What determines the color of a star in the sky. What are the stars. Systematization of stars. From blue to white

Spectral classification of stars and dependence of color on their surface temperature

The color of a star is determined by the difference between its magnitudes. By general agreement, these scales are chosen so that a white star, like Sirius, has the same magnitude on both scales. The difference between the photographic and photovisual quantities is called the color index of a given star. For such blue stars as Rigel, this number will be negative, since such stars on an ordinary plate give a greater blackening than on a yellow-sensitive one.

For red stars like Betelgeuse, the color index reaches + 2-3 magnitudes. This measurement of color is also a measurement of the surface temperature of the star, with blue stars being much hotter than red ones.

Since color indices can be obtained quite easily even for very faint stars, they are of great importance when studying the distribution of stars in space.

Instruments are among the most important tools for studying stars. Even the most superficial look at the spectra of stars reveals that they are not all the same. The Balmer lines of hydrogen are strong in some spectra, weak in some, and absent altogether in some.

It soon became clear that the spectra of stars can be divided into a small number of classes, gradually passing into each other. The current spectral classification was developed at the Harvard Observatory under the direction of E. Pickering.

At first, the spectral classes were designated in Latin letters in alphabetical order, but in the process of refining the classification, the following designations for successive classes were established: O, B, A, F, G, K, M. In addition, a few unusual stars are combined into classes R, N and S , and individual individuals who do not fit into this classification at all are designated by the symbol PEC (peculiar - special).

It is interesting to note that the arrangement of stars by class is also an arrangement by color.

• Class B stars, to which Rigel and many other stars in Orion belong, are blue;
• classes O and A - white (Sirius, Deneb);
• classes F and G - yellow (Procyon, Capella);
• classes K and M - orange and red (Arcturus, Aldebaran, Antares, Betelgeuse).

Arranging the spectra in the same order, we see how the maximum of the emission intensity shifts from the violet to the red end of the spectrum. This indicates a decrease in temperature as one moves from class O to class M. A star's place in the sequence is determined more by its surface temperature than by its chemical composition. It is generally accepted that the chemical composition is the same for the vast majority of stars, but different surface temperatures and pressures cause large differences in stellar spectra.

Blue class O stars are the hottest. Their surface temperature reaches 100,000°C. Their spectra are easily recognizable by the presence of some characteristic bright lines or by the propagation of the background far into the ultraviolet region.

They are directly followed class B blue stars, are also very hot (surface temperature 25,000°C). Their spectra contain lines of helium and hydrogen. The former weaken, while the latter strengthen in the transition to class A.

IN classes F and G(a typical G-class star is our Sun) the lines of calcium and other metals, such as iron and magnesium, gradually increase.

IN class K calcium lines are very strong, and molecular bands also appear.

Class M includes red stars with surface temperatures below 3000°C; bands of titanium oxide are visible in their spectra.

Classes R, N and S belong to the parallel branch of cool stars whose spectra contain other molecular components.

For the connoisseur, however, there is a very big difference between "cold" and "hot" class B stars. In a precise classification system, each class is subdivided into several more subclasses. The hottest class B stars are subclass VO, stars with an average temperature for this class - k subclass B5, the coldest stars - to subclass B9. The stars are directly behind them. subclass AO.

The study of the spectra of stars turns out to be very useful, since it makes it possible to roughly classify stars according to their absolute magnitudes. For example, the VZ star is a giant with an absolute magnitude of approximately -2.5. It is possible, however, that the star will be ten times brighter (absolute value - 5.0) or ten times fainter (absolute value 0.0), since it is impossible to give a more accurate estimate from the spectral type alone.

When establishing a classification of stellar spectra, it is very important to try to separate giants from dwarfs within each spectral class or, where this division does not exist, to single out from the normal sequence of giants stars that have too high or too low luminosity.

Everyone knows three states of matter - solid, liquid and gaseous.. What happens to a substance when it is sequentially heated to high temperatures in a closed volume? - Sequential transition from one state of aggregation to another: solid - liquid - gas(due to the increase in the speed of movement of molecules with increasing temperature). With further heating of the gas at temperatures above 1,200 ºС, the disintegration of gas molecules into atoms begins, and at temperatures above 10,000 ºС, partial or complete disintegration of gas atoms into their constituent elementary particles - electrons and atomic nuclei. Plasma is the fourth state of matter, in which the molecules or atoms of matter are partially or completely destroyed by high temperatures or for other reasons. 99.9% of the matter in the Universe is in the state of plasma.

Stars are a class of cosmic bodies with a mass of 10 26 -10 29 kg. A star is a hot plasma spherical cosmic body, which is, as a rule, in hydrodynamic and thermodynamic equilibrium.

