What exactly are stars?

STARS

Stars are huge spinning balls of hot, luminous gas. Each one is unique because stars differ in colour, temperature, size, brightness, and mass. Over time, characteristics change and the star evolves from one stage of star life to another. The key to a star’s life is its mass – the amount of gas it is made from. Mass determines the star’s life span, as well as its other characteristics and how these change.

  • STAR BIRTH Stars are formed inside vast clouds of hydrogen gas, such as the Eagle Nebula. A small fragment of cloud collapses under gravity. It becomes increasingly squashed and eventually forms a spinning ball of gas termed a protostar – the first sign of a new star.
  • MID-LIFE STARS Most stars glow steadily for most of their lives. During this stage they are known as main sequence stars – the Sun is one. Planets orbit around some stars; others, such as Fomalhaut, have discs of dusty material that may form planets.
  • YOUNG STARS A protostar gets denser and hotter as its gas becomes more squashed. When its core reaches about 10 billion °C (18 billion°F), nuclear reactions start. Hydrogen is converted to helium, energy is produced, and the star shines. Stars born at the same time and from the same region of cloud exist as a cluster. Some clusters remain together for millions of years, but eventually their stars drift apart.
  • SUDDEN DEATH Ageing stars with eight or more times the mass of the Sun swell into enormous, unstable supergiant stars, which can end their lives in a sudden and spectacular explosion known as a supernova. The exploding star creates an extremely hot gas cloud called a supernova remnant, while its core can collapse to become a rapidly rotating, very dense pulsar or a black hole (where the core collapses in on itself under gravity until it is a hole in space). The material dispersed into space forms clouds, which in turn can give birth to new stars.
  • DYING STARS when a star with a mass of up to eight times that of the Sun runs out of hydrogen, it swells up, cools, and becomes a red giant. Eventually, the giant star ejects its outer layers and becomes a planetary nebula. The ejected gas slowly disperses, leaving behind a white dwarf – the tiny, slowly cooling core of the original star.

Picture Credit : Google

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