What happens if you fall into a black hole?
It's time to jump into a black hole. I’ve now been sufficiently prepared for my voyage into the unknown and I am now coming to you from just outside of a supermassive black hole. I went with 'Sagittarius A', the supermassive black hole at the centre of the Milky Way. It has a mass of 4 million suns, and I’ll explain why I picked this one later, but for now let’s do this.
Will - The effects start slow. A black hole this big has probably been gravitationally influencing me even slightly for millions of miles at this point. Although up until now, I will have been able to escape it. The chances of escape, however diminishing the closer I get to the orbit of the black hole. How close before it's a noticeable pull, of course, depends on the size of the black hole. And I recall the words of wisdom from the royal observatory at Greenwich's Ed Bloomer...
Ed - I tried to do some back of the envelope calculation and I was working with a black hole that had twice the mass of the sun because that's about the lower limit of black holes you can traditionally make with supernovae. Once you're about five and a half million kilometers away, then the pull on your body just from that black hole would be about the same that you'd experience right now here on earth. So you feel like you weighed one standard earth gravity just because of that black hole.
Will - This black hole, however, is many, many times the size of that one though. So the feeling of earth-like gravity started a lot further away. The pool is increasing and it feels like I'm beginning to accelerate.
Ed - It's the nature of the gravity itself. The closer you are to the gravitating body, the stronger the pool and that accelerates somebody.
Will - More time passes, although not nearly as much time as we'll be passing on earth with such a massive time dilation. One minute here is about 700 years on our planet. So sorry if this goes out a bit late. Physics is starting to get really funky now because light is orbiting the black hole in a circle. If I look around, I might be able to see the back of me. The brightest object in the galaxy could now be my bald spot, but I can take solace in the fact that anyone observing my fault is seeing some pretty weird stuff too.
Ed - I don't want to go near this black hole. So let's say I watch you fall into it. From my point of view, I think you are slowing down and the time itself is passing at a different rate. As, as in fact it is. But also gravitational redshift is happening. The immense gravity of the black hole means that these electromagnetic radiation waves, whether that's radio or whether you're shining a torch at me or whatever, they're being stretched to larger and larger wave strengths. So actually, in fact you're not only just changing colour, eventually your radio signals are gonna be stretched out to the point where I can't actually receive, uh, anything from you or indeed see you anymore. Eventually you would lose vision as well.
Will - Good job. I'm recording this on a handheld device. Then eventually I hit the point of no return. If I were made of light, this would be the event horizon or the Schwarzschild radius. But given that I'm not, and my bathroom scales assure me that, it's a bit further out,
Ed - There's a point where you cannot maintain a stable orbit. And it depends on the situation. But let's say in the best case scenario about four and a half times what we call the Schwarzschild radius, which people sort of tend to think as the really the last stopping point, but actually about four and a half times further out than that. That's the point at which you are not going to be able to prevent yourself from falling into that black hole.
Will - Passing over this point. And then the event horizon, the forces of gravity coming from the singularity at the centre are conspiring to pull me apart. The difference in gravitational pull and the distance between my head and feet is so large that I would be pulled apart. Think of the centre of a black hole as a tube and the smaller the black hole, the smaller the tube I would be squeezed through. It's called spaghettification. It sounds like a grim way to go. And in smaller black holes that would be the case. But this is why I picked a supermassive black hole.
Ed - When you have much more mass in the black hole, the size of the black hole scale up with that mass. And what that means is when you have truly, truly massive black holes, the gradient is a little bit more gentle for you. And in theory, depending on the mass of the black hole, if you've got truly massive black holes, you could have a gradient that's gentle enough that spaghettification won't be the end of you, which means that you could actually get pretty close to the event horizon. But it would only be, I think about 25 times Earth's gravity.
Will - 25 times the gravity of Earth is barely anything. So assuming I've survived being squeezed, I am curious as to how I might meet my end.
Ed - It depends what else the black hole is doing because in fact as other objects fall into it, they accelerate and they produce x-rays and even gamma rays. So in fact, if other dust clouds and things like that, little particles are falling into the black hole, possibly long before you have a problem with, you know, the actual mechanics on your body, you're actually being blasted by gamma rays from the black hole. So incoming radiation might actually be the thing that kills you, I'm afraid.
Will - So I may well go out as a well done steak rather than a piece of spaghetti. Assuming neither of those happen, I enter the circle of the black hole as it consumes me. The rest of the universe now only looks like a circle of distant light that is rapidly fading. I mentioned physics was funky earlier, but now it kicks into overdrive. Due to the nature of the singularity's gravity, every direction is now inward. Any attempt to move away from the black hole would actually bring me closer towards the centre as we enter the singularity. What happens next is contentious. And depends if you think a black hole completely destroys the matter that it takes in or just compresses it down to near infinity. But either way, I'm stripped of my being and the atoms that made up my existence are crushed and joined the infinitely dense point. I become part of the black hole.