Formation of the Sun and other stars
The Solar System was formed around 4.6 billion years ago from a giant cloud called a nebula, mainly made up of hydrogen gas and dust.
The nebula collapsed under its own gravity and, as it did, temperature and pressure increased.
It became denser and rotated more rapidly, spiralling inwards.
The hot core in the centre is called a protostar.
The collapsing and joining together of gas and dust under gravity is called accretion.
Eventually gravity compressed the hydrogen so much that the temperature reached about 15 million 0C.
At this temperature and pressure The joining together of two smaller atomic nuclei to produce a larger nucleus. Radiation is released when this happens. Nuclear fusion happens in stars like our Sun, and in hydrogen bombs. began and our Sun was born.
It is therefore called a A stable stage in the life cycle of a star. Nuclear fusion occurs, fusing hydrogen nuclei into helium nuclei. There is a balance between the outwards radiation and the force of gravity pulling inwards. star.
Brian Cox explains how the Earth was formed
In fusion reactions:
- hydrogen Nuclei is the plural of nucleus. The nucleus is the central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. fuse together to form helium nuclei;
- energy is released and radiates outwards.
A star, like the Sun, in its A stable stage in the life cycle of a star. Nuclear fusion occurs, fusing hydrogen nuclei into helium nuclei. There is a balance between the outwards radiation and the force of gravity pulling inwards. period, is stable - gravity tries to pull it inwards, and radiation pressure from the nuclear reactions tends to expand it outwards, but these forces are balanced.
In other words, the gravitational collapse inwards is balanced by the outward expansion due to heat and radiation pressure from the fusion reactions.
The Sun is expected to be a main sequence star for billions of years.