White stars: names, description, characteristics

If you look closely at the night sky, it's easy to see that the stars that look at us differ in color. Bluish, white, red, they shine smoothly or flicker, like a Christmas tree garland. In the telescope, the differences in color become more obvious. The reason that led to such a variety lies in the temperature of the photosphere. And, contrary to the logical assumption, the hottest are not red, but blue, white-blue and white stars. But first things first.

Spectral classification

Stars are huge red-hot balls made up of gas. The way we see them from the Earth depends on many parameters. For example, the stars do not really flicker. It is very easy to make sure of this: it is enough to remember the Sun. The effect of flickering arises from the fact that the light coming from cosmic bodies to us overcomes the interstellar medium, full of dust and gas. Another thing is color. It is a consequence of the heating of the shells (especially the photosphere) to certain temperatures. The true color may differ from the visible, but the difference is usually small.

Today, throughout the world, the Harvard spectral classification of stars is used. It is temperature and is based on the form and relative intensity of the spectral lines. To each class there correspond stars of a certain color. The classification was developed at the Harvard Observatory in 1890-1924.

One Briton Englishman Finiki Chewed Like Carrots

The main spectral classes are seven: O-B-A-F-G-K-M. This sequence reflects a gradual decrease in temperature (from O to M). To memorize it, there are special mnemonic formulas. In Russian one of them sounds like: "One Briton Englishman Finiki Chewed Like Carrots". To these classes are added two more. Letters C and S denote cold luminaries with bands of metal oxides in the spectrum. Consider star classes in more detail:

• Class O is characterized by the highest surface temperature (from 30 to 60 thousand Kelvin). Stars of this type exceed the Sun by mass in 60, and radially by 15 times. Their visible color is blue. By luminosity, they are ahead of our star more than a million times. The blue star HD93129A, belonging to this class, is characterized by one of the highest luminosity indicators among known cosmic bodies. By this indicator, it is 5 million times faster than the Sun. The blue star is located at a distance of 7.5 thousand light years from us.
• Class B has a temperature of 10-30 thousand Kelvin, a mass 18 times higher than the analogous parameter of the Sun. These are white-blue and white stars. Their radius is 7 times greater than that of the Sun.
• Class A is characterized by a temperature of 7.5-10 thousand Kelvin, a radius and mass exceeding in 2.1 and 3.1 times, respectively, similar parameters of the Sun. They are white stars.
• Class F: temperature 6000-7500 K. The mass is more than 1.7 times sunny, the radius is 1.3. From Earth such stars also look white, their true color is yellowish white.
• Class G: the temperature of 5-6 thousand Kelvin. The Sun belongs to this class. The visible and true color of such stars is yellow.
• Class K: temperature 3500-5000 K. The radius and mass are less than solar ones, are 0.9 and 0.8 of the corresponding parameters of the luminary. The color of these stars visible from Earth is yellowish orange.
• Class M: the temperature is 2-3.5 thousand Kelvin. The mass and radius are 0.3 and 0.4 from the analogous parameters of the Sun. From the surface of our planet they look red-orange. To class M belong to Beta Andromeda and Alpha Lisichki. A bright red star, familiar to many, is Betelgeuse (the alpha of Orion). It is best to look for it in the sky in winter. The red star is located higher and slightly to the left of the Orion belt.

Each class is divided into subclasses from 0 to 9, that is, from the hottest to the coldest. The numbers of stars denote belonging to a certain spectral type and degree of heating of the photosphere in comparison with other luminaries in the group. For example, the Sun belongs to the class G2.

Visual white

Thus, classes of stars from B to F from the Earth may appear white. And only objects related to the A-type, have this coloring in fact. Thus, the star Saif (constellation Orion) and Algol (beta Perseus) to the observer, who is not armed with a telescope, will appear white. They belong to the spectral class B. Their true color is white-blue. Also Mithrack and Procyon seem to be white, the brightest stars in the celestial drawings are Perseus and the Small Dog. However, their true color is closer to yellow (class F).

Why are the stars white for the terrestrial observer? Color is distorted because of the huge distance separating our planet from similar objects, as well as the voluminous clouds of dust and gas, often found in space.

Class A

White stars are characterized by not so high temperature, as representatives of class O and B. Their photosphere is heated to 7.5-10 thousand Kelvin. The stars of the spectral class A are much larger than the Sun. Their luminosity is also greater - about 80 times.

In the spectra of A stars, the hydrogen lines of the Balmer series are strongly pronounced. The lines of other elements are noticeably weaker, but they become more significant as we move from subclass A0 to A9. For giants and supergiants belonging to the spectral class A, slightly less pronounced hydrogen lines are characteristic than for stars in the main sequence. In the case of these luminaries, the lines of heavy metals become more noticeable.

