Keele

IAU Symposium 256
The Magellanic System: Stars, Gas, and Galaxies
28 July - 1 August 2008            Keele University (UK)

IAU
Outreach: Star Formation
Stars are usually formed in nebulae, large clouds of gas and dust. Gravity causes the nebula to collapse, which produces protostars. The new stars collapse again, to form main sequence stars. Our Sun is a main sequence star.

Life cycle of a starMain sequence stars convert hydrogen to helium in their cores. When the star runs out of hydrogen, the helium can be changed into heavier elements. The cores of the stars shrink and their surfaces expand and become cooler and dimmer. Stars the size of our Sun become red giants; stars more than one and a half times that of the Sun become red supergiants.

Sun-sized stars then form planetary nebulae as their outer layers drift into space. Planetary nebulae have nothing to do with planets. The stars form white dwarfs, which have no fuel and only glow because of heat energy left over from the hydrogen to helium conv
The 1987 supernovaersions. When the star cools, it becomes a black dwarf.

Larger stars explode. This is known as a supernova. Stars between one and a half and three times the size of the Sun become neutron stars with very strong gravity, which spin extremely quickly. Stars larger than three times the size of the Sun become black holes, which have gravity so strong that nothing can escape them, even light.

A supernova in the Large Magellanic Cloud in 1987 proved that neutron stars exist. Before the supernova, no neutron stars had been spotted, although astronomers thought that they existed.



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