Yes, within stars, some matter is indeed converted into energy through nuclear fusion. In the cores of stars, where temperatures and pressures are extremely high, lighter atomic nuclei, such as hydrogen, fuse to form heavier nuclei, like helium. During this process, a small amount of the mass of the original nuclei is converted into energy, according to Einstein's mass-energy equivalence principle expressed by the equation \(E=mc^2\). This energy is released in the form of light and heat, providing the energy that powers the star and enables it to shine.
In more massive stars, other fusion processes can occur, leading to the formation of even heavier elements and additional conversions of matter into energy. This process is a fundamental part of stellar evolution and is responsible for the light and heat that stars emit.