Walter Scott is a black dwarf. Neutron stars What is a black dwarf

Big and small, hot and cold, charged and uncharged. In this article we will give a classification of the main types of stars.

One of the classifications of stars is spectral classification. According to this classification, stars are assigned to one class or another according to their spectrum. The spectral classification of stars serves many problems in stellar astronomy and astrophysics. A qualitative description of the observed spectrum makes it possible to estimate important astrophysical characteristics of a star, such as its effective surface temperature, luminosity, and, in some cases, features of its chemical composition.

Some stars do not fall into any of the listed spectra. Such stars are called peculiar. Their spectra do not fit into the O–B–A–F–G–K–M temperature sequence. Although often such stars represent certain evolutionary stages of completely normal stars, or represent stars that are not quite characteristic of the immediate vicinity (stars poor in metals, such as stars of globular clusters and halo). In particular, stars with peculiar spectra include stars with different features of the chemical composition, which manifests itself in the strengthening or weakening of the spectral lines of some elements.

Hertzsprung-Russell diagram

A good understanding of the classification of stars allows Hertzsprung-Russell diagram. It shows the relationship between absolute magnitude, luminosity, spectral type, and surface temperature of a star. Unexpected is the fact that the stars in this diagram are not arranged randomly, but form well-defined areas. The diagram was proposed in 1910 independently by the researchers E. Hertzsprung and G. Russell. It is used to classify stars and corresponds to modern ideas about.

Most of the stars are located on the so-called main sequence. The existence of the main sequence is due to the fact that the stage of hydrogen burning is ~90% of the evolutionary time of most stars: the burning of hydrogen in the central regions of the star leads to the formation of an isothermal helium core, the transition to the red giant stage, and the departure of the star from the main sequence. The relatively short evolution of red giants leads, depending on their mass, to the formation of white dwarfs, neutron stars or.

yellow dwarf

Being at different stages of their evolutionary development, stars are divided into normal stars, dwarf stars, giant stars. Normal stars are the main sequence stars. One such example is our Sun. Sometimes such normal stars are called yellow dwarfs.

The star may be called red giant at the time of star formation and in the later stages of development. At an early stage of development, a star radiates gravitational energy released during compression until the compression is stopped by the onset of a thermonuclear reaction. At the later stages of the evolution of stars, after the hydrogen burns out in their interiors, the stars descend from the main sequence and move to the region of red giants and supergiants of the Hertzsprung-Russell diagram: this stage lasts ~ 10% of the time of the "active" life of stars, that is, the stages of their evolution , during which nucleosynthesis reactions take place in the stellar interior.

giant stars

giant star has a relatively low surface temperature, about 5000 degrees. A huge radius, reaching 800 solar radii, and due to such large sizes, a huge luminosity. The maximum radiation falls on the red and infrared region of the spectrum, which is why they are called red giants.

dwarf stars are the opposite of giants and include several different subspecies:

• white dwarf- evolved stars with a mass not exceeding 1.4 solar masses, deprived of their own sources of thermonuclear energy. The diameter of such stars can be hundreds of times smaller than the sun, and therefore the density can be 1,000,000 times that of water.
• red dwarf- a small and relatively cool main sequence star with a spectral type M or upper K. They are quite different from other stars. The diameter and mass of red dwarfs does not exceed a third of the solar mass (the lower mass limit is 0.08 solar, followed by brown dwarfs).
• brown dwarf- substellar objects with masses in the range of 5-75 Jupiter masses (and a diameter approximately equal to the diameter of Jupiter), in the depths of which, unlike main-sequence stars, there is no thermonuclear fusion reaction with the conversion of hydrogen into helium.
• Subbrown dwarfs or brown subdwarfs- cold formations, in terms of mass, lying below the limit of brown dwarfs. They are mostly considered.
• black dwarf are white dwarfs that have cooled down and therefore do not radiate in the visible range. Represents the final stage in the evolution of white dwarfs. The masses of black dwarfs, like the masses of white dwarfs, are limited from above by 1.4 solar masses.

