Dear MacKenzie,
A neutron star is what’s left after a massive star runs out of fuel and explodes as a supernova.
I asked my friend Matthew Duez about it. He’s an astrophysicist at Washington State University.
He told me that a neutron star is the densest known object in the universe. Its mass is like the sun’s mass. But a neutron star is the size of a city.
When something is dense, it has lots of stuff—or mass—crammed into a small space.
Imagine if we took all the humans on the planet and squished them together. We mash and squash them until they fit into a space the size of just one die from a pair of dice. That’s a density like a neutron star’s density.
Think how heavy that die would be. If we scooped out a bit of neutron star that same size, it would weigh a billion tons. That’s as much as a billion cars.
A baseball-sized chunk of neutron star would weigh even more.
Duez told me that if we grabbed a baseball-sized bit of the inside of a neutron star, it would explode.
“The intense gravity of a neutron star squeezes the matter inside of it to extremely high pressure,” he said. “Taken suddenly away from the neutron star interior, its own high pressure would make a piece of neutron star matter blow outward in all directions.”
But let’s say we magically get that neutron ball to Earth. We gently set it on the ground.
Earth’s crust won’t be able to withstand all that weight and pressure in such a small area. The neutron ball will sink.
“It’s going to be pretty much free-falling,” Duez said. “So, it’s going to sink down to the core and then bounce around in there a bit.”
Our neutron ball will pick up speed as falls. It will overshoot the core and pass to the other side. Then Earth’s gravity will tug it back toward the center. It will change direction and pass the center and get tugged back by gravity again.
It’s like what happens on a playground swing. You swing way up in front of you. Then gravity pulls the swing back down. You swing way up behind you. Then gravity does its thing again.
As the neutron ball goes back and forth, it will pick up bits of rock. It will get bigger. Eventually it will slow down until the neutron ball settles in the Earth’s core.
Duez told me this all changes if we don’t set our neutron ball down gently.
Maybe we throw it down hard enough to overcome Earth’s gravity—called escape velocity. Then our neutron ball will pass through the whole planet. It will zoom off into space.
Or we could throw the neutron ball horizontally. Then it will orbit the center of the Earth, following an oval-like path instead of just bobbing up and down. If we throw it forward with just the right, very high speed, it might circle the Earth and come back to us from behind.
Like a super-dense, kinda-scary boomerang.
Sincerely,
Dr. Universe