A number of peculiar stars belong to the spectral class A. Such a term denotes luminaries, which have noticeable features in the spectrum and physical parameters, which makes it difficult to classify them. For example, quite rare stars such as lambda Bootes are characterized by a lack of heavy metals and very slow rotation. Among the pecular luminaries are also white dwarfs.

Class A belongs to such bright objects of the night sky as Sirius, Mencalinan, Aliot, Castor and others. We will get to know them closer.

Alpha of the Great Dog

Sirius is the brightest, though not the nearest, star in the sky. The distance to it is 8.6 light years. For the terrestrial observer, it seems so bright because it has impressive dimensions and yet it is not removed as much as many other large and bright objects. The nearest star to the Sun is the Alpha Centauri. Sirius is in fifth place on this list.

It refers to the constellation of the Great Dog and is a system of two components. Sirius A and Sirius B are separated by a distance of 20 astronomical units and rotate with a period of just under 50 years. The first component of the system is the star of the main sequence, belongs to the spectral class A1. Its mass is twice the solar mass, and the radius is 1.7 times. It can be observed with the naked eye from the Earth.

The second component of the system is a white dwarf. Star Sirius B is almost equal to our luminary by mass, which is not typical for such objects. Usually white dwarfs are characterized by a mass of 0.6-0.7 solar. In this case, the dimensions of Sirius B are close to the terrestrial ones. It is assumed that the stage of the white dwarf began for this star about 120 million years ago. When Sirius B was located on the main sequence, it probably was a luminary with a mass of 5 solar and belonged to the spectral class B.

Sirius A, according to scientists, will move to the next stage of evolution in about 660 million years. Then he will turn into a red giant, and a little later - in a white dwarf, like his companion.

Alfa Eagle

Like Sirius, many white stars, whose names are listed below, because of the brightness and frequent mention in the pages of science fiction literature are well known not only to people who are fond of astronomy. Altair is one of these luminaries. Alfa Orla is found, for example, in Ursula le Guin and Stevin King. In the night sky, this star is well visible due to its brightness and relatively close location. The distance dividing the Sun and Altair is 16.8 light years. Of the stars of the spectral class A, only Sirius is closer to us.

Altair by weight exceeds the Sun 1.8 times. Its characteristic feature is a very fast rotation. One revolution around the axis of the star makes less than nine hours. The rotation speed in the equatorial region is 286 km / s. As a result, the "bright" Altair is flattened from the poles. In addition, because of the elliptical shape from the poles to the equator, the temperature and brightness of the star decrease. This effect is called "gravitational darkening".

Another feature of Altair is that its brightness changes with time. It refers to variables such as the Shield Delta.

Alpha Lira

Vega is the most learned star after the Sun. Alpha Lyra - the first star in which the spectrum was determined. She became the second after the Sun luminary, captured in the photo. Vega also entered the number of the first stars to which scientists measured the distance by the method of the parliament. For a long period, the luminosity was taken as 0 in determining the stellar magnitudes of other objects.

Alpha Lyra is well acquainted with an amateur astronomer and a simple observer. It is the fifth in brightness among the stars, enters the asterism Summer Triangle together with Altair and Deneb.

The distance from the Sun to Vega is 25.3 light years. Its equatorial radius and mass are larger than those of our luminaries in 2.78 and 2.3 times, respectively. The shape of the star is far from the ideal ball. The diameter near the equator is noticeably larger than that of the poles. The reason is a huge speed of rotation. At the equator, it reaches 274 km / s (for the Sun this parameter is slightly more than two kilometers per second).

One of the features of Vega is the dust disk surrounding it. Presumably, it arose as a result of a large number of collisions between comets and meteorites. The dust disk rotates around the star and is heated by the action of its radiation. As a result, the intensity of the infrared radiation of Vega increases. Not so long ago discs were found asymmetric. Their probable explanation is that the star has at least one planet.

Alfa Gemini

The second brightest object in the constellation of Gemini is Castor. He, like the previous luminaries, belongs to the spectral class A. Castor - one of the brightest stars of the night sky. In the corresponding list it is located on the 23rd place.

Castor is a multiple system consisting of six components. The two main elements (Castor A and Castor B) revolve around a common center of mass with a period of 350 years. Each of the two stars is spectral-double. The components of Castor A and Castor B are less bright and pertain to the spectral class M.

