Squish

When discussing time dilation near Black Holes one normally refers to “local” time at the event horizon and remote time or “coordinate” time as experienced by a remote observer stationary relative the BH. But time dilation increases steadily as one approaches a Black Hole. For example, if the Black Hole event horizon radius is 1 million kilometers, then 1 kilometer away from the horizon the time dilation rate would be 1000:1 relative to coordinate time. At 1mm away it would be 1,000,000:1. It shoots up to infinity as one approaches the horizon. There is relative time dilation between any two places at different distances from the Black Hole.If you were falling feet first into a Black Hole, then as you approached the event horizon your feet would be very time dilated and slow down relative to your head. Your head would catch up with your feet and you would be concertinaed, go “squish”, and arrive at the event horizon as a thin pancake. In fact this would happen so fast that you would go “splat” as you pass through the event horizon. Of course the Black Hole would inevitably be rotating and would turn the splat into a smear. But for us distant observers, if we could make any observations that close to the event horizon, it would be a slow squish.This applies to any cloud of matter falling in. Leading particles would slow down relative to those further out, and in their local time they would all arrive together. However this is not quite true for a large mass because its trailing edge would slowly approach a new event horizon forming further out due to the added mass.All calculations for stellar collapse and for objects falling into Black Holes have ignored pressure in the collapsing medium. But with large amounts of matter falling into a Black Hole and “squishing”, pressure becomes an important factor. The pressure of the squish would force matter out sideways, but with matter falling in all around the equatorial regions of a Black Hole it has nowhere to go except out towards the poles. The extreme pressure would force a jet stream of matter poleward at tremendous speed (relativistic?) where it would all collide creating a jet of matter spewing outwards into space. I propose this as the mechanism behind the jet emissions observed in AGN galaxies, emitted by their central Black Holes.Now I just need some mathematical genius to do the Black Hole calculations taking pressure into account. Modern computers should help.I have had fun with my descriptive terms “squish”, “pancake”, etc, but I am sure there must be technical terms for these conditions, probably in the field of hydraulics.

Thread copied here from the Squish thread in the Proposed New Topics forum.

I thought that nothing...not even light...could escape once the event horison was passed. So wouldnt the squished substance stay trapped in the black hole rather than oozing out the "sides"?

I might misunderstand what you're saying, but I think it's that as a large mass approaches a black hole that the black hole's event horizon gradually expands toward that mass. Do I have that right?If so, then this seems wrong. Consider the case where the large mass is actually a very, very large mass, i.e., another black hole of similar size. As the two black holes approach each other their mutual event horizons closest to the other will retreat toward their mutual centers. This is because the point midway between the black holes is a point of zero gravity (they cancel each other out). When their event horizons eventually "meet" they won't actually be at the midpoint anymore, having retreated some distance away.If that's correct then when a large mass, but not so large as to be a black hole, approaches a black then the black hole's event horizon will retreat away. If the large mass is considerably smaller than the black hole then the retreat will be negligible, but if it's a truly large mass such as a star then it should be measurable.Perhaps you were thinking that the gravity of the large mass would exert an attractive force on the event horizon. It can't do that because the event horizon isn't an actual object upon which gravity can exert a force. It's conceptual. The concept is very real, and there is matter at the event horizon (or at least so our current theoretical understanding posits), but as an actual thing consisting of matter it is not real.Interestingly, this case is where the "bowling ball on a trampoline" analogy breaks down. As two bowling balls on a trampoline approach each other the depression at the midpoint between them becomes greater rather than lesser.--Percy

The phenomena that occur as matter approaches a black hole are bizarre in the extreme, but why would the squish/splat happen precisely at the event horizon?I have seen astrophysicists discuss the distortion of spacetime being so extreme around a black hole that the difference in tidal forces between your feet and head would stretch you out or "spagettify" you.I know saying something doesn't make sense around a black hole, but nothing makes sense around a black hole, so it doesn't make sense to me that matter stops at the event horizon. It seems to me that matter would continue falling inward until it gets to the center, but I would also expect that all the matter would be converted to energy at some point in the process, so maybe everything inside the event horizon is a seething caldron of pure energy.Outside of black holes, out here in the Universe we can observe we think the densest objects are neutron stars. When enough mass is added to a neutron star it becomes a black hole, but does that mean that there is still a neutron star inside the event horizon or has the neutron star transitioned into an even denser more compact form?

Of course nothing takes place at the event horizon, at least as far as we distant observers are concerned. I envisage all this "squish" taking place a little distance outside the black hole. A lot of the matter squished out towards the poles would fall into the Black Hole before it got there, but the matter that did get there would collide with terrific force.

When a mass falls into a Black Hole, there is a Schwarzschild radius defined by the combined mass, and that radius only becomes an event horizon once all the incoming mass has fallen inside it. But due to time dilation the outer layers of that mass will approach the Schwarzschild radius asymptotically, forming a new event horizon after an infinite time.
I don't know how to copy a diagram into this reply, but it is illustrated perfectly in Liu and Zhang's "Exact solutions for shells collapsing towards an existing black hole", Physics letters 17/8/2009, in diagram 5b of that article.
Black holes merging is a little more complicated, but not relevant here.