In addition to those listed above, there are several other products of stellar evolution:

• neutron star. Star formations with masses on the order of 1.5 solar masses and sizes noticeably smaller than white dwarfs, on the order of 10-20 km in diameter. The density of such stars can reach 1,000,000,000,000 of the densities of water. And the magnetic field is the same number of times greater than the magnetic field of the earth. Such stars consist mainly of neutrons tightly compressed by gravitational forces. Often such stars are.
• New star. Stars that suddenly increase in luminosity by a factor of 10,000. A nova is a binary system consisting of a white dwarf and a main sequence companion star. In such systems, gas from the star gradually flows into the white dwarf and periodically explodes there, causing a burst of luminosity.
• Supernova is a star ending its evolution in a catastrophic explosive process. The flare in this case can be several orders of magnitude greater than in the case of a new star. Such a powerful explosion is a consequence of the processes taking place in the star at the last stage of evolution.
• double star are two gravitationally bound stars revolving around a common center of mass. Sometimes there are systems of three or more stars, in such a general case the system is called a multiple star. In cases where such a star system is not too far removed from the Earth, in

The largest of Thanos' generals, Black Dwarf seems to be the more common (in terms of strength) of Thanos' generals, as his special abilities are only super strength and impenetrable skin. As a weapon, the Black Dwarf sometimes carries a huge (almost his size) mace.

While searching for his son, Thane, Thanos sent his generals to the Illuminati. The Black Dwarf went to Wakanda, where he received a good rebuff from the Black Punters: T "challa and Shuri.

After the loss, the Black Dwarf begged for mercy from Thanos, but the mad titan smashed his face into the floor.

After defeating the builders, the Avengers set off to liberate the Earth. Thanos left the Black Dwarf on Titan, where part of the team of earthly heroes and the Intergalactic Council went in the person of Kl "rt - Superskrull, Ronan - the Accuser, Gladiator and Annihilus. The Black Dwarf expected to defeat them in order to win the respect of Thanos again. Before the battle, the Black Dwarf kills one of his soldiers for mentioning his shame in Wakanda.

When the heroes arrived, the Black Dwarf scattered most of the Avengers, with the exception of Shang-Chi, who was ready to fight the general alone. The villain was impressed by the bravery of the kung fu master when a dialogue began between them:

Black Dwarf: - Why are you still on your feet?

Shang-Chi: - Falls... Does a tree fall... from the wind?

Black Dwarf: - Hmph! You're dying beautifully, man. But death is death, isn't it? Goodbye.

But at that moment, an intergalactic council arrives, and the gladiator saves Shang-Chi by attacking the Black Dwarf and destroying his mace. A skirmish ensues between Thanos' general and the intergalactic council. As a result, Ronan, shouting that it was time to condemn the Black Dwarf, crushed his skull, thereby killing him.

7. Black dwarfs

black dwarfs- last stage of evolution white dwarf, at which it ceases to radiate in the visible range. Currently, black dwarfs are classified as white dwarfs, but with the caveat that this is the final stage of his life. In order to understand what is black dwarf need to understand the concept white dwarf.

What is a white dwarf and what is its nature?

Let's take our The sun. During a thermonuclear reaction on the Sun, hydrogen turns into helium, the star slowly expands, becoming heavier. Over time, when there will be even less hydrogen and more helium, even heavier elements, such as carbon, oxygen, and iron, will be synthesized from the latter. The sun will swell, turning into red giant. Its outer layers will be far beyond the Earth's orbit.

When the star's mass becomes critical, it will explode in a supernova, "thrown off" the outer layers. At the same time, the mass of our Sun will not be enough to form a black hole or become a neutron star. After the explosion, the Sun will become white dwarf.

Having dropped part of the mass, the star becomes unable to continue the process of generation of thermonuclear energy. Now white dwarf cools down slowly, gradually turning into a discharge black dwarfs. At the same time, the star is very stable and will be in this state for a very long time.

white dwarfs (and black dwarfs, including) may differ in their composition, luminosity, mass and other parameters, but in general they are all stars, the mass of which is comparable to the mass of the Sun or a little more, and their diameter is tens of times smaller than the solar one. The light of such stars is much dimmer than it was before.

closest to Earth is a white dwarf van maanen star, which is located 14.4 light years in the constellation Pisces. And perhaps the most famous white dwarf is the star Sirius B, which is one of the stars Sirius star system. Star mass Sirius B approximately equal to the Sun, this makes the star one of the largest stars among white dwarfs.

There are many different stars in the universe. Big and small, hot and cold, charged and uncharged. In this article, we will name the main types of stars, as well as give a detailed description of the Yellow and White dwarfs.