If the equilibrium is disturbed, the star begins to pulsate (its dimensions, luminosity and temperature change). The star becomes a variable star.

variable star is a star whose brilliance (apparent brightness in the sky) changes over time. The reasons for the variability can be physical processes in the interior of the star. Such stars are called physical variables(for example, δ Cephei. Variable stars similar to it began to be called Cepheids).

meet and eclipse variables stars whose variability is caused by mutual eclipses of their components(for example, β Perseus - Algol. Its variability was first discovered in 1669 by the Italian economist and astronomer Geminiano Montanari).

Eclipsing variable stars are always double, those. composed of two closely spaced stars. Variable stars on star charts are indicated by a circled circle:

Stars are not always balls. If the star rotates very quickly, then its shape is not spherical. The star shrinks from the poles and becomes like a tangerine or a pumpkin (for example, Vega, Regulus). If the star is double, then the mutual attraction of these stars to each other also affects their shape. They become ovoid or melon-shaped (for example, components of the binary star β Lyra or Spica):

Stars are the main inhabitants of our Galaxy (our Galaxy is written with a capital letter). It contains about 200 billion stars. With the help of even the largest telescopes, only half a percent of the total number of stars in the Galaxy can be seen. More than 95% of all matter observed in nature is concentrated in stars. The remaining 5% are interstellar gas, dust, and all non-luminous bodies.

Apart from the Sun, all the stars are so far from us that even in the largest telescopes they are observed in the form of luminous points of different colors and brilliance. The closest to the Sun is the α Centauri system, which consists of three stars. One of them - a red dwarf called Proxima - is the closest star. It is 4.2 light years away. To Sirius - 8.6 St. years, to Altair - 17 St. years. To Vega - 26 St. years. To the North Star - 830 St. years. To Deneb - 1,500 St. years. For the first time, the distance to another star (it was Vega) in 1837 was able to determine V.Ya. Struve.

The first star that managed to get an image of the disk (and even some spots on it) is Betelgeuse (α Orion). But this is because Betelgeuse is 500-800 times larger than the Sun in diameter (the star is pulsating). An image of the disk of Altair (α Eagle) was also obtained, but this is because Altair is one of the nearest stars.

The color of stars depends on the temperature of their outer layers. Temperature range - from 2000 to 60000 °C. The coldest stars are red and the hottest are blue. By the color of the star, you can judge how hot its outer layers are.

Examples of red stars: Antares (α Scorpio) and Betelgeuse (α Orion).

Examples of orange stars: Aldebaran (α Taurus), Arcturus (α Bootes) and Pollux (β Gemini).

Examples of yellow stars: Sun, Capella (α Aurigae) and Toliman (α Centauri).

Examples of yellowish-white stars are Procyon (α Minor Canis) and Canopus (α Carinae).

Examples of white stars are Sirius (α Canis Major), Vega (α Lyrae), Altair (α Eagle) and Deneb (α Cygnus).

Examples of bluish stars: Regulus (α Leo) and Spica (α Virgo).

Due to the fact that very little light comes from the stars, the human eye is able to distinguish color shades only in the brightest of them. Through binoculars and even more so through a telescope (they capture more light than the eye), the color of the stars becomes more noticeable.

Temperature increases with depth. Even the coldest stars in the center reach millions of degrees. The Sun has about 15,000,000 ° C in the center (they also use the Kelvin scale - the scale of absolute temperatures, but when it comes to very high temperatures, the difference of 273 º between the Kelvin and Celsius scales can be neglected).

What is it that heats up the stellar interior so much? It turns out that there are thermonuclear processes, resulting in a huge amount of energy being released. In Greek, "thermos" means warm. The main chemical element that stars are made of is hydrogen. It is he who is the fuel for thermonuclear processes. In these processes, the nuclei of hydrogen atoms are converted into the nuclei of helium atoms, which is accompanied by the release of energy. The number of hydrogen nuclei in the star decreases, while the number of helium nuclei increases. Over time, other chemical elements are synthesized in the star. All the chemical elements that make up the molecules of various substances were once born in the depths of stars."Stars are the past of man, and man is the future of the star," - this is sometimes figuratively said.

The process by which a star emits energy in the form of electromagnetic waves and particles is called radiation. Stars radiate energy not only in the form of light and heat, but also other types of radiation - gamma rays, X-rays, ultraviolet, radio radiation. In addition, stars emit streams of neutral and charged particles. These streams form the stellar wind. Stellar wind is the process of outflow of matter from stars into outer space. As a result, the mass of stars is constantly and gradually decreasing. It is the stellar wind from the Sun (solar wind) that leads to the appearance of auroras on Earth and other planets. It is the solar wind that deflects the tails of comets away from the Sun.