Tasmypterix, It has been proposed that spaghettification might not take place as one falls in if the black hole is large enough and the gravity gradient more gradual. But I am suggesting that if the gravity doesn't get you, then the time dilation will. How these two opposite effects combine as one approaches the event horizon will depend on Black Hole size and your starting position and velocity. But the time dilation gradient goes to infinity at the event horizon, while the gravity gradient doesn't, so my squish effect will win out at the end.Regarding matter stopping at the event horizon, you have to get your head around the flow of time being different for different observers. Where there is mass, there is gravity, and where there is gravity time flows more slowly (relative to places with less gravity). But it is the gravity potential, not the force, that counts. Our clocks and all time here on Earth are slowed by Earth's gravity, and atomic clocks in GPS satellites up in orbit tick over a little faster than identical ones down here. NB. it all gets a bit more complicated when relative motion is also involved.Edited by Mike Holland, : Trying to avoid a future argument over a minor point..

Thanks, good answers and an interesting topic.

I'm not so sure. You are looking at a Kerr solution since the black hole is rotating. That means, IIRC, there is a hyper-photon sphere just outside the event horizon. Photons trapped in orbit about the black hole without falling in and without the momentum to escape. This, I would think, would give you a really nice instant tan before you are disintegrated into high energy plasma the next instant.As an observer I would expect to see you slow to imperceptibly slow motion as you very slowly burst into flame and are consumed, slowly, over days, as your pain contorted image fades into the far infrared. Though you would have to follow the image around as it too orbits the black hole at incredible speeds due to frame dragging.Under your time dilation scenario, by the time your head was ready to enter the splat zone, the rest of you has already been dissolved and has been dragged on while still millimeters off the event horizon. There is nothing there for the incoming new plasma to splat on.Maybe you were right. The slow, yet instant, flash of your being sublimated from person to plasma, sped across the scene around the orbit might very well look like a slow motion splat except this splat would soon span the entire orbit.To splat or not to splat? Too many variables.Edited by AZPaul3, : No reason given.

OK, I had to do a bit of reading on the event horizons there. I couldn't find any estimates on the photon density in this hyper-photon sphere, their energy spectrum, or their anticipated half-life there before they either escape or fall in. I also have a gut feeling that polar orbiting photons will be pulled into equatorial orbits by the space drag, so that the result will be a ring of fire rather than a wall of fire.Anyway, it seems my pancake will be smeared as it gets cooked. Depends of the relative rates of timed dilation and space drag as one approaches the event horizon(s).But in the case of large amounts of matter (stars, clouds of gas) falling into a supermassive Black Hole at the center of an AGN galaxy, I think the squish would start taking place much further out, and my explanation for the polar jets is still viable.

Except we have quite a viable set of explanations with at least some evidence of what relativistic jets are in actively feeding galactic nuclei. Incoming matter is ripped to its constituent particles and into huge electrically charged fields of plasma that are shunted to the axial jets by the super strong magnetic fields that surround the central black hole.Astrophysical jet - WikipediaIf you're into the hard details here is one treatment (detailed pdf):Page Not Found! : Department of Physics and Astronomy: Purdue UniversityYour explanation doesn't seem as complete. Magnetic moment seems a better motive force than just an undefined squish with polar squirting. God, I loved writing that.Anyway, I still don't see it, Mike.Edited by AZPaul3, : No reason given.

Edited by AZPaul3, : No reason given.

OK, thanks, Paul. I didn't know there was a fairly well developed theory about the jets. I thought they were still a mystery. So I will scrap my theory and read the references you supplied.
Cheers, Mike

Aren't tidal forces near a black hole so great that long before you reached the event horizon you would already be spaghettified? Consider the example of a fairly typical black hole of 10 solar masses, or 2*10³¹ kg. The radius of black holes follows a simple formula of R=3M, where M is the multiple of solar masses and R is in kilometers, yielding a radius for this black hole of 30 km. What would the difference in gravity be for an object 31 km distant from the black hole's center versus 31.002 km distant. .002 km is roughly the height of a man, so the question being asked is what is the difference in gravity between a man's head and feet a kilometer distant from the black hole's event horizon?Just doing the very simple, the ratio in gravity between the two distances only 2 meters apart is 1.00013, so close to 1 as to seem negligible.But it's not negligible because given the huge gravitational force .00013 of it must be enormous. The gravitational force a kilometer out from the event horizon is 6.67*10¹⁴ newtons, so .00013 of that is 8.67*10¹⁰ newtons, or translating it into something more familiar, something in the neighborhood of 20 billion pounds.A difference in gravitational pull of 20 billion pounds between head and toes would be far more than enough to spaghettify a person, so long before you ever reached the event horizon you would already be spaghettified.I don't have the background to take relativistic effects into account.--Percy

This is off-topic, but as Mike's doing some more investigating I thought I'd introduce a puzzler.Remember that old puzzler about the innkeeper who charges three men $30 for their room, $10 each, but later realizes he should only have charged them $25. He gives the bellhop $5 to bring to the men's room, but the bellhop realizes $5 doesn't divide neatly by 3 and pockets $2, giving $1 to each man. So each man paid $9 and the bellhop kept $2 for himself for a total of $29. What happened to the other dollar?This puzzle misleads its victims by structuring the question improperly, and I think I have the relativistic equivalent of this puzzlez.A kilometer long alien spacecraft is traveling perpendicular to us at .97c and so is perceived by us as only a quarter kilometer long (approximately). It passes behind a moon a half kilometer in diameter. When the spacecraft is centered behind the moon it will be completely hidden from us, but observers in the spacecraft's front and rear can clearly see us at the same time. They take pictures of our clocks. When we meet later and compare notes we discover that at the same time they could see us clearly from both ends of their spacecraft they were completely invisible to us. How is this possible?--Percy