DAVID A. HARDY / SCIENCE PHOTO LIBRARY DAVID A. HARDY / SCIENCE PHOTO LIBRARY
Artwork of the main stages in the life of a star. Stars are born (left) from the gravitational contraction of a cloud of gas. Due to the contraction, the temperature of the gas increases till it triggers the nuclear fusion of hydrogen atoms. The lower track shows the evolution of stars like our Sun. After all the hydrogen is burnt the star increases its diameter and becomes a red giant. Eventually the outer layers are shed exposing the helium-rich core of the star which becomes a white dwarf. More massive stars (upper track) undergo a red supergiant phase and then a supernova explosion which may leave behind either a black hole or a neutron star.
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