Wed. Dec 7th, 2022

It is always a beautiful sight to watch the sky. Especially when it’s dark, you can find most of the celestial objects. A sky is a celestial sphere filled with stars, planets, a sun, a moon, and other celestial objects. It appears in various spectacular colours due to atmospheric variations. The sky appears blue because the earth’s atmosphere scatters short-wavelength light more than long-wavelength light. The sun emits a wide range of wavelengths, but only those in the blue part of the spectrum make it through the atmosphere to reach our eyes.

Natural celestial bodies include stars and planets, while artificial ones include satellites and human-made space stations. We shall look at the most visible celestial object in the sky, the stars. Let us also know about the classification of stars and the Chandrasekhar limit.

Stars and Its Classification

Stars are a type of celestial body created from the fusion of hydrogen atoms. They come in many colours and sizes and have different amounts of mass. Stars live for billions of years until they exhaust. When a star dies, it either becomes a black hole or neutron star, depending on its mass. The classification of stars is based on their luminosity, determined by their surface temperature. In general, stars with higher temperatures are brighter than those with lower temperatures. The temperature can be measured using the magnitude system. The nearest star to earth is the sun.

Classification of the star is based on two schemes: the Harvard system and the MK system. In the decreasing order of temperature, there are seven main types of stars – O, B, A, F, G, K, and M.

Stars are classified by their size, colour, and other physical properties. They are classified as dwarf stars or giant stars based on their appearance. The most massive stars are the blue supergiant, which is more massive than the sun. Some types of stars based on evolution are the red giant star, protostar, T Tauri star, red dwarf star, main sequence star, white dwarf star, and neutron star.

White Dwarf and Chandrasekhar Limit

The maximum mass of a stable white dwarf star is known as the Chandrasekhar limit. It is named after Indian astrophysicist Subrahmanyan Chandrasekhar, who in 1930 first calculated the limit. The Chandrasekhar limit is an essential concept of physics that explains how large the star must be to be stable. Subrahmanyan Chandrasekhar found that if a white dwarf has more than 1.44 solar masses, the white dwarf will not be able to support its weight and will finally collapse into a black hole or neutron star. The size of the black hole could be up to 50 billion times the mass of the sun.

The Chandrasekhar limit is primarily important in two aspects:

  1. It determines how massive stars can be and still remain stable. If a white dwarf has more than 1.44 solar masses, it will not be able to support its weight and will collapse.
  2. It also determines the maximum mass of a white dwarf, the absolute limit that can be achieved before collapse occurs.

The different temperature and density layers in the earth’s atmosphere lead each stream of starlight that enters the atmosphere to be refracted or slightly altered. Hence, the stars appear to twinkle.

By Colleen