Main-sequence stars are a category of stars that are in a stable phase of their life cycle, where they fuse hydrogen into helium in their cores. This process generates energy, which creates the outward pressure needed to balance the gravitational forces pulling inward. The majority of stars, including our Sun, are classified as main-sequence stars, and they can vary in size, temperature, and brightness. These stars are typically represented on the Hertzsprung-Russell diagram, a graph that plots stars based on their luminosity and temperature. Main-sequence stars range from small, cool red dwarfs to massive, hot blue giants. Their position on the diagram indicates their mass and age, with more massive stars burning through their hydrogen fuel more quickly than smaller ones.