that Rigel is not a bluish-white star at all - it is generally unclear what color it is!
Blue Rigel and reflection nebula Witch's Head. Photo: Michael Heffner/Flickr.com
The responsibility for this phenomenon lies entirely with the Earth's atmosphere. Low above the horizon (and Rigel never rises high in our latitudes) the stars often twinkle and shimmer in different colors. Their light passes through a very large thickness of the atmosphere before reaching our eyes. Along the way, it is refracted and deflected in layers of air with different temperatures and densities, creating the effect of trembling and rapid color changes.
The best example of a star that shimmers in different colors is white Sirius, which is located in the sky next to Orion. Sirius is the brightest star in the night sky, and therefore its twinkling and rapid color change are much more noticeable than those of the stars in the neighborhood.
Although stars come in a variety of colors, white and reddish are best seen with the naked eye. Of all the bright stars, perhaps only Vega looks distinctly bluish.
Vega looks like a sapphire in a telescope. Photo: Fred Espanak
Colors of stars in telescopes and binoculars
Optical instruments - telescopes, binoculars and spyglasses - will show a much brighter and wider palette of star colors. You will see bright orange and yellow stars, bluish white, yellowish white, golden and even greenish stars! How real are these colors?
Basically they are all real! Truth, there are no green stars in nature(why is a separate question), this is an optical illusion, although very beautiful! Observation of greenish and even emerald green stars is only possible when there is a yellow or yellowish-orange star very close.
A reflecting telescope reproduces colors much more accurately than a refractor., since lens telescopes suffer to varying degrees of chromatic aberration, and reflector mirrors reflect light of all colors equally.
It is very interesting to observe the multi-colored stars, first with the naked eye, and then with binoculars or a telescope. (When looking through a telescope, use the lowest magnification.)
The table below shows the colors for 8 bright stars. The brightness of the stars is given in stellar magnitudes. The letter v means that the brightness of the star is variable - for physical reasons it shines either brighter or dimmer.
| Star | Constellation | Shine | Colour | Evening visibility |
|---|---|---|---|---|
| Sirius | Big Dog | -1.44 | White, but often shimmers and shimmers in different colors due to atmospheric conditions | November - March |
| Vega | Lyra | 0.03 | blue | All year round |
| Chapel | Auriga | 0.08 | yellow | All year round |
| Rigel | Orion | 0.18 | Bluish white, but often highly shimmery and iridescent due to atmospheric conditions | November - April |
| Procyon | Small Dog | 0.4 | White | November - May |
| Aldebaran | Taurus | 0.87 | Orange | October - April |
| Pollux | Twins | 1.16 | pale orange | November - June |
| Betelgeuse | Orion | 0.45v | orange red | November - April |
Colorful stars in the December sky
In December, you can find a whole dozen bright colored stars! We have already talked about the red Betelgeuse and the bluish-white Rigel. On exceptionally calm nights, Sirius is striking in its whiteness. Star Chapel in the constellation Auriga to the naked eye it seems almost white, but in a telescope it reveals a distinct yellowish tint.
Be sure to take a look at Vega, which from August to December is visible in the evenings high in the sky in the south, and then in the west. It is not for nothing that Vega is called the heavenly sapphire - its blue color is so deep when observed through a telescope!
Finally at the star Pollux from the constellation of Gemini you will find a pale orange glow.
Pollux is the brightest star in the constellation Gemini. Photo: Fred Espanak
In the end, I note that the colors of the stars that we observe visually depend largely on the sensitivity of our eyes and subjective perception. Perhaps you will object to me on all points and say that the color of Pollux is deep orange, and Betelgeuse is yellowish red. Do an experiment! Look at the stars in the table above for yourself - with the naked eye and through an optical instrument. Rate their color!
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