The characterization of celestial bodies can be very confusing. Only stars have visible, absolute magnitude, luminosity and other parameters. With the latter we will try to figure it out. What is the luminosity of stars? Does it have something in common with their visibility in 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 is a dense core in which nuclear reactions occur. They 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) may be contained. The greatest amount of hydrogen and helium in young stars, over time, their proportions decrease, giving way to other elements.
In the interior of the star, the atmosphere is very “hot”. The temperature in them reaches several million Kelvin. There are continuous reactions in which hydrogen is converted to 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 emissions of energy. Luminosity is a physical quantity that reflects exactly how much energy a celestial body produces in a given time.
It is often confused with other parameters, for example, with the brightness of stars in the night sky. However, brightness or apparent magnitude is an approximate characteristic that cannot be measured at all. It is largely related to the remoteness of the star from the Earth and describes only how well the star is visible in the sky. The smaller the number of this value, the greater its apparent brightness.
In contrast, the luminosity of stars is an objective parameter. It does not depend on where the observer is. This is the characteristic of a star, which determines its energy power. It can change at different periods of the evolution of the celestial body.
Approximate to luminosity, but not identical, is the absolute magnitude. It indicates the brightness of the star, visible to the observer at a distance of 10 parsecs or 32.62 light years. It is usually used to calculate the luminosity of stars.
Luminosity determination
The amount of energy that a celestial body releases is determined in watts (W), joules per second (J / s) or 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 you know the absolute value of the desired star. So, the Latin letter L denotes luminosity, the letter M is the absolute magnitude, and Ma is the absolute value of the Sun (4.83 Ma).
Another way involves great knowledge about the luminary. If we know the radius (R) and temperature (T ef ) of its surface, 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 the cosmic body with this value. So, there are objects thousands or millions of times weaker or more powerful than the Sun.
Star luminosity classes
To compare stars among themselves, astrophysicists use different classifications. They are divided by spectra, sizes, temperatures, etc. But most often, for a more complete picture, several characteristics are used at once.
There is a central Harvard classification based on the spectra that emit luminaries. It uses Latin letters, each of which corresponds to a specific color of radiation (O-blue, B - white-blue, A - white, etc.).
Stars of the same spectrum can have different luminosities. Therefore, scientists developed the Yerkes classification, which takes into account this parameter. She divides them by luminosity, based on the absolute value. Moreover, not only the letters of the spectrum, but also the numbers responsible for luminosity are attributed to each type of star. So, allocate:
- hypergiants (0);
- the brightest supergiants (Ia +);
- bright supergiants (Ia);
- normal supergiants (Ib);
- bright giants (II);
- normal giants (III);
- subgiants (IV);
- dwarfs of the main sequence (V);
- subwarf (VI);
- white dwarfs (VII);
The greater the luminosity, the lower the absolute value. For giants and supergiants, it is indicated 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 back in 1910. The diagram combines the Harvard and Yerkes classifications and allows us to consider and classify the luminaries more holistically.
Luminosity difference
The parameters of the stars are highly interconnected. The luminosity is influenced by the temperature of the star and its mass. And they depend a lot on the chemical composition of the star. The mass of a star becomes greater, the less heavy elements in it (heavier than hydrogen and helium).
Hypergiants and various supergiants have the largest mass. They are the most powerful and brightest stars in the Universe, but at the same time, 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 now known is the blue hypergiant R136a1. Its luminosity exceeds solar by 8.7 million times. A variable star in the constellation Cygnus (P Cygnus) exceeds the Sun in luminosity by 630,000 times, and 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 solar.