Stars, of course, do not appear from emptiness (the space between stars is not an absolute vacuum). The material is gas and dust. They are unevenly distributed in space, forming shapeless clouds of very low density and enormous extent - from one or two to tens of light years. Such clouds are called diffuse gas and dust nebulae. The temperature in them is very low - about -250 °C. But not every gas-dust nebula produces stars. Some nebulae can exist for a long time without stars. What conditions are necessary for the start of the process of the birth of stars? The first is the mass of the cloud. If there is not enough matter, then, of course, the star will not appear. Second, compactness. In a cloud that is too extended and loose, the processes of its compression cannot begin. Well, and thirdly, we need a seed - i.e. a bunch of dust and gas, which will later become the embryo of a star - a protostar. protostar is a star at the final stage of its formation. If these conditions are met, then gravitational compression and heating of the cloud begins. This process ends star formation- the emergence of new stars. This process takes millions of years. Astronomers have found nebulae in which the process of star formation is in full swing - some stars have already lit up, some are in the form of embryos - protostars, and the nebula is still preserved. An example is the Great Nebula of Orion.

The main physical characteristics of a star are luminosity, mass and radius.(or diameter), which are determined from observations. Knowing them, as well as the chemical composition of the star (which is determined by its spectrum), it is possible to calculate the model of the star, i.e. physical conditions in its depths, to explore the processes that take place in it.Let us dwell in more detail on the main characteristics of stars.

Weight. The mass can be directly estimated only by the gravitational effect of the star on the surrounding bodies. The mass of the Sun, for example, was determined from the known periods of revolution of the planets around it. Other stars do not directly observe planets. Reliable measurement of mass is possible only for binary stars (in this case, Kepler's law generalized by Newton III is used, no and then the error is 20-60%). Approximately half of all stars in our galaxy are binary. The masses of stars range from ≈0.08 to ≈100 solar masses.Stars with a mass less than 0.08 of the mass of the Sun do not exist, they simply do not become stars, but remain dark bodies.Stars with a mass greater than 100 solar masses are extremely rare. Most stars have masses less than 5 solar masses. The fate of the star depends on the mass, i.e. the scenario according to which the star develops, evolves. Small cold red dwarfs use hydrogen very economically and therefore their life spans hundreds of billions of years. The life span of the Sun - a yellow dwarf - is about 10 billion years (the Sun has already lived about half of its life). Massive supergiants consume hydrogen quickly and die out within a few million years after their birth. The more massive the star, the shorter its life path.

The age of the universe is estimated at 13.7 billion years. Therefore, stars older than 13.7 billion years do not yet exist.

• Stars with mass 0,08 the masses of the Sun are brown dwarfs; their fate is constant contraction and cooling with the cessation of all thermonuclear reactions and transformation into dark planet-like bodies.

• Stars with mass 0,08-0,5 the masses of the Sun (these are always red dwarfs) after the consumption of hydrogen begin to slowly shrink, while heating up and becoming a white dwarf.
  

• Stars with mass 0,5-8 masses of the Sun at the end of life turn first into red giants, and then into white dwarfs. In this case, the outer layers of the star are scattered in outer space in the form planetary nebula. A planetary nebula is often spherical or ring shaped.
  

• Stars with mass 8-10 solar masses can explode at the end of their lives, or they can age quietly, first turning into red supergiants, and then into red dwarfs.

• Stars with a mass greater than 10 masses of the Sun at the end of their life path, they first become red supergiants, then explode as supernovae (a supernova is not a new, but an old star) and then turn into neutron stars or become black holes.
  

Black holes- these are not holes in outer space, but objects (remnants of massive stars) with a very large mass and density. Black holes do not possess any supernatural or magical powers, they are not "monsters of the Universe". They just have such a strong gravitational field that no radiation (neither visible - light, nor invisible) can leave them. Therefore, black holes are not visible. However, they can be detected by their effect on the surrounding stars, nebulae. Black holes are a completely common phenomenon in the Universe and you should not be afraid of them. There may be a supermassive black hole at the center of our galaxy.

Radius (or diameter). The sizes of stars vary widely - from a few kilometers (neutron stars) to 2,000 solar diameters (supergiants). As a rule, the smaller the star, the higher its average density. In neutron stars, the density reaches 10 13 g / cm 3! A thimble of such a substance would weigh 10 million tons on Earth. But in supergiants, the density is less than the density of air near the surface of the Earth.

The diameters of some stars compared to the Sun:

Sirius and Altair are 1.7 times larger,

Vega is 2.5 times larger,

Regulus 3.5 times more

Arcturus is 26 times bigger

Polar is 30 times larger,

Rigel is 70 times larger,

Deneb is 200 times more

Antares is 800 times bigger

YV Canis Major is 2,000 times larger (the largest known star).

