Heavy stars burn up faster and grow old more rapidly than less massive stars.
As all the stars of the Pleiades cluster formed at the same time, scientists can see how the mass of each star affects its luminosity, colour and ageing. Theories of stellar evolution, worked out using the Pleiades and other clusters of stars, under- pin all efforts to understand the Universe and to predict, for example, how long the Sun will survive. But when Hipparcos measured the distance of the Pleiades, the theories looked wrong. At 385 light-years, the star cluster is 10 percent closer than previously thought. The stars are 20 per cent less luminous - a huge discrepancy with the standard theories.