In this episode of Cosmically Curious, host Patrick McNamee sits down with Saint Anselm College astronomer Nicole Gallucci to clear up some common black hole myths, explain the bizarre physics of spaghettification, and reveal what would actually happen if our sun suddenly turned into a black hole.
Transcript:
Patrick McNameeKing: So, Nicole, I know from sci-fi movies that black holes are like massive pools of gravity or something. What exactly are they, and why haven't I been sucked in?
Nicole Gallucci: Black holes don't have a great reputation, particularly in old-timey sci-fi.
And in our imaginations, we think of black holes as sucking everything into it. They're not like vacuums, right? Your vacuum cleaner actually pulls due to changes in pressure and all that. A black hole doesn't do that. It pulls with gravity, just like any other object that has gravity.
So, for example, if the sun in our solar system was replaced with a black hole of the same mass as the sun, that would suck for a lot of reasons, right?
Because we'd have no light, and then we'd have no energy, and then the plants would die, blah, blah, blah. But our orbit would hardly change at all. Earth would just keep orbiting around it due to that amount of mass.
Patrick McNameeKing: Okay, good to know. But they can pull things apart, right?
Nicole Gallucci: You have to get really close to a black hole to start seeing the effects where things get torn apart and pulled in through a process called "spaghettification," and its range is very limited.
It's only things that get super, super close to it that are going to be pulled into the range where things get distorted. Everything else is just going to keep orbiting around it, just like any gravitational object.
Patrick McNameeKing: Does a black hole change as it absorbs spaghettified particles?
Nicole Gallucci: Yeah, it does grow in mass as things, you know, disappear behind its event horizon and essentially become part of it.
The way that the matter gets there is interesting, because when you're close to a supermassive black hole, gravity doesn't work the way it does in our everyday life. It works more as described by Einstein in general relativity, where space is warped and time is warped.
And so if you're close to a black hole — say, your feet are pointing towards the black hole and your head is pointing away — you're feeling a much stronger gravitational pull on your feet than you are on your head. And if you're close enough, it's a strong enough gravitational pull that, you know, you are no longer a solid entity.
Patrick McNameeKing: Terrifying. Nicole. Thanks as always.
If you have questions about the night sky, send us an email at cosmic@npr.org.