Luminosity is the total energy emitted by an object (in this case, stars) per unit of time. The luminosity of stars is usually compared with the luminosity of the Sun (the luminosity of stars is expressed in terms of the luminosity of the Sun). Sirius, for example, radiates 22 times more energy than the Sun (the luminosity of Sirius is 22 Suns). The luminosity of Vega is 50 Suns, and the luminosity of Deneb is 54,000 Suns (Deneb is one of the most powerful stars).

The apparent brightness (more correctly, brilliance) of a star in the earth's sky depends on:

- distance to the star. If a star approaches us, then its apparent brightness will gradually increase. Conversely, as a star moves away from us, its apparent brightness will gradually decrease. If we take two identical stars, then the one closest to us will seem brighter.

- on the temperature of the outer layers. The hotter the star, the more light energy it sends into space, and the brighter it will appear. If a star cools, then its apparent brightness in the sky will decrease. Two stars of the same size and at the same distance from us will appear the same in apparent brightness, provided that they emit the same amount of light energy, i.e. have the same temperature of the outer layers. If one of the stars is colder than the other, then it will appear less bright.

- size (diameter). If we take two stars with the same temperature of the outer layers (of the same color) and place them at the same distance from us, then the larger star will emit more light energy, which means it will appear brighter in the sky.

- from the absorption of light by clouds of cosmic dust and gas that are in the path of the line of sight. The thicker the layer of cosmic dust, the more light from the star it absorbs, and the dimmer the star appears. If we take two identical stars and place a gas-dust nebula in front of one of them, then just this star will appear less bright.

- from the height of the star above the horizon. There is always a dense haze near the horizon, which absorbs some of the light from the stars. Near the horizon (shortly after sunrise or shortly before sunset) the stars always appear dimmer than when they are overhead.

It is very important not to confuse the concepts of "appear" and "be". star may be very bright in itself, but seem dim due to various reasons: due to the large distance to it, due to its small size, due to the absorption of its light by cosmic dust or dust in the Earth's atmosphere. Therefore, when they talk about the brightness of a star in the earth's sky, they use the phrase "apparent brightness" or "brilliance".

As already mentioned, there are binary stars. But there are also triple (for example, α Centauri), and quadruple (for example, ε Lyra), and five, and six (for example, Castor), etc. The individual stars in a star system are called components. Stars with more than two components are called multiples stars. All components of a multiple star are connected by mutual gravitational forces (form a system of stars) and move along complex trajectories.

If there are many components, then this is no longer a multiple star, but star cluster. Distinguish ball And scattered star clusters. Globular clusters contain many old stars and are older than open clusters, which contain many young stars. Globular clusters are quite stable, because the stars in them are at small distances from each other and the forces of mutual attraction between them are much greater than between the stars of open clusters. Open clusters dissipate even more over time.

Open clusters, as it is correct, are located in the band of the Milky Way or nearby. On the contrary, globular clusters are located in the starry sky away from the Milky Way.

Some star clusters can be seen in the sky even with the naked eye. For example, open clusters of Hyades and Pleiades (M 45) in Taurus, open clusters of Manger (M 44) in Cancer, globular cluster M 13 in Hercules. Quite a lot of them can be seen with binoculars.

main sequence. Our star also belongs to this type -. From the point of view of stellar evolution, the main sequence is the place on the Hertzsprung-Russell diagram where the star spends most of its life.

Hertzsprung-Russell diagram.

The main sequence stars are divided into classes, which we will consider below:

Class O are blue stars, their temperature is 22,000 °C. Typical stars are Zeta in the constellation Puppis, 15 Unicorn.

Class B are white-blue stars. Their temperature is 14,000 °C. Their temperature is 14,000 °C. Typical stars: Epsilon in the constellation Orion, Rigel, Kolos.

Class A are white stars. Their temperature is 10,000 °C. Typical stars are Sirius, Vega, Altair.

Class F are white-yellow stars. Their surface temperature is 6700 °C. Typical stars Canopus, Procyon, Alpha in the constellation Perseus.

Class G are yellow stars. Temperature 5 500 °С. Typical stars: Sun (spectrum C-2), Capella, Alpha Centauri.

Class K are yellow-orange stars. Temperature 3 800 °C. Typical stars: Arthur, Pollux, Alpha Ursa Major.

Class M -. These are red stars. Temperature 1 800 °C. Typical stars: Betelgeuse, Antares

In addition to main sequence stars, astronomers distinguish the following types of stars:

A brown dwarf through the eyes of an artist.

