The Sun is not a solid object; it is a massive sphere of superheated material held together by its immense gravity. The extreme temperatures and pressures inside the Sun prevent matter from existing in the familiar solid or liquid states found on Earth. Instead, the Sun’s matter exists in a highly energetic state, which is necessary for the star’s stability and function.
The Sun’s True State of Matter
The Sun is composed mainly of hydrogen and helium, but its matter exists in a state called plasma, often referred to as the fourth state of matter. Plasma is an ionized gas, meaning it is so hot that electrons have been stripped away from the atoms’ nuclei. This creates a superheated, electrically charged “soup” of positive ions and negative electrons that move freely.
The temperature in the Sun’s core reaches about 15 million degrees Celsius, which is too high for atoms to bond together to form molecules or a rigid structure. Because the particles are electrically charged, the Sun’s plasma is highly conductive and influenced by magnetic fields. This magnetic influence leads to solar phenomena observed on the surface, such as sunspots and solar flares.
Internal Structure and Zones
The Sun’s interior is organized into three distinct regions. The innermost region is the core, where temperatures and pressures are high enough to sustain nuclear fusion, converting hydrogen into helium and releasing enormous amounts of energy. About half of the Sun’s total mass is contained within this central region.
Surrounding the core is the radiative zone, where energy moves slowly outward through the absorption and re-emission of photons. The density in this zone is so high that a photon can take over 170,000 years to pass through it. The outermost layer is the convective zone, where the plasma is less dense and energy is transported by large-scale circulation currents. Hot plasma rises toward the surface, cools, and then sinks back down, moving the energy toward the visible surface.
Why Gravity Doesn’t Make It Solid
The Sun’s mass creates a powerful inward pull of gravity that constantly tries to compress the material toward the center. If this gravitational force were unopposed, the Sun would collapse in on itself. The phenomenon that prevents this collapse and maintains the Sun’s stable, spherical shape is known as hydrostatic equilibrium.
Hydrostatic equilibrium is the balance between the inward force of gravity and the outward pressure generated by the heat of nuclear fusion in the core. The core’s high temperature generates thermal pressure and radiation pressure, which push outward against the weight of the overlying layers. This continuous, self-regulating balance ensures that the Sun remains a stable ball of plasma for billions of years.