Solar core

The Sun’s innermost region, where extreme pressure and temperature sustain nuclear fusion. Energy produced there moves outward through the Sun before escaping as sunlight and other radiation.

Proton–proton chain: A sequence of nuclear reactions that fuses hydrogen nuclei into helium, releasing energy and neutrinos. This reaction sequence supplies nearly all the energy generated in the present-day Sun.
Solar mass: The mass of the Sun, used as a standard unit for comparing stars and other astronomical objects. The Sun’s mass sets the gravitational pressure that compresses its core.
Solar nebula: The cloud of gas and dust from which the Sun and Solar System formed. Gravitational collapse of this material built the young Sun and compressed its center.
Solar neutrino oscillation: The transformation of solar neutrinos among their three flavors as they travel. Flavor changes explain why early detectors counted fewer electron neutrinos than core models predicted.
Hydrostatic equilibrium: The balance between inward gravity and outward pressure in a star or other self-gravitating object. Pressure from the hot core balances the Sun’s gravitational compression.
Stellar nucleosynthesis: The formation of atomic nuclei through nuclear reactions inside stars. Core fusion is the Sun’s present-day contribution to this broader process.
Solar formation: The process by which the Sun formed from a collapsing region of a molecular cloud. The core emerged as the forming Sun’s central gas heated and became dense.
Helioseismology: The study of the Sun’s internal structure using observed oscillations at its surface. Oscillation data constrain interior sound speeds and indirectly test models of the core.
Solar neutrino: A weakly interacting particle produced in nuclear reactions, including those powering the Sun. Neutrinos escape from the core almost immediately, carrying direct evidence of its fusion reactions.
Hydrogen: The lightest chemical element, whose nuclei serve as the Sun’s primary fusion fuel. Hydrogen nuclei are the starting material for the core’s main energy-producing reactions.

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SunBroader topic: Fusion in the core releases the energy that eventually emerges from the Sun.