1. yellow dwarf. A yellow dwarf is a type of small main sequence star with a mass of 0.8 to 1.2 solar masses and a surface temperature of 5000–6000 K. See below for more on this type of star.
2. red giant. A red giant is a large reddish or orange star. The formation of such stars is possible both at the stage of star formation and at the later stages of their existence. The largest of the giants turn into red supergiants. A star called Betelgeuse in the constellation Orion is the most striking example of a red supergiant.
3. white dwarf. A white dwarf is what remains of an ordinary star with a mass not exceeding 1.4 solar masses after it passes through the red giant stage. See below for more details on this type of star.
4. red dwarf. Red dwarfs are the most common stellar-type objects in the universe. Estimates of their abundance range from 70 to 90% of the number of all stars in the galaxy. They are quite different from other stars.
5. brown dwarf. Brown dwarf - substellar objects (with masses in the range of approximately 0.01 to 0.08 solar masses, or, respectively, from 12.57 to 80.35 Jupiter masses and a diameter approximately equal to that of Jupiter), in the depths of which, in contrast from main sequence stars, there is no thermonuclear fusion reaction with the conversion of hydrogen into helium.
6. subbrown dwarfs. Subbrown dwarfs or brown subdwarfs are cold formations that lie below the brown dwarf limit in mass. Their mass is less than about one hundredth of the mass of the Sun or, respectively, 12.57 masses of Jupiter, the lower limit is not defined. They are more commonly considered planets, although the scientific community has not yet come to a final conclusion about what is considered a planet and what is a subbrown dwarf.
7. black dwarf. Black dwarfs are white dwarfs that have cooled down and therefore do not radiate in the visible range. Represents the final stage in the evolution of white dwarfs. The masses of black dwarfs, like the masses of white dwarfs, are limited from above by 1.4 solar masses.
8. double star. A binary star is two gravitationally bound stars revolving around a common center of mass.
9. New star. Stars that suddenly increase in luminosity by a factor of 10,000. A nova is a binary system consisting of a white dwarf and a main sequence companion star. In such systems, gas from the star gradually flows into the white dwarf and periodically explodes there, causing a burst of luminosity.
10. Supernova. A supernova is a star that ends its evolution in a catastrophic explosive process. The flare in this case can be several orders of magnitude greater than in the case of a new star. Such a powerful explosion is a consequence of the processes taking place in the star at the last stage of evolution.
11. neutron star. Neutron stars (NS) are stellar formations with masses on the order of 1.5 solar masses and sizes noticeably smaller than white dwarfs, on the order of 10-20 km in diameter. They consist mainly of neutral subatomic particles - neutrons, tightly compressed by gravitational forces. In our Galaxy, according to scientists, there can be from 100 million to 1 billion neutron stars, that is, somewhere around one in a thousand ordinary stars.
12. Pulsars. Pulsars are cosmic sources of electromagnetic radiation coming to Earth in the form of periodic bursts (pulses). According to the dominant astrophysical model, pulsars are rotating neutron stars with a magnetic field that is tilted to the axis of rotation. When the Earth falls into the cone formed by this radiation, it is possible to record a radiation pulse that repeats at intervals equal to the period of revolution of the star. Some neutron stars make up to 600 revolutions per second.
13. cepheid. Cepheids are a class of pulsating variable stars with a fairly accurate period-luminosity relationship, named after the star Delta Cephei. One of the most famous Cepheids is the North Star. The above list of the main types (types) of stars with their brief characteristics, of course, does not exhaust the entire possible variety of stars in the Universe.

yellow dwarf

Being at different stages of their evolutionary development, stars are divided into normal stars, dwarf stars, giant stars. Normal stars are the main sequence stars. One such example is our Sun. Sometimes such normal stars are called yellow dwarfs.

Characteristic

Today we will briefly talk about yellow dwarfs, which are also called yellow stars. Yellow dwarfs are, as a rule, stars of average mass, luminosity and surface temperature. They are main-sequence stars, lying roughly in the middle of the Hertzsprung–Russell diagram and following cooler, less massive red dwarfs.

According to the Morgan-Keenan spectral classification, yellow dwarfs correspond mainly to the G luminosity class, but in transitional variations they sometimes correspond to the K class (orange dwarfs) or the F class in the case of yellow-white dwarfs.