Castor C was not immediately associated with the system. Initially, it was designated as an independent star of YY Gemini. In the process of studying this area of the sky it became known that this luminary is physically connected with the Castor system. The star revolves around a common for all components of the center of mass with a period of several tens of thousands of years and is also a spectral-double.

Beta Auriga

The sky figure of the Auriga includes about 150 "points", many of them are white stars. The names of the luminaries will say little to a person far from astronomy, but this does not detract from their significance for science. The brightest object of the heavenly figure, referring to the spectral class A, is Mencalinan or Beta Aurigae. The name of the star in Arabic means "the shoulder of the owner of the reins".

Mencalinan is a triple system. Two of its components are sub-gigants of spectral class A. The brightness of each of them exceeds the analogous parameter of the Sun by 48 times. They are separated by a distance of 0.08 astronomical units. The third component is a red dwarf, distant from the pair at 330 a. E.

Epsilon of the Great Bear

The brightest "point" in, perhaps, the most famous constellation of the northern sky (Big Dipper) is Aliot, also belonging to class A. The apparent value is 1.76. In the list of the brightest stars, the star ranks 33rd. Aliot is included in the asterism Large bucket and is closer to the other luminaries to the bowl.

The spectrum of the Aliot is characterized by unusual lines, fluctuating with a period of 5.1 days. It is assumed that the features are related to the action of the magnetic field of the star. Oscillations of the spectrum, according to recent data, can arise because of the close arrangement of the cosmic body with a mass of almost 15 masses of Jupiter. Is this so, while the mystery. Like other secrets of stars, astronomers try to understand it every day.

White dwarfs

The story of the white stars will be incomplete, if we do not mention the stage of the evolution of the stars, which is referred to as the "white dwarf". The name of such objects is due to the fact that the first ones found from them belonged to the spectral class A. It was Sirius B and 40 Eridan B. To date, white dwarfs call one of the variants of the final stage of the star's life.

Let us dwell in more detail on the life cycle of luminaries.

Star evolution

For one night the stars are not born: any of them passes several stages. First, a cloud of gas and dust begins to contract under the influence of its own gravitational forces. Slowly it acquires the shape of a ball, while the energy of gravity turns into heat - the temperature of the object rises. At the moment when it reaches a value of 20 million Kelvin, the reaction of nuclear fusion begins. This stage is considered the beginning of life of a full-fledged star.

Most of the time the luminaries are carried out on the main sequence. In their bowels there are constant reactions of the hydrogen cycle. The temperature of the stars may vary. When all the hydrogen in the nucleus ends, a new stage of evolution begins. Now the fuel is helium. In this case, the star begins to expand. Its luminosity increases, and the temperature of the surface, on the contrary, decreases. The star descends from the main sequence and becomes a red giant.

The mass of the helium nucleus gradually increases, and it begins to contract under its own weight. The stage of the red giant ends much faster than the previous one. The path along which further evolution will proceed depends on the original mass of the object. Malomassive stars at the stage of the red giant begin to swell. As a result of this process, the object resets the shell. The planetary nebula and the bare core of the star are formed. In this core all synthesis reactions were completed. It is called a helium white dwarf. More massive red giants (to a certain extent) evolve into carbon white dwarfs. In their nuclei there are heavier elements than helium.

Characteristics

White dwarfs are bodies, by mass, as a rule, very close to the Sun. At the same time, their size corresponds to the terrestrial one. The colossal density of these cosmic bodies and the processes occurring in their depths are inexplicable from the point of view of classical physics. Secrets of the stars helped to reveal quantum mechanics.

The substance of white dwarfs is an electron-nuclear plasma. It is almost impossible to design it even in a laboratory. Therefore, many characteristics of such objects remain incomprehensible.

Even if you study the whole night of a star, you will not be able to detect at least one white dwarf without special equipment. Their luminosity is much less than solar. According to scientists, white dwarfs make up about 3 to 10% of all objects in the Galaxy. However, to date, only those are found that are located no further than at a distance of 200-300 parsecs from the Earth.

White dwarfs continue to evolve. Immediately after the formation, they have a high surface temperature, but quickly cool down. A few tens of billions of years after the formation, according to theory, the white dwarf turns into a black dwarf - not emitting a visible light body.

A white, red or blue star for an observer is distinguished primarily by color. The astronomer looks deeper. The color for him immediately tells a lot about the temperature, size and weight of the object. A blue or light blue star is a gigantic red-hot ball, in all respects a strongly advancing Sun. White luminaries, examples of which are described in the article, are somewhat smaller. Numbers of stars in various catalogs also inform a lot of professionals, but not all. A large amount of information about the life of distant cosmic objects either have not yet been explained, or remain even unidentified.