![]() ![]() Very massive stars use up their fuel quickly. The exact lifetime of a star depends very much on its size. Nuclear reactions at the centre (or core) of a star provides energy which makes it shine brightly. You can find out more about this subject in our guide to stellar classifications. The changes that occur in a star over time and the final stage of its life depend on a stars size. Only white dwarfs are normally plotted on an HR diagram. ![]() The surface temperatures of these stars are relatively cool since they are expanding, but they are very luminous, so they are plotted on the HR diagram above and to the right of the main sequence.Įventually, the star will reach the end point of its life and become a white dwarf, neutron star or black hole – again depending on its mass. Credit: Stocktrek Images/Tomasz Dabrowski / Getty Images Artist's impression of a star like our Sun swelling into a red giant and engulfing its orbiting planets. The star swells up and becomes a red giant or supergiant. The main sequence is not a sharply defined line on the HR diagram, though, as several other properties, like chemical composition and age, influence the location of a star on the diagram.Ī main sequence star is in a state of hydrostatic equilibrium – the internal pressure created by the nuclear reactions at the star’s core balances the inward pull of gravity, and the star is stable.īut once hydrogen burning in the core ceases, the star loses this stability and evolves away from, or off, the main sequence. Stars spend the majority of their lives on the main sequence the exact duration depends on the mass of the star.Īnd the main sequence is the most prominent curve on this diagram, forming a slanted ‘S’. This diagram is a graph of stars’ absolute magnitudes versus their surface temperatures. Stars in this phase lie on what we call the main sequence of the Hertzsprung-Russell (HR) diagram. The ‘main sequence’ part of the name refers to the fact that the Sun is at a stage in its life when the primary fuel source is the conversion of hydrogen to helium. Therefore, the combined color and luminosity class for the Sun is G2V (the same as alpha Centauri). A star whose characteristics place it in a band, called the main sequence, on an H-R diagram is called a main sequence star. The Sun is an example of a main sequence star, of spectroscopic type G2. The Sun is classified as a G-type main sequence star. Since our Sun is a star, we can classify it according to its spectral and luminosity classes. ![]()
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