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Stars

Stars can be of widely varying sizes and colours. The oldest stars are swollen, red giants. Betelgeuse is a red supergiant. Old stars are much bigger—and cooler—than young, blue ones like Rigel, even though Rigel is 40 times bigger than the middle-aged Sun. A white dwarf, the collapsed core of an old star, is, however, tiny when compared to the Sun.Stars of varying sizes and typesStars can be of widely varying sizes and colours. The oldest stars are swollen, red giants. Betelgeuse is a red supergiant. Old stars are much bigger—and cooler—than young, blue ones like Rigel, even though Rigel is 40 times bigger than the middle-aged Sun. A white dwarf, the collapsed core of an old star, is, however, tiny when compared to the Sun. Stars are giant spinning balls of hot gases. They produce vast amounts of energy, including heat and light, which they radiate across space as they shine. They vary enormously in size (Betelgeuse in the constellation of Orion is 800 times the size of the Sun), and by the amount of light they give off. Stars come in different colours—according to how old they are. Blue stars are young and hot; red stars are old and cool. Orange and yellow stars (including the Sun) are young to middle-aged and moderately hot.

The Orion Nebula, a typical region of dust and gas where new stars are formingThe Orion NebulaThe Orion Nebula, a typical region of dust and gas where new stars are forming
A protostar, surrounded by a disc of dust and gas, known as an accretion disc, that may eventually form a system of planets around the star.A protostar surrounded by a disc of dust and gasA protostar, surrounded by a disc of dust and gas, known as an accretion disc, that may eventually form a system of planets around the star.

How stars form

A star is born when a cloud of dust and gas in space, known as a nebula (1), compresses under the force of gravity to become a dense blob, called a protostar (2) The shock waves from an exploding star at the end of its life nearby may be responsible for triggering this process. The protostar becomes so hot that it starts to produce its own energy in its core. Soon, gas and dust are blasted away. Sometimes, a spinning disc of gas and dust surrounds the newly forming star, which may eventually become the birthplace of new planets.

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Stars

How stars form

About 85% of all stars are red dwarfs (stars with a mass of less half that of the Sun), but none can be seen from Earth with the naked eye.