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What are Stars?A star is a dense mass that generates its light and heat by nuclear reactions, specifically by the fusion of hydrogen and helium under conditions of enormous temperature and density. When the hydrogen atom merges with the next heavier element, helium, mass is lost, thus the mass is converted to hydrogen (E=mc^2). The sun, which is our closest star, is powered by hydrogen fusion. The fusion only takes place at core of the star where it is dense enough.
How does X-ray Astronomy Fit In?Most stars emit X-rays which satellites can detect. These X-ray images look very different from what we see with our eyes. They show us the hotter areas of gas surrounding stars (stellar coronae), the hottest stars (young white dwarfs), and flares from stars.
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