Brown dwarfs are stars in which nuclear reactions could never compensate for energy losses due to radiation. Their spectral class is M - T and Y. Thermonuclear processes can occur in brown dwarfs, but their mass is still too small to start the reaction of converting hydrogen atoms into helium atoms, which is the main condition for the life of a full-fledged star. Brown dwarfs are rather "dim" objects, if that term can be applied to such bodies, and astronomers study them mainly due to the infrared radiation they give off.

Red giants and supergiants are stars with a rather low effective temperature of 2700-4700 ° C, but with a huge luminosity. Their spectrum is characterized by the presence of molecular absorption bands, and the emission maximum falls on the infrared range.

Wolf-Rayet type stars are a class of stars that are characterized by very high temperature and luminosity. Wolf-Rayet stars differ from other hot stars by the presence in the spectrum of broad emission bands of hydrogen, helium, as well as oxygen, carbon, and nitrogen in various degrees of ionization. The final clarity of the origin of Wolf-Rayet type stars has not been achieved. However, it can be argued that in our Galaxy these are the helium remnants of massive stars that shed a significant part of the mass at some stage of their evolution.

T Tauri stars are a class of variable stars named for their prototype T Tauri (final protostars). They can usually be found close to molecular clouds and identified by their (highly irregular) optical variability and chromospheric activity. They belong to the stars of spectral classes F, G, K, M and have a mass less than two solar. Their surface temperature is the same as that of main sequence stars of the same mass, but they have a slightly higher luminosity because their radius is larger. The main source of their energy is gravitational compression.

Bright blue variables, also known as S doradus variables, are very bright blue pulsating hypergiants named after the star S Doradus. They are extremely rare. The bright blue variables can shine a million times brighter than the Sun and have a mass of 150 solar masses, approaching the theoretical mass limit of a star, making them the brightest, hottest, and most powerful stars in the universe.

White dwarfs are a type of "dying" star. Small stars such as our Sun, which are widely distributed in the Universe, will turn into white dwarfs at the end of their lives - these are small stars (the former cores of stars) with a very high density, which is a million times higher than the density of water. The star is deprived of energy sources and gradually cools down, becoming dark and invisible, but the cooling process can last for billions of years.

Neutron stars - a class of stars, like white dwarfs, are formed after the death of a star with a mass of 8-10 solar masses (stars with a larger mass already form). In this case, the nucleus is compressed until most of the particles turn into neutrons. One of the features of neutron stars is a strong magnetic field. Thanks to it and the rapid rotation acquired by the star due to non-spherical collapse, radio and X-ray sources, called pulsars, are observed in space.

What color are the stars

Star colors. The stars have a variety of colors. Arcturus has a yellow-orange hue, Rigel is white-blue, Antares is bright red. The dominant color in the spectrum of a star depends on the temperature of its surface. The gas envelope of a star behaves almost like an ideal radiator (absolutely black body) and completely obeys the classical radiation laws of M. Planck (1858–1947), J. Stefan (1835–1893) and V. Wien (1864–1928), which relate body temperature and the nature of its radiation. Planck's law describes the distribution of energy in the spectrum of a body. He indicates that with increasing temperature, the total radiation flux increases, and the maximum in the spectrum shifts towards short waves. The wavelength (in centimeters) that accounts for the maximum radiation is determined by Wien's law: l max = 0.29/ T. It is this law that explains the red color of Antares ( T= 3500 K) and Rigel's bluish color ( T= 18000 K). Stefan's law gives the total radiant flux at all wavelengths (in watts per square meter): E = 5,67" 10 –8 T 4 .

Spectra of stars. The study of stellar spectra is the foundation of modern astrophysics. The spectrum can be used to determine the chemical composition, temperature, pressure and velocity of gas in the star's atmosphere. The Doppler shift of the lines is used to measure the speed of the star itself, for example, along the orbit in a binary system.

In the spectra of most stars, absorption lines are visible; narrow gaps in the continuous distribution of radiation. They are also called Fraunhofer or absorption lines. They are formed in the spectrum because the radiation from the hot lower layers of the star's atmosphere, passing through the colder upper layers, is absorbed at certain wavelengths characteristic of certain atoms and molecules.

The absorption spectra of stars vary greatly; however, the intensity of the lines of any chemical element does not always reflect its true amount in the stellar atmosphere: to a much greater extent, the shape of the spectrum depends on the temperature of the stellar surface. For example, iron atoms are found in the atmosphere of most stars. However, the lines of neutral iron are absent in the spectra of hot stars, since all the iron atoms there are ionized. Hydrogen is the main component of all stars. But the optical lines of hydrogen are not visible in the spectra of cold stars, where it is underexcited, and in the spectra of very hot stars, where it is fully ionized. But in the spectra of moderately hot stars with a surface temperature of approx. At 10,000 K, the most powerful absorption lines are the lines of the Balmer series of hydrogen, which are formed during the transitions of atoms from the second energy level.

