Archived Content Red giants are the telltale signs of aging in stars. Like people, stars are born and die. These nuclear reactions power the stars at the same time that they halt the stars' collapse by counterbalancing gravity. In this state of quasi-equilibrium, stars burn hydrogen contentedly for millions to billions of years, depending on their masses.
Large stars burn hotter and more quickly than do smaller ones.
The Sun, an average star now at the midpoint in its life, is 5 billion years old. In another 2 to 5 billion years it will exhaust its hydrogen fuel and begin the dramatic transformation to a red giant. Woodward and Porter's interest in these aging stars is their vigorous convective envelopes. In younger stars, heat from nuclear fusion finds its way to the surface primarily through radiative diffusion. Only during the cooler last third of their journey is this heat transported by convective motions of stellar gas.