Dear Grady,
I was exploding with excitement to ask my friend Guy Worthey about supernovas. He’s an astronomer at Washington State University.
He told me a supernova is a very energetic explosion in space.
There are different kinds of supernovas. One kind—called a type II supernova—happens when a really big star dies.
“Why would a star bother to blow up?” Worthey said. “It seems dramatic. Human beings don’t blow up when they die.”
But humans don’t have cores that do nuclear fusion. Deep inside a star, protons and neutrons bang together and make new chemical elements. That nuclear fusion is why stars shine.
Our sun is a smaller star. It only fuses hydrogen and makes helium. When the hydrogen runs out, it’ll start fusing the helium. Someday—about five billion years in the future—the sun will run out of energy and start to die. But it’s not big enough to supernova.
To do that, a star needs to be at least eight times heavier than our sun. Those high-mass stars fuse all kinds of stuff in their cores—like carbon, neon, silicon and iron.
“They end up building this central part that’s full of ashes from all those fusion episodes,” Worthey said. “And that’s not stable. It collapses under its own weight, and then there’s kind of a bounce that comes out. That causes some more runaway fusion, and that propels this explosion.”
Inside the supernova, particles keep banging together. That makes heavy elements—like iron. The explosive power of a supernova throws elements out into the universe. That’s how those elements ended up on planet Earth.
Without supernovas, we wouldn’t have oxygen in the air. We wouldn’t have iron in our bodies to transport that oxygen. We wouldn’t have most other elements—like the silicon that powers the device you’re using to read this.
A supernova leaves behind a black hole or a neutron star. They both cram lots and lots of mass from the dead star into a super small space. That gives them tons of gravity. It’s why they’re so weird and interesting. Like how black holes are invisible because light can’t escape their gravity. Or how one teaspoon of a neutron star weighs as much as ten million cars.
Another kind of supernova is called type I. That happens when two stars orbit each other. One star may start siphoning the matter from its companion star—basically stealing its mass. Eventually, the star will lose so much that it collapses and explodes. A type I supernova can also happen when two stars collide.
These supernovas are more common and extra bright. Astronomers use their bright light like a ruler to measure distances in space.
But a supernova isn’t something astronomers see every day.
“Supernovas don’t happen that often,” Worthey said. “We’re kind of overdue for a supernova in our galaxy—which is exciting.”
Nobody knows which star will supernova next. It’s going to be an explosive surprise.
Sincerely,
Dr. Universe