The proton-proton chain reaction that fuses hydrogen into helium begins at a threshold of about 10 million degrees Kelvin. The fusion of helium doesn't begin until a temperature of about 100 million degrees Kelvin is reached. All the hydrogen must be exhausted and then a star must undergo further collapse for the new, higher threshold temperature to be reached to cause the initiation of helium fusion. Shazam! Now that's hot! Use the link below to our friends at Wikipedia for details.
The Sun's core is not yet hot enough, or under enough pressure, for helium fusion. Which is probably just as well, since when helium fusion begins, the Sun will swell into a red giant which will incinerate the Earth.
Fusion reactions need a certain amount of energy to get started. The energy, as indicated by the temperature, is simply too low in the sun's core (at THIS time) to fire up a helium fusion reaction. Wait a few billion years, and the amount of helium will build up so that the core will contract (thus compressing it and raising its temperature) to the temperature that He fusion can start.
In the core of the sun, helium is formed by the nuclear fusion of hydrogen isotopes.
helium is created in the solar core by combining hydrogen atoms in nuclear fusion.
Nuclear Fusion from hydrogen in it core and helium
Around the core of helium that been formed from hydrogen fusion.
Helium is formed in the core of the sun by the nuclear fusion reaction of hydrogen
Hydrogen undergoes nuclear fusion in the core of the sun to form helium.
Hydrogen undergoes nuclear fusion in the core of the sun to form helium.
No, it is formed by fusion of hydrogen and helium molecules.
Helium is formed in the core of the star (like the sun) by the nuclear fusion of hydrogen isotopes.
The Sun's energy is generated by nuclear fusion, the fusion of hydrogen into helium in the core of the Sun.