Solar core

The Sun has a very hot center.

This part is called the core. It is the hottest part of our space neighborhood. In the core, tiny bits of gas join together. This makes a lot of heat and light.

This heat travels from the center to the outside. It moves through many layers to reach us. The core makes almost all the Sun's power. It is a busy and bright place.

The Sun has a very hot center. This part is called the core.

It is the hottest part of our solar system. The core is made of hot, thick plasma. Plasma is a state of matter made of ions and electrons.

Inside the core, a way of making power happens. We call this nuclear fusion. This happens when tiny bits of hydrogen join to make helium. Most of this power comes from the proton–proton chain reaction. Another way is the CNO cycle. This second way uses carbon to help.

The core is very heavy. It holds 34% of the Sun's mass. It makes 99% of the Sun's power. Every second, 600 million tonnes of hydrogen turn into helium. This lets out a lot of heat. This heat must travel through many layers. It can take 170,000 years to reach the edge. Tiny particles called neutrinos also escape the core. They can leave the Sun right away.

The Sun has a very special center called the solar core. This region is the hottest part of our entire solar system. It is a thick, heavy area made of hot plasma. Plasma is a state of matter made of ions and electrons. The core is not very large compared to the whole Sun. It only takes up about 3% of the Sun's total volume. However, it holds 34% of the Sun's total mass.

This small center is where almost all the Sun's energy begins.

Energy is made in the core through a process called nuclear fusion. This happens when tiny hydrogen nuclei join together to create helium. There are two main ways this works in the Sun. Most of the energy comes from the proton–proton chain reaction. A second way is called the CNO cycle. This cycle uses carbon atoms to help the process.

Both ways turn four hydrogen nuclei into one helium nucleus. This amazing process releases huge amounts of heat and light.

Scientists use models to understand how this power works. At the very center, the temperature is 15 million kelvins. The density there is 150 grams per cubic centimeter. The core is also a place of balance called equilibrium. If fusion happens too fast, the core heats up and expands. This expansion makes the fusion rate slow down again. If fusion slows down, the core cools and shrinks. This makes the fusion rate go back up.

Every second, the Sun does a massive amount of work. About 600 million tonnes of hydrogen turn into helium every second. This releases energy at a rate of 3.86 joules per second. The composition of the plasma changes as you go deeper. At the outer core, hydrogen makes up about 70% of the mass. By the time you reach the center, it drops to 34%. Most of the rest of the mass is helium.

This change happens because fusion uses up the hydrogen.

Once energy is made, it must find a way out. High-energy light particles called gamma rays start this long journey. They bounce around through many layers of the Sun. It can take about 170,000 years for them to reach the edge. Some tiny particles called neutrinos are also made during fusion. Unlike the light, neutrinos can escape the Sun almost immediately. They do not get stuck in the thick layers. This allows them to travel straight out into space.

The solar core is the dense, central region of the Sun.

It is the hottest part of our entire solar system. This region is where the Sun generates its energy through a process called nuclear fusion. While the core is physically small, it is incredibly important. It makes up only about 3% of the Sun's total volume. However, it contains 34% of the Sun's total mass.

This small area is responsible for generating 99% of the Sun's fusion power.

Nuclear fusion is the mechanism that powers the Sun. In the core, extreme heat and pressure force hydrogen nuclei to join together. This process eventually results in the creation of helium nuclei. There are two distinct ways this happens in the solar core. The first is the proton–proton chain reaction. This sequence is responsible for most of the Sun's released energy. The second is the CNO cycle, which uses carbon atoms to facilitate the reaction.

The CNO cycle generates less than 10% of the total solar energy.

The proton–proton chain reaction is a complex, multi-step process. It begins when four hydrogen nuclei eventually become one helium nucleus. This specific reaction sequence is thought to be the most important one for the Sun. The first step in this chain is quite slow. It can take about one billion years for the first reaction to occur. This is because the weak force must cause beta decay before the particles can adhere. However, the later steps happen much faster. For example, deuterium and helium-3 only last for about four seconds and 400 years, respectively. These later reactions proceed via the nuclear force. The total energy released in turning four hydrogen atoms into one helium atom is 26.7 MeV.

The composition of the solar plasma changes depending on the depth within the Sun. In the photosphere, or the Sun's outer visible layer, hydrogen makes up about 73% to 74% of the mass. As you travel deeper toward the center, the fraction of hydrogen decreases. This happens because fusion is actively consuming the hydrogen to create helium. At the outer edge of the core, hydrogen is about 70% of the mass. By the time you reach the very center, the hydrogen mass fraction drops to approximately 34%. At this central point, almost all of the remaining plasma mass is helium.

The core maintains a state of self-correcting equilibrium. This means the rate of fusion stays stable due to physical balance. If the fusion rate increases, the core heats up and expands. This expansion reduces the fusion rate, which corrects the change. If the fusion rate decreases, the core cools and shrinks. This shrinking increases the fusion rate once again. However, the Sun is not perfectly static over long periods. The core gradually becomes hotter during its time on the main sequence. This is because helium atoms are denser than the hydrogen they replaced. This increases gravitational pressure, which causes the fusion rate to increase over time. The Sun has become 30% brighter over the last 4.5 billion years.

The physical conditions in the core are extreme. At the very center, the temperature reaches 15 million kelvins. The density at the center is 150 grams per cubic centimeter. The pressure at the center is estimated at 265 billion atmospheres.

Every second, about 600 million tonnes of hydrogen are converted into helium. This massive conversion releases energy at a rate of 3.86 joules per second. Interestingly, the peak power generating density at the center is about 276.5 watts per cubic meter. This density is actually similar to an active compost heap. It is even lower than the power density produced by a human's metabolism. The Sun's massive size is what makes it so powerful despite this.

Once energy is created, it must travel from the core to the surface. High-energy photons, known as gamma rays, begin this journey. They do not move in a straight line. Instead, they undergo random scattering from free electrons in the radiative zone. This makes the journey very slow. It takes about 170,000 years for these photons to reach the edge of the radiative zone. Eventually, they enter the convective zone, where heat moves much faster. During this long trip, each gamma photon is converted into millions of visible light photons.

Another product of fusion is the neutrino. Unlike light, neutrinos rarely interact with matter. This allows almost all neutrinos to escape the Sun immediately.