Ask Dr. Universe: Gravity is a big reason why the sun is so hot

By Washington State University

Dr. Universe: Why is the sun so hot? – Ziyonna, 11, Indiana

Dear Ziyonna,

What happens if you do a big jump? Your body goes up into the air. But then it comes back down again. The reason you don’t just keep going up, up, up is because the force of gravity pushes your body and the Earth together.

It turns out gravity is a big reason the sun is so hot. That’s what my friend Michael Allen told me. He’s an astronomer at Washington State University.

He said that, at first, the universe was like a thick soup of gas and dust. Then, gravity pushed some of the gas and dust together. That’s how stars like our sun formed. It’s how planets and galaxies and everything else in the universe got there.

It’s how stars form today, too. Allen told me that, if you do the math, three new stars should form in the Milky Way galaxy this year – thanks to the pushes and pulls of gravity.

So, the sun exists because gravity pushed it together. That’s also why it’s hot.

As it was pushed and pushed from all sides, it became denser. That means there’s more stuff squeezed into a smaller space. It also became hotter–because pushing things together collects heat.

“That’s the first reason that stars like the sun are hot,” Allen said. “They’re the result of a process of collapse, and you can’t help concentrating heat and raising the temperature as a result of that process.”

All that pushing by gravity raises the sun’s temperature until it gets hot enough to change how the little bits that make up the sun – called atoms – behave.

Atoms like to bounce around. Normally, they crash into each other and bounce off each other.

But when it’s incredibly hot – over 10 million degrees – the atoms stop bouncing off of each other. Now, they crash into each other and stick together. That’s called nuclear fusion.

That happens really fast over and over inside the sun. Different kinds of atoms crash and stick in a cycle that turns hydrogen atoms into helium atoms.

All that crashing and sticking gives off even more heat and light. That’s how the middle of the sun gets up to a whopping 27 million degrees.

Eventually, the heat and light make their way to our planet. That’s why Earth is the warm, bright planet we know and love.

It’s all thanks to gravity pushing us around.

Sincerely,

Dr. Universe