Copernicus in 1543 A.D. proposed the heliocentric view, which states that the Sun is the centre of the Universe instead of the Earth.
The Origin of the Universe
Big-Bang Theoery: By E. George lamantor. According to him, 15 billion years ago there was a big heavenly body, made up of heavy matters. Due to sudden explosion (Big Bang) of this heavenly body, normal matters came out of it. And many celestial bodies were created as a result of aggregation of these normal matters. Gradually their size increased due to continuous accumulation of normal matter around them. In this way, galaxies were created. Stars were formed due to re-explosion of these galaxies. In course of time, the planets were also formed in the same process.
A Galaxy is a large constellation of stars in which there is a central bulge and three rotating arms. Every galaxy is composed of about 100 billion stars. Our own galaxy is known as ‘Mandakini‘ which has spiral shape. A group of stars known as ‘Milky Way‘ seen in the night, is a part of our galaxy. Orian Nebula is the brightest and the coldest group ofstars of our galaxy.
Life Cycle of a Star
- Rotation of the galaxy causes the gaseous clouds present in the universe to become compact and due to the gravitation the process of nuclear fusion starts at the centre of this gaseous mass, converting hydrogen into helium. This process liberates an enormous amount of energy in the form of heat and light. At this stage the gaseous mass becomes a star. When star expands to a large size the temperature of the star at this stage also falls down, so it appears red. This is the Red Giant Star.
- Supernova : The helium starts converting into carbon and carbon into heavy metal like iron in the core. This results in a massive explosion in the which is known as supernova.
- Chandrasekhar Limit : If the initial mass of the star is less than 1.4 times the mass of the sun, then it ends its life as a white dwarf star, which is also known as a Fossil star. White dwarf ultimately turns into a Black dwarf. The limit 1.4 of solar mass has come to be known a Chandrasekhar Limit.
- Neutron Star: Unlike above, if the mass of the star is much more than the mass of the sun then it became Neutron Star.
- Black Hole: A Neutron Star remains contracting and, thus, mass in a large quantity, concentrates on one point. Such body with high density is called Black Hole. It does not allow anything to escape, including the light due to which it can be seen. It is John Wheeler who propounded the concept of Black Hole