The gas pressure in the star's atmosphere also has some effect on the spectrum. At the same temperature, the lines of ionized atoms are stronger in low-pressure atmospheres, because there these atoms are less likely to capture electrons and therefore live longer. Atmospheric pressure is closely related to the size and mass, and hence to the luminosity of a star of a given spectral class. Having established the pressure from the spectrum, it is possible to calculate the luminosity of the star and, comparing it with the visible brightness, determine the "distance modulus" ( M- m) and the linear distance to the star. This very useful method is called the method of spectral parallaxes.

Color index. The spectrum of a star and its temperature are closely related to the color index, i.e. with the ratio of the brightness of the star in the yellow and blue ranges of the spectrum. Planck's law, which describes the distribution of energy in the spectrum, gives an expression for the color index: C.I. = 7200/ T- 0.64. Cold stars have a higher color index than hot ones, i.e. cool stars are relatively brighter in yellow than in blue. Hot (blue) stars appear brighter on conventional photographic plates, while cool stars appear brighter to the eye and special photographic emulsions that are sensitive to yellow rays.

Spectral classification. All the variety of stellar spectra can be put into a logical system. The Harvard spectral classification was first introduced in Henry Draper's catalog of stellar spectra, prepared under the guidance of E. Pickering (1846–1919). First, the spectra were sorted by line intensities and labeled with letters in alphabetical order. But the physical theory of spectra developed later made it possible to arrange them in a temperature sequence. The letter designation of the spectra has not been changed, and now the order of the main spectral classes from hot to cold stars looks like this: O B A F G K M. Additional classes R, N and S denote spectra similar to K and M, but with a different chemical composition. Between each two classes, subclasses are introduced, indicated by numbers from 0 to 9. For example, the spectrum of type A5 is in the middle between A0 and F0. Additional letters sometimes mark the features of stars: “d” is a dwarf, “D” is a white dwarf, “p” is a peculiar (unusual) spectrum.

The most accurate spectral classification is the MK system created by W. Morgan and F. Keenan at the Yerkes Observatory. This is a two-dimensional system in which the spectra are arranged both by temperature and by the luminosity of stars. Its continuity with the one-dimensional Harvard classification is that the temperature sequence is expressed by the same letters and numbers (A3, K5, G2, etc.). But additional luminosity classes are introduced, marked with Roman numerals: Ia, Ib, II, III, IV, V and VI, respectively, indicating bright supergiants, supergiants, bright giants, normal giants, subgiants, dwarfs (main sequence stars) and subdwarfs. For example, the designation G2 V refers to a star like the Sun, while the designation G2 III indicates that it is a normal giant with a temperature about the same as that of the Sun.

> Stars

Stars- massive gas balls: history of observations, names in the Universe, classification with photos, birth of a star, development, double stars, list of the brightest.

Stars- celestial bodies and giant luminous spheres of plasma. There are billions of them in our Milky Way galaxy alone, including the Sun. Not so long ago, we learned that some of them also have planets.

History of stellar observations

Now you can easily buy a telescope and observe the night sky or use telescopes online on our website. Since ancient times, the stars in the sky have played an important role in many cultures. They were noted not only in myths and religious stories, but also served as the first navigational tools. That is why astronomy is considered one of the oldest sciences. The advent of telescopes and the discovery of the laws of motion and gravity in the 17th century helped to understand that all stars resemble ours, which means they obey the same physical laws.

The invention of photography and spectroscopy in the 19th century (the study of the wavelengths of light emanating from objects) made it possible to penetrate into the stellar composition and principles of motion (the creation of astrophysics). The first radio telescope appeared in 1937. With its help, it was possible to find invisible stellar radiation. And in 1990, the first Hubble Space Telescope was launched, capable of obtaining the deepest and most detailed view of the Universe (high-quality Hubble photos of various celestial bodies can be found on our website).

The name of the stars of the universe

Ancient people did not have our technical advantages, so they recognized the images of various creatures in celestial objects. These were the constellations about which myths were composed in order to remember the names. Moreover, almost all of these names have been preserved and are used today.

In the modern world, there are (among them 12 belong to the zodiac). The brightest star is labeled alpha, the second brightest is beta, and the third is gamma. And so it goes until the end of the Greek alphabet. There are stars that represent parts of the body. For example, the brightest star of Orion (Alpha Orion) is "the arm (armpit) of a giant."

Do not forget that all this time a lot of catalogs were compiled, whose designations are still used. For example, the Henry Draper Catalog offers a spectral classification and positions for 272,150 stars. The Betelgeuse designation is HD 39801.

