These pages diplay and discuss the many objects we see in our universe. The emphasis is on high energy astrophysics data. 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. 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.
Most stars emit X-rays which satellites can detect.
These X-ray images look very different from what we see with our eyes. Notice the differences in the brightness of these stars in optical and X-ray light. Cosmic Journeys Part of the NASA OSS Structure and Evolution of the Universe theme.