Every other Friday on Morning Edition, the Outside/In team answers a question from a listener about the natural world.
This week, Gilman in Tucson, Arizona asked, “How close can you get to a black hole before you get pulled in by its gravity?”
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If you’re planning your next rendezvous to the periphery of a black hole (which we strongly advise against) you’ll have to first calculate how strong its gravitational pull is.
Here’s the equation to calculate the force on an object, which accounts for the masses of both objects, and the distance between them:
Fgrav = (Gm1m2)/d2
- Fgrav = force due to gravity
- G = universal gravitational constant, or 6.673 x 10-11 Nm2/kg2
- m1 = mass of one object
- m2 = mass of the other object
- d = distance between the centers of the two objects
As the equation shows, the more mass an object has, the stronger its gravitational pull.
Take, for example, the closest black hole to us in the Milky Way: Sagittarius A.
It’s only a mere 30 times wider than our sun, but its mass is 4 million times bigger. That means its gravitational pull is about 3 million times stronger than Earth’s gravitational force.
“We’re talking about forces that our human brain cannot even understand,” says Naoufal Souitat, a space engineer with the Southwest Research Institute.
Black holes are so strong, Souitat says, “they would pull you apart millions of miles before you even get close to them… You’re going to get spaghettified.”
This is a technical term, it turns out. Objects that get sucked into black holes are stretched in the direction of the hole while simultaneously compressed as the atoms are pulled in at different rates and directions.
“Just the difference in gravity between your feet and your chest is so huge. So you start being elongated and stretched out … until you become part of the black hole.”
The only way to get near a black hole without being spaghettified is to fly by really, really fast — in other words, to reach its escape velocity.
The same principle applies to rockets and satellites in orbit around Earth. For example, the International Space Station has to be moving at about 17,500 miles per hour in order to get a stable orbit around the planet.
Souitat did the math, and says that if you were 1 million miles away from Sagittarius A, you’d need to be traveling at 596,192 miles per hour to reach the escape velocity and avoid spaghettification.
But if you get too close, it doesn’t matter how fast you’re going — there’s no avoiding getting sucked in.
Inside a black hole’s event horizon, gravity is so strong that even light can’t escape. And light travels at 186,000 miles… per second.
Try to beat that.