The mass of yellow dwarfs is often in the range from 0.8 to 1.2 solar masses. At the same time, the temperature of their surface is for the most part from 5 to 6 thousand degrees Kelvin.

The brightest and most known representative of the yellow dwarfs is our Sun.

In addition to the Sun, among the yellow dwarfs closest to the Earth, it is worth noting:

1. Two components in the Alpha Centauri triple system, among which Alpha Centauri A is similar in luminosity spectrum to the Sun, and Alpha Centauri B is a typical K-class orange dwarf. The distance to both components is just over 4 light years.
2. The orange dwarf is the star Ran, also known as Epsilon Eridani, with a luminosity class of K. Astronomers estimated the distance to Ran at about 10 and a half light years.
3. The binary star 61 Cygni is just over 11 light-years from Earth. Both components of 61 Cygnus are typical K-class orange dwarfs.
4. Sun-like star Tau Ceti, about 12 light-years away from Earth, with a G luminosity spectrum and an interesting planetary system consisting of at least 5 exoplanets.

Education

The evolution of yellow dwarfs is very interesting. The lifespan of a yellow dwarf is approximately 10 billion years.

Like most stars, intense thermonuclear reactions take place in their interiors, in which mainly hydrogen burns out into helium. After the start of reactions involving helium in the core of the star, hydrogen reactions move more and more towards the surface. This becomes the starting point in the transformation of a yellow dwarf into a red giant. The result of such a transformation may be the red giant Aldebaran.

Over time, the surface of the star will gradually cool down, and the outer layers will begin to expand. At the final stages of evolution, the red giant sheds its shell, which forms a planetary nebula, and its core will turn into a white dwarf, which will further shrink and cool.

A similar future awaits our Sun, which is now in the middle stage of its development. After about 4 billion years, it will begin its transformation into a red giant, the photosphere of which, when expanding, can absorb not only the Earth and Mars, but even Jupiter.

The lifetime of a yellow dwarf is on average 10 billion years. After the entire supply of hydrogen burns out, the star increases many times in size and turns into a red giant. most planetary nebulae, and the core collapses into a small, dense white dwarf.

white dwarfs

White dwarfs are stars that have a large mass (of the order of the sun) and a small radius (radius of the Earth), which is less than the Chandrasekhar limit for the selected mass, which are the product of the evolution of red giants. The process of production of thermonuclear energy in them is stopped, which leads to the special properties of these stars. According to various estimates, their number in our Galaxy ranges from 3 to 10% of the total stellar population.

Discovery history

In 1844, the German astronomer and mathematician Friedrich Bessel, when observing Sirius, discovered a slight deviation of the star from rectilinear motion, and made an assumption that Sirius had an invisible massive satellite star.

His assumption was confirmed already in 1862, when the American astronomer and telescope designer Alvan Graham Clark, while adjusting the largest refractor at that time, discovered a dim star near Sirius, which was later dubbed Sirius B.

The white dwarf Sirius B has a low luminosity, and the gravitational field affects its bright companion quite noticeably, which indicates that this star has an extremely small radius with a significant mass. Thus, for the first time, a type of object called white dwarfs was discovered. The second such object was the star Maanen, located in the constellation Pisces.

How are white dwarfs formed?

After all the hydrogen in an aging star burns out, its core contracts and heats up, which contributes to the expansion of its outer layers. The effective temperature of the star drops, and it turns into a red giant. The rarefied shell of the star, very weakly connected with the core, eventually dissipates in space, flowing to neighboring planets, and a very compact star, called a white dwarf, remains in place of the red giant.

For a long time it remained a mystery why white dwarfs, which have a temperature exceeding the temperature of the Sun, are small compared to the size of the Sun, until it became clear that the density of the matter inside them is extremely high (within 10 5 - 10 9 g / cm 3). There is no standard dependence - mass-luminosity - for white dwarfs, which distinguishes them from other stars. A huge amount of matter is “packed” in an extremely small volume, which is why the density of a white dwarf is almost 100 times that of water.

The temperature of white dwarfs remains almost constant, despite the absence of thermonuclear reactions inside them. What explains this? Due to the strong compression, the electron shells of the atoms begin to penetrate each other. This continues until the distance between the nuclei becomes minimal, equal to the radius of the smallest electron shell.

