What are stars made of?
Stars are massive spheres of hot gas held together by gravity. Some stars are extremely massive – and some less massive – but most stars start out almost entirely made of hydrogen – with a smaller amount of helium. Hydrogen and helium atoms are the lightest atoms – and they’re also the oldest material in the universe. Only the first stars were made from this pristine stuff of matter created in the Big Bang. Stars don’t stay purely hydrogen and helium – because stars are so hot inside that hydrogen nuclei fuse to form heavier, more complex elements. This is fusion. Each fusion reaction results in a bit of leftover mass – which converts to light and heat. That’s how stars shine. Some of the first stars – formed early in the history of the universe – finished the first part of their evolution several billion years ago. And some of those stars exploded as supernovae – and spewed heavy elements like carbon, oxygen, and iron into space. Now most stars – including our sun – still contain most
Stars are made of very hot gas. This gas is mostly hydrogen and helium, which are the two lightest elements. Stars shine by burning hydrogen into helium in their cores, and later in their lives create heavier elements. Most stars have small amounts of heavier elements like carbon, nitrogen, oxygen and iron, which were created by stars that existed before them. After a star runs out of fuel, it ejects much of its material back into space. New stars are formed from this material. So the material in stars is recycled.
Basically, stars are big exploding balls of gas, mostly hydrogen and helium. Our nearest star, the Sun, is so hot that the huge amount of hydrogen is undergoing a constant star-wide nuclear reaction, like in a hydrogen bomb. Even though it is constantly exploding in a nuclear reaction, the Sun and other stars are so large and have so much matter in them that it will take billions of years for the explosion to use all the “fuel” in the star. The huge reactions taking place in stars are constantly releasing energy (called electromagnetic radiation) into the universe, which is why we can see them and find them on radio telescopes such as the ones in the Deep Space Network (DSN). Stars, including the Sun, also send out a solar wind and burst out occasional solar flares. The Saggitarius Star Cloud, found at the center of our galaxy. Star color is linked to temperature. A relatively cool, yellow star like our Sun would seem dim in this photograph. Hubble Space Telescope Image from the Astron
