Stars
Stars are massive, luminous spheres of plasma held together by gravity. They emit light and heat through nuclear fusion, primarily converting hydrogen into helium. This process releases vast amounts of energy, making stars the primary sources of light in the universe. Stars vary in size, temperature, and lifespan, and their life cycles—from formation in nebulae to potential endpoints as white dwarfs, neutron stars, or black holes—are fundamental to understanding cosmic evolution.