Final answer:
The Sun is powered by nuclear fusion, a process where hydrogen nuclei fuse into helium, converting mass to energy, and enabling the Sun to emit energy for billions of years.
Step-by-step explanation:
The energy generation mechanism that can power the Sun for billions of years is nuclear fusion. This process involves converting very light nuclei, like hydrogen, into heavier nuclei, such as helium. In the Sun's core, four hydrogen nuclei (protons) undergo a series of reactions, known as the proton-proton chain reaction, to fuse and produce one helium nucleus and two positrons. During nuclear fusion, mass is converted into energy, following Einstein's equation E = mc², where E represents energy, m is mass, and c is the speed of light. This remarkable process releases tremendous amounts of energy, which is why the Sun has been able to shine for about 4.5 billion years and why it’s expected to continue for billions more.