Hubble Identifies Source of Ultraviolet Light in an Old Galaxy

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October 26, 1999: The Hubble telescope's sharp vision has clearly seen - for the first time - hot blue stars deep inside an elliptical galaxy. Hubble confirms that the ultraviolet light emanating from this galaxy comes from a population of extremely hot, helium-burning stars at a late stage in their lives. The swarm of nearly 8,000 blue stars resembles a blizzard of snowflakes near the core of the neighboring galaxy M32, 2.5 million light-years from Earth in the constellation Andromeda.

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Q & A: Understanding the Discovery

1. 1. Why is this finding significant?




Thirty years ago, astronomers assumed that old groups of stars were relatively cool and extremely faint, thus releasing very little ultraviolet light. Then, observations by ground-based telescopes indicated that elliptical galaxies - football-shaped objects comprising old stars - were surprisingly bright when viewed in ultraviolet light. Since then, indirect evidence has traced the "light" to populations of old, hot, helium-burning stars. Now Hubble has provided the first direct evidence.

2. 2. What are helium-burning stars?




After stars exhaust their supply of hydrogen - their main source of thermonuclear fuel - they begin converting helium to carbon through nuclear fusion. This brief interlude in a star's life begins its downward spiral that eventually leads to their demise.