Well, time itself flows at different rates depending on what is happening. Hold on, isn’t time… time? How can we be experiencing it so differently? You, meanwhile, are experiencing time pass normally. Remember, I’m finding it increasingly hard to even detect you, since your radio signals for help and any other photons you’re emitting are being stretched to longer and longer wavelengths. As far as I’m concerned, time is literally passing more slowly for you than for me.īy my calculations, your passage through time is going to crawl to a halt as you approach the event horizon. Time dilation means that from my perspective you actually start to slow down as you fall into the black hole. Let’s assume I am still in that distant space station you signalled for help. Things will look quite different to observers in different positions. But even so, if we want to describe its effects, we have to be careful about our point of view. It is a particularly complicated issue, so we’ll treat it with a light touch here. In our case we’re interested in a process known as time dilation, another relativistic effect. The gravity of the black hole warps spacetime itself. (By the way, I’m happy enough to make all of these assumptions, but it is worth noting how many we’re making just so the ‘ordinary’ mechanics of a black hole don’t destroy us!) In fact, let’s assume you’re falling into an otherwise entirely quiet black hole and there are no jets or an accretion disc. You have enough to worry about, so let’s assume the jets aren’t a problem. Significantly, they align with the axis of rotation, whereas we are approaching almost perpendicular to it in the accretion disc. They’re also complicated things with unanswered questions surrounding them, so we won’t dwell on them too much. Jet beams may extend millions of light years, so hopefully we would have noticed them before now. The black hole may even produce tightly focused astrophysical jets of ionised matter (sufficiently powerful and with velocities high enough to be referred to as relativistic jets). The result is highly energetic radiation, including things like powerful x-rays. As we’ve seen, the accretion disc formed emits radiation due to this friction and, because of the immensity of the gravitational pull, particles are accelerated up to significant fractions of the speed of light. Unfortunately, other stuff seems to be falling into our black hole too.Īlthough a bit of company might seem welcome, infalling particles spiral into the black hole in a turbulent flow, rubbing up against each other. Again, this is not to say that the gravitational pull isn’t strong, just that the gradient isn’t too extreme. Black holes of different masses will have different gradients, so with supermassive black holes it is perfectly possible to pass the event horizon with no ill-effect. But in extreme situations the tidal forces will pull you apart, a process known as spaghettification. You’re beginning to stretch, resisting that stretch by the strength of the material making up your spacecraft. The gravitational gradient as you get closer to the black hole is increasingly steep, so the difference between the gravitational pull on the parts of the spacecraft nearer the black hole and those further away grows. The space station is literally receiving different wavelengths than you’re transmitting, but while I’m busy retuning the receivers, you’re becoming ever more worried about the tidal forces acting on the spaceship. Realistically, what can I do?Īs you get closer to the black hole, the signals you’re sending are undergoing increased gravitational redshift as the photons climb out of the gravitational well. It’s probably time to start signalling for help, so you send a radio signal to the distant space station from where I’m observing things as best I can. You haven’t even reached the weird stuff – this is fairly conventional mechanics – though already you might realise you’re in trouble. Because the disc is flat, moving around what you’re going to think of as the equator of the black hole, you might try to get yourself ‘above’ or ‘below’ the disc, but you’ll be pulled back into alignment.
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