Stars– what are they made of? Mostly, just hydrogen and helium on fire out in space. The sun closest to us is our Sun, which has been burning for 4.5 billion years! Stars burn for what seems like forever, but eventually, they run out of fuel and stop being stars like we know them. What happens to the stars is dependent upon how big they are: for example, our Sun is relatively small, which means it goes through it’s fuel more slowly than a bigger star.
Think of it this way: have you ever noticed how dads eat way more than their daughters? Of course, the reason seems obvious–it’s because dad’s are bigger and need more “fuel” to keep them going. The same with a semi-truck vs a sedan, and a big star vs a small star. The bigger it is, the faster it will use its resources; the smaller it is, the less energy it needs and therefore doesn’t consume as much.
When our star runs out of hydrogen, it will begin to collapse in the core. That collapsing causes the star to get really hot, which makes the outer layers of the star expand. Expanding cools the star slightly and it becomes a Red Giant. Maybe you’ve heard of the red supergiant Betelgeuse? It’s the red dot you can see in the sky, close to Orion’s Belt!
After our sun becomes a red giant, it will start using helium as fuel. The star will compress and shed layers, compress and shed layers, until it becomes a White Dwarf star.
Bigger stars don’t stop fusing when they run out of helium and hydrogen, they fuse all the elements down the periodic table until getting to iron. After fusing iron, the gravitational pull inside the star gets so massive that the star can’t hold up any more. It implodes, then explodes, and all that’s left is a neutron star. Neutron stars are extremely dense, because it took a star with 5x the mass of the sun and compacted it all into something the size of a small city. Below is a picture from NASA of a neutron star.
With the biggest types of stars, when they finish fusing all their materials and collapse, the gravity pulls so hard that a star that was originally 10x the mass of the sun is swallowed and condensed into something around the size of a pea–better known as black holes. Black holes have such a giant gravitational pull that light doesn’t even escape! There are even things called supermassive black holes, and they’re believed to be at the center of every galaxy.
Check out NASA’s Astronomy Picture of the Day, which is a great source for fascinating photos!
Special thanks to Carla June Carroll (has her bachelor’s in Astronomy!) for helping out with this show. We couldn’t have even began to do this without her help!
Featured Image: Tom Hall