As a result of ionization, electrons begin to move freely relative to the nuclei, and the matter inside the white dwarf acquires physical properties that are characteristic of metals. In such matter, energy is transferred to the surface of the star by electrons, the speed of which increases more and more as it contracts: some of them move at a speed corresponding to a temperature of a million degrees. The temperature on the surface and inside the white dwarf can differ dramatically, which does not lead to a change in the diameter of the star. Here you can make a comparison with a cannonball - cooling down, it does not decrease in volume.

The white dwarf fades extremely slowly: over hundreds of millions of years, the radiation intensity drops by only 1%. But in the end, it will have to disappear, turning into a black dwarf, which may take trillions of years. White dwarfs can be called unique objects of the Universe. No one has yet succeeded in reproducing the conditions in which they exist in earthly laboratories.

X-ray emission from white dwarfs

The surface temperature of young white dwarfs, isotropic stellar cores after shell ejection, is very high - more than 2 10 5 K, however, it drops quite quickly due to radiation from the surface. Such very young white dwarfs are observed in the X-ray range (for example, observations of the white dwarf HZ 43 by the ROSAT satellite). In the X-ray range, the luminosity of white dwarfs exceeds the luminosity of main-sequence stars: the images of Sirius taken by the Chandra X-ray telescope can serve as an illustration - on them, the white dwarf Sirius B looks brighter than Sirius A of spectral class A1, which in the optical range is ~ 10,000 times brighter than Sirius B.

The surface temperature of the hottest white dwarfs is 7 10 4 K, the coldest is less than 4 10 3 K.

A feature of the radiation of white dwarfs in the X-ray range is the fact that the main source of X-ray radiation for them is the photosphere, which sharply distinguishes them from "normal" stars: in the latter, the crown emits X-rays, heated to several million kelvins, and the temperature of the photosphere is too low for emission of x-rays.

In the absence of accretion, the source of luminosity of white dwarfs is the supply of thermal energy of ions in their interiors; therefore, their luminosity depends on age. The quantitative theory of the cooling of white dwarfs was built in the late 1940s by Professor Samuil Kaplan.

A black dwarf is a white dwarf that has cooled down to the temperature of the cosmic microwave background, and therefore has become invisible. Unlike red dwarfs, brown dwarfs, and white dwarfs, black dwarfs are hypothetical objects in the universe.

When a star evolved into a white dwarf, it no longer had a source of heat and shone just because it was still hot. Like something was taken out of the oven. If left alone, a white dwarf will eventually cool down to the temperature of its environment. Unlike today's dinner, which cools down through convection, conduction, and radiation, a white dwarf cools only through radiation.

Since the pressure of electron degeneracy stops it from collapsing, which will lead to , the white dwarf is a fantastic conductor of heat (Fermi gas physics explains the conductivity of both white dwarfs and metals!). How quickly a white dwarf will cool is easy to calculate... it just depends on the initial temperature, mass, and composition (most of them are carbon and oxygen; some are predominantly oxygen, neon, and magnesium; others are helium). And at least part of the core of the white dwarf can crystallize, the cooling curve will have a small bump in this place.

Not a black dwarf... not yet. White dwarf Sirius B.

The universe is only about 13.7 billion years old, so even a white dwarf formed 13 billion years ago (which is unlikely; it took a billion years or so to become white dwarfs) would still have a temperature of several thousand degrees. The coldest white dwarf observed to date has a temperature of just under 3000 Kelvin. He has a long way to go before he becomes a black dwarf.

It turns out that it is quite difficult to answer the question of how long it will take for a white dwarf to cool down to the temperature of the cosmic microwave background radiation. Why? Because there are many interesting effects that could be important, the consequences of these effects have not yet been modeled by scientists. For example, a white dwarf will contain little, and some of it may decay at intervals of quadrillions of years, generating heat. Matter is also not eternal, protons can also decay, generating heat. And the CMB gets colder with time because .

In any case, if we say, conventionally, that a white dwarf with a temperature of 5 Kelvin becomes a black dwarf, then it will take at least 10 15 years for it to become a black dwarf.

One more thing, there are no single white dwarfs; some have companions, forming together, for example, others can wander in a gas and dust cloud ... the falling mass also generates heat, and if enough hydrogen accumulates on the surface, then this star can explode like a hydrogen bomb (this is called), warming up the white a little dwarf.

The title of the article you read "Star black dwarf".