BI Answers: What Happens When You Enter A Black Hole?
In Christopher Nolan’s latest film, “Interstellar,” actor Matthew McConaughey dives into a black hole. Although Nolan and the special effects team, guided by a prestigious theoretical astrophysicist, Kipp Thorne, produced one of the most scientifically accurate visuals of a black hole for the film, you don’t get a good sense of what McConaughey’s character sees or feels as he falls toward the center, which is unfortunate because what a black hole does to the human body is really cool.
Astronomers estimate that our galaxy harbours approximately 100 million black holes. If you ever entered one, you would suffer a most horrible death and when it was all over, there would be no trace, no physical evidence that you ever existed.
Prior to your terrible demise, however, you would see and feel some amazing, powerful, and downright trippy, stuff.
Like planets and stars, there are both big and small black holes. You will die regardless of what size of black hole you enter. But the time it takes you to die upon approach and what you see beforehand strongly depends on your black hole of choice.
Let’s first look at the closest black hole to Earth, called V4641 Sgr for the star that orbits it. Black holes, by definition, are invisible, so astronomers usually find them by the stars and gas that orbit around them. Calculating the distance to a black hole is equally hard as finding one, but as far as we know, V4641 Sgr is between 1,600 and 24,000 light years away, located in the direction of the constellation Sagittarius.
Small But Deadly
V4641 Sgr is an example of a small black hole. It’s two to three times more massive than our sun, and all that mass is confined to a space less than 4 miles across. This means the center of the black hole, called the singularity, is incredibly dense and therefore has a colossal gravitational pull, strong enough to trap light and everything else that comes too close.
This also means that as you approach the black hole, you’ll see blackness blotting out light from distant stars. But that’s not all you’ll see. Black holes distort the space around them, which in turn, bends the path along which passing light travels. As a result, you’ll begin to see some very weird stuff upon your approach. Something like this:
The outer ring is the result of gravitational lensing, when gravity bends light, distorting and magnifying what we would otherwise see in the absence of a strong gravitational force. Anything with a strong gravitational pull can create gravitational lensing, including massive galaxies and galaxy clusters.
The edge of a black hole — outlining the black circle in the animation above — is called the event horizon. It is known as the point of no return, or the exit door of the universe. Whatever passes the event horizon, including you, can never return because the black hole’s pull is too strong to escape, even if you’re travelling at the speed of light.
However, you don’t have to worry about reaching the event horizon in this case because you’ll be dead long before that. Small black holes are especially lethal because they have very large tidal forces that will stretch you paper-thin before you even reach the event horizon.
This stretching action is called spaghettification because you look like a very long piece of unappetizing spaghetti when the tidal forces are done with you. One example of these tidal forces that will be pulling you apart, first explained by Isaac Newton, are tides on Earth. They’re caused by the gravitational interaction between the Moon and our planet.
Whichever side of Earth faces the Moon is the side that is closest and therefore feels the strongest gravitational tug compared to the opposite, farther side. The same thing happens to your body when you’re nearing a black hole. Here’s what spaghettification would do to a spacecraft:
Say you’re fearless — after all, you’re entering a black hole — and you go head-first toward the blackness. The top of your head is going to be closer to the black hole’s center, called the singularity, than your feet. As a result, gravity’s influence on your head will pull you toward the center of the black hole more than your feet, stretching you spaghetti-thin in the process.
Eventually, you’re stretched to the point you begin to break down into individual atoms. And it does not take an expert to tell you that this would be a most unpleasant way to die! If you try to enter a black hole, you will get spaghettified no matter what. But a small black hole is going to kill you faster than a supermassive black hole, like the one at the center of our home galaxy, the Milky Way.
Approximately 25,000 light years from Earth, at the center of our galaxy, there is thought to be a supermassive black hole that is 4.3 million times more massive than our sun. But, if you travel the distance to this larger black hole, you’ll get close to the event horizon, and even pass it while still alive and coherent. The view might make you feel a little off kilter at first but will be totally worth it:
Why can you get closer to a large black hole? It’s because the event horizon is farther from the center. This means that the tidal forces at the event horizon are weaker — if the Moon were farther from Earth, we would have smaller tides for the same reason. Therefore, you would not start to get spaghettified until after you entered the black hole.
As you fell closer toward the event horizon, the gravitational force around you would grow. This means it would bend the light that reached your eyes more strongly, which is what you’re seeing in the animation above. Moreover, time would tick more slowly the deeper you fell into the black hole.
From your perspective, time would tick on as usual, but from an outsider’s perspective, like someone on Earth, you would age very slowly. This phenomenon is called gravitational time dilation.
As you fall closer to the event horizon, the blackness will grow, eventually covering your entire field of view. When that happens, when you see only darkness, then you’ll know that you’re inside of a black hole. The last opportunity to see the universe you’re leaving, forever, will be directly behind you and will be a tiny point of light. After that, gravity will drag you toward the singularity at the speed of light and ultimately spaghettify you.
No one knows what happens beyond the event horizon, and astrophysicists suspect that the physics we understand here on Earth breaks down inside of a black hole. That means there’s no scientific way to explain or understand what goes on after you exit the universe.
Physicists are working on the problem in the laboratory by creating acoustic black holes — singularities that are strong enough to trap sound, but not light. The mathematics behind acoustic black holes are the same, however, which offers a good starting point to better understand what takes place inside these bizarre cosmic phenomena.
Nolan has one crazy theory, but you’ll have to watch “Interstellar” to find out!
(The animations in this post are what you would see as you approached a stationary black hole. In reality, most black holes, and possibly all, are spinning. This means they would distort the space around them even more, and as you approached the event horizon you would actually start to orbit around the center, which would slightly change what you saw. But you would still feel the same tug from tidal forces and experience gravitational time dilation.)
For more incredible animations on what it’s like to enter a black hole, check out this cool video.
This post is part of a continuing series that answers all of your “why” questions related to science. Have your own question? Email [email protected] with the subject line “Q&A”; tweet your question to @BI_Science; or post to our Facebook page.