But there are an incredibly large number of stars in the sky, so for new ones they use abbreviations denoting a stellar type or catalog. For example, PSR J1302-6350 is a pulsar (PSR), J is using the "J2000" coordinate system, and the last two groups of digits are coordinates with latitude and longitude codes.

Are the stars all the same? Well, when viewed without the use of technology, they are only slightly different in brightness. But these are just huge balls of gas, right? Not really. In fact, stars have a classification based on their main characteristics.

Among the representatives you can meet blue giants and tiny brown dwarfs. Sometimes there are bizarre stars, like neutron ones. Diving into the Universe is impossible without understanding these things, so let's get to know the stellar types better.

Most of the stars in the universe are in the main sequence. You can remember the Sun, Alpha Centauri A and Sirus. They can radically differ in scale, massiveness and brightness, but they perform one process: they transform hydrogen into helium. This produces a huge energy surge. Such a star experiences a sensation of hydrostatic balance. Gravity causes an object to shrink, but nuclear fusion pushes it out. These forces work in balance, and the star manages to maintain the shape of a sphere. The size depends on the massiveness. The line is 80 Jupiter masses. This is the minimum mark at which it is possible to activate the melting process. But in theory, the maximum mass is 100 solar.

If there is no fuel, then the star no longer has enough mass to continue nuclear fusion. She turns into a white dwarf. External pressure does not work, and it shrinks in size due to gravity. The dwarf continues to shine because there are still hot temperatures. When it cools down, it will reach the background temperature. It will take hundreds of billions of years, so it is simply impossible to find a single representative yet. Planetary systems of white dwarfs Astrophysicist Roman Rafikov on disks around white dwarfs, Saturn's rings and the future of the solar system compact stars Astrophysicist Alexander Potekhin on white dwarfs, the density paradox and neutron stars:

Cepheids are stars that have evolved from the main sequence to the Cepheid instability strip. These are ordinary radio-pulsating stars with a noticeable relationship between periodicity and luminosity. Scientists value them for this, because they are excellent assistants in determining distances in space. They also show radial velocity variations corresponding to the photometric curves. The brighter ones have a long periodicity. Classical representatives are supergiants, whose mass is 2-3 times greater than the solar one. They are in the moment of burning fuel at the stage of the main sequence and transform into red giants, crossing the Cepheid instability line.

To be more precise, the concept of "double star" does not reflect the real picture. In fact, we have a star system in front of us, represented by two stars making revolutions around a common center of mass. Many people make the mistake of mistaking two objects for a double star that appear to be close to each other when viewed with the naked eye. Scientists benefit from these objects because they help calculate the mass of individual participants. When they move in a common orbit, Newton's calculations for gravity allow mass to be calculated with incredible accuracy. Several categories can be distinguished according to visual properties: occult, visual binary, spectroscopic binary, and astrometric. Occulting - stars whose orbits create a horizontal line from the point of observation. That is, a person sees a double eclipse on the same plane (Algol). Visual - two stars that can be resolved with a telescope. If one of them shines very brightly, it can be difficult to separate the other.

star formation

Let's take a closer look at the process of star birth. First we see a giant slowly rotating cloud filled with hydrogen and helium. Internal gravity causes it to curl inwards, causing it to spin faster. The outer parts are transformed into a disk, and the inner parts into a spherical cluster. The material breaks down, becoming hotter and denser. Soon a spherical proto-star appears. When heat and pressure rise to 1 million °C, the atomic nuclei fuse and a new star ignites. Nuclear fusion converts a small amount of atomic mass into energy (1 gram of mass converted into energy is equivalent to the explosion of 22,000 tons of TNT). See also the explanation on the video to better understand the issue of stellar origin and development.

Evolution of protostellar clouds

Astronomer Dmitry Wiebe on actualism, molecular clouds and star birth:

The birth of the stars

Astronomer Dmitry Wiebe on protostars, the discovery of spectroscopy and the gravoturbulent model of star formation:

Flares on young stars

Astronomer Dmitry Wiebe on supernovae, types of young stars and a flash in the constellation Orion:

Star evolution

Based on the mass of a star, one can determine its entire evolutionary path, since it goes through certain template stages. There are stars of intermediate mass (like the Sun) 1.5-8 times the solar mass, more than 8, and also up to half the solar mass. Interestingly, the greater the mass of a star, the shorter its lifespan. If it reaches less than a tenth of the sun, then such objects fall into the category of brown dwarfs (they cannot ignite nuclear fusion).

