The smallest red dwarf stars can smolder in the main sequence phase for an estimated 10 trillion years! The largest supergiant stars might only last a few million. Main sequence stars like our sun have a hot, dense core where hydrogen is fused into helium. Our Sun has already been in its main sequence for 4.5 billion years, and will probably last another 7.5 billion years before it runs out of fuel. The Main Sequence is where stars spend most of their lives. But the main sequence phase can last a long time. Over time, a star slowly uses up the supply of hydrogen in its core, and leftover helium builds up. Main sequence stars gravitational attraction tends to collapse the star radiation pressure from the fusion reactions tends to expand the star forces caused. This journey can take more than 100,000 years for a single photon to get from the core of a star out to its surface. The material cools down and falls back down inside the Sun where it’s heated up again. The higher the temperature in the central regions, the faster the star races through its storehouse of central hydrogen. Energy is then carried through a convective zone, where columns of hot plasma carry bubbles of heated gas to the surface of the Sun where it’s released. Large, bright, though cool, stars called giants and supergiants appear in the upper right, and the white dwarfs, dim, small, and. The energy released in the core must then travel slowly through a radiative zone, where photons of energy are absorbed and then re-emitted. The group called the main sequence extends in a rough diagonal from the upper left of the diagram (hot, bright stars) to the lower right (dim and cool). More massive main sequence stars are hotter, and are found at the top left of the strip. ![]() It’s inside this region where all the energy of the Sun is released. Main sequence stars are hydrogen-burning stars like our Sun. ![]() In a star like our Sun, the core accounts for about 20% of its radius.
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