The luminosity of stars. Classes of luminosity of stars

The characteristics of celestial bodies can be very confusing. Only stars have visible, absolute magnitude, luminosity and other parameters. We will try to understand the latter. What is the luminosity of stars? Does it have something in common with their visibility on the night sky? What is the luminosity of the Sun?

Nature of stars

Stars are very massive cosmic bodies that emit light. They are formed from gases and dust, as a result of gravitational compression. Inside the stars there is a dense nucleus in which nuclear reactions occur. They also contribute to the glow of stars. The main characteristics of the luminaries are the spectrum, size, luster, luminosity, internal structure. All these parameters depend on the mass of a particular star and its chemical composition.

The main "designers" of these celestial bodies are helium and hydrogen. In a smaller amount relative to them, carbon, oxygen and metals (manganese, silicon, iron) can be contained. The greatest amount of hydrogen and helium in young stars, with time their proportions decrease, giving way to other elements.

In the interior regions of the star, the situation is very "hot." The temperature in them reaches several million kelvins. Here there are continuous reactions in which hydrogen turns into helium. On the surface, the temperature is much lower and reaches only a few thousand Kelvin.

What is the luminosity of stars?

Thermonuclear reactions inside stars are accompanied by energy releases. Luminosity is also called the physical quantity, which reflects how much energy the heavenly body produces in a certain time.

It is often confused with other parameters, for example, with the brightness of stars in the night sky. However, the brightness or the apparent magnitude is an approximate characteristic that is not measured in any way. It is largely related to the remoteness of the luminary from the Earth and describes only how well the star is visible in the sky. The smaller the digit of this value, the greater its apparent brightness.

Unlike it, the luminosity of the stars is an objective parameter. It does not depend on where the observer is. This is a characteristic of the star, which determines its energy capacity. It can change at different periods of the evolution of the celestial body.

Approximate to luminosity, but not identical, is the absolute stellar magnitude. It denotes the brightness of the light, visible to the observer at a distance of 10 parsecs or 32.62 light-years. Usually it is used to calculate the luminosity of stars.

Luminosity determination

The amount of energy that the celestial body releases is determined in watts (watts), joules per second (J / s) or in ergs per second (erg / s). There are several ways to find the required parameter.

It is easy to calculate by the formula L = 0,4 (Ma -M), if we know the absolute value of the required star. Thus, the Latin letter L denotes luminosity, the letter M is the absolute stellar magnitude, and Ma is the absolute magnitude of the Sun (4.83 Ma).

Another way involves a lot of knowledge about the luminary. If we know the radius (R) and the temperature (T _ef ) Of its surface, then the luminosity can be determined by the formula L = 4pR ² sT ⁴ _ef . Latin s in this case means a stable physical quantity - the Stefan-Boltzmann constant.

The luminosity of our Sun is 3.839 x 10 ²⁶ Watts. For simplicity and clarity, scientists usually compare the luminosity of a cosmic body with precisely this magnitude. So, there are objects in thousands or millions of times weaker or more powerful than the Sun.

Classes of luminosity of stars

For comparison of stars among themselves, astrophysics use different classifications. They are divided according to spectra, sizes, temperatures, etc. But more often, for a more complete picture, several characteristics are used at once.

There is a central Harvard classification based on spectra that emit lights. It uses Latin letters, each of which corresponds to a particular color of radiation (O-blue, B-white-blue, A-white, etc.).

The stars of the same spectrum can have different luminosities. Therefore, scientists have developed Yerkes classification, which takes into account this parameter. It divides them according to luminosity, based on absolute magnitude. In this case, each type of star is attributed not only the letters of the spectrum, but also the numbers responsible for luminosity. So, they distinguish:

• Hyper-giants (0);
• The brightest supergiants (Ia +);
• Bright supergiants (Ia);
• Normal supergiants (Ib);
• Bright giants (II);
• Normal giants (III);
• Sub-giants (IV);
• Dwarfs of the main sequence (V);
• Sub-dwarfs (VI);
• White dwarfs (VII);

The higher the luminosity, the lower the value of the absolute value. In giants and supergiants it is denoted with a minus sign.

The relationship between the absolute magnitude, temperature, spectrum, and luminosity of stars is shown by the Hertzsprung-Russell diagram. It was adopted in 1910. The diagram combines the Harvard and Yerkes classifications and makes it possible to treat and classify luminaries more holistically.

The difference in luminosity

The parameters of the stars are strongly interrelated. The luminosity is influenced by the temperature of the star and its mass. And they depend a lot on the chemical composition of the light. The mass of a star becomes the greater, the less heavy elements in it (heavier than hydrogen and helium).

The biggest mass is possessed by hyper-giants and various supergiants. They are the most powerful and brightest stars in the universe, but at the same time, and the rarest. Dwarfs, on the contrary, have a small mass and luminosity, but make up about 90% of all stars.

The most massive star that is known now is the blue hypergiant R136a1. Its luminosity exceeds the solar one by 8.7 million times. The variable star in the constellation Cygnus (P Cygnus) is 630,000 times more luminous than the Sun, and the S of the Golden Fish exceeds this parameter by 500,000 times. One of the smallest known stars 2MASS J0523-1403 has a luminosity of 0.00126 from the solar.