An intermediate-mass object begins life as a cloud 100,000 light-years across. To collapse into a protostar, the temperature must be 3725°C. From the moment the hydrogen fusion begins, T Tauri can form - a variable with fluctuations in brightness. The subsequent process of destruction will take 10 million years. Further, its expansion will be balanced by the compression of gravity, and it will appear as a main sequence star, receiving energy from hydrogen fusion in the core. The bottom figure shows all the stages and transformations in the evolution of stars.

When all the hydrogen is melted into helium, gravity will crush the matter into the core, which will start a rapid process of heating. The outer layers expand and cool, and the star becomes a red giant. Next, helium begins to fuse. When it also dries up, the core contracts and becomes hotter, expanding the shell. At maximum temperature, the outer layers are blown away, leaving a white dwarf (carbon and oxygen) whose temperature reaches 100,000 °C. There is no more fuel, so there is a gradual cooling. Billions of years later, they end their lives as black dwarfs.

The processes of formation and death in a star with a high mass occur incredibly quickly. It only takes 10,000-100,000 years for it to pass from a protostar. During the main sequence period, these are hot and blue objects (from 1000 to a million times brighter than the Sun and 10 times wider). Next, we see a red supergiant begin to fuse carbon into heavier elements (10,000 years). The result is an iron core with a width of 6000 km, whose nuclear radiation can no longer resist the force of gravity.

As a star approaches 1.4 solar masses, the electron pressure can no longer keep the core from collapsing. Because of this, a supernova is formed. Upon destruction, the temperature rises to 10 billion °C, breaking the iron into neutrons and neutrinos. In just a second, the core shrinks to a width of 10 km and then explodes in a Type II supernova.

If the remaining core reached less than 3 solar masses, then it turns into a neutron star (practically from neutrons alone). If it rotates and emits radio pulses, then it is. If the core is more than 3 solar masses, then nothing will keep it from destruction and transformation into.

A low-mass star uses up its fuel reserves so slowly that it won't become a main-sequence star until 100 billion to 1 trillion years from now. But the age of the Universe reaches 13.7 billion years, which means that such stars have not yet died. Scientists have found that these red dwarfs are not destined to merge with anything but hydrogen, which means they will never grow into red giants. As a result, their fate is cooling and transformation into black dwarfs.

Thermonuclear reactions and compact objects

Astrophysicist Valery Suleimanov on atmospheric modeling, the "big controversy" in astronomy, and neutron star mergers:

Astrophysicist Sergei Popov on the distance to stars, the formation of black holes and the Olbers paradox:

We are accustomed to our system being illuminated exclusively by one star. But there are other systems in which two stars in the sky orbit relative to each other. To be more precise, only 1/3 of the stars similar to the Sun are located alone, and 2/3 are double stars. For example, Proxima Centauri is part of a multiple system that includes Alpha Centauri A and B. Approximately 30% of the stars are multiple.

This type is formed when two protostars develop side by side. One of them will be stronger and will begin to influence gravity, creating mass transfer. If one appears in the form of a giant, and the second is a neutron star or a black hole, then we can expect the appearance of an X-ray binary system, where the substance is incredibly hot - 555500 ° C. In the presence of a white dwarf, gas from a companion can flare up as a nova. Periodically, the dwarf's gas builds up and is able to instantly merge, causing the star to explode in a Type I supernova that can outshine the galaxy with its brilliance for several months.

Relativistic double stars

Astrophysicist Sergei Popov on measuring the mass of a star, black holes and ultra-powerful sources:

Properties of double stars

Astrophysicist Sergei Popov on planetary nebulae, white helium dwarfs and gravitational waves:

Characteristics of the stars

Brightness

To describe the brightness of stellar celestial bodies, magnitude and luminosity are used. The concept of magnitude is based on the work of Hipparchus in 125 BC. He numbered the star groups based on apparent brightness. The brightest are the first magnitude, and so on up to the sixth. However, the distance between and a star can affect visible light, so now they add a description of the actual brightness - an absolute value. It is calculated using the apparent magnitude, as if it were 32.6 light-years from Earth. The modern magnitude scale rises above six and falls below one (the apparent magnitude reaches -1.46). Below you can study the list of the brightest stars in the sky from the position of an observer of the Earth.

List of brightest stars visible from Earth

Other famous stars:

The luminosity of a star is the rate at which energy is emitted. It is measured by comparison with solar brightness. For example, Alpha Centauri A is 1.3 times brighter than the Sun. To make the same calculations in absolute terms, you have to take into account that 5 on the absolute scale is equal to 100 on the luminosity mark. Brightness depends on temperature and size.

Color

You may have noticed that the stars differ in color, which actually depends on the surface temperature.

Each star has one color, but produces a wide spectrum, including all types of radiation. A variety of elements and compounds absorb and emit colors or wavelengths of color. Studying the stellar spectrum, you can understand the composition.