Why do all stars in the universe not shine with the same amount of energy and have the same color and Why do they differ?

Answer 1

Due to material not being distributed evenly, some stars differ in how much mass they have. The greater the mass of a star, the more pressure there is at its core. Greater pressure at the core means that there is more heating by compression. Combined, greater heat and pressure mean that nuclear fusion, the energy source of a star, can take place more rapidly and in greater amounts. More nuclear fusion means more energy is released. The more energy a star releases, the brighter it shines and the hotter it is.

As a star gets hotter, its peak wavelgnth decreases, shifting from the red end of the spectrum tot he blue end. As a result, the coolest stars appear red while the hottest appear blue.