Can Matter Enter a Black Hole Intact? Debate & Advice

[MikeeMiracle]

TL;DR

Can anything enter a black hole intact

I am having a debate with someone who appears knowledgeable about black holes from the language he is using but we have a disagreement about if matter can enter a black hole. He is trying to tell me the gravitational gradient near the event horizon is such that spaghetification occurs as you approach the event horizon. I am debating that the spaghetification effect occurs near the singularity itself, not the event horizon.

I came to this understanding from reading posts on this forum that spaghetification will occur outside the event horizon for small black hole but for larger black holes the gravitational gradient outside the event horizon is not so great and that it would be possible for a human to cross the event horizon intact and alive.

I may have misinterpreted what I have been reading on here but can anyone offer some advise as to which one of us was correct.

Thanks

 

[PeroK]

Tell your friend to stick to cooking spaghetti, as he knows nothing about physics!

 

[Ibix]

You are correct. You could search for the "ouch radius" at PF for some details.

Note that the radiation environment outside most black holes would fry you anyway...

 

[PeterDonis]

I am debating that the spaghetification effect occurs near the singularity itself, not the event horizon.

You are correct. For a small enough hole, "close enough to the singularity" for spaghettification turns out to be at or around the horizon; but as the hole gets larger the "spaghettification point" moves further and further inside the horizon.

A simple heuristic to see the behavior is that the spacetime curvature of a black hole, which has to get sufficiently large for things like spaghettification to occur, is proportional to $M / r^3$, where $M$ is the mass of the hole. Since at the horizon, $r = 2M$, the spacetime curvature at the horizon is proportional to $M / (2M)^3 = 1 / 8 M^2$, i.e., it gets smaller as $M$ gets larger.

 

[DaveC426913]

Your friend is wrong. For a sufficiently large black hole - not only would you be able to cross the event horizon without deleterious effects on your personage - but it is so abstract a surface that you would have trouble detecting that you had crossed it at all - you'd have to calculate the location of the event horizon (using mass and distance measurements) to conclude you were passing through it.

 

[MikeeMiracle]

Thank you for the responses. He seemed to be obsessing over the escape velocity at the event horizon being the speed of light to which I was responding that just because the escape velocity is the speed of light that does not mean you need to travel at the speed of light to fall into a black hole which kicked off this debate. His response was:

"What I stated is that no positive mass density object can even reach a black hole. And what I further stated is that objects are attracted and/or pulled into the event horizon at or near the speed of light. And due to being drawn into a higher rate of acceleration, they disintegrate because there is a limit to what compounds can do to support their constituent structural integrity at a molecular and atomic level before they just fail. It is also called nuclear decay. So you are not trying to travel at the speed of light [which is impossible], you are being drawn into the gravitational current that is racing at the speed of light."

The above to me seems like he is not taking into account the IRF of the falling object and instead looking at the falling object as an observer to reach that conclusion.

As ever I am greatful to have this forum as a resource to cross check my understanding.

 

[Ibix]

What I stated is that no positive mass density object can even reach a black hole.

Wrong.

And what I further stated is that objects are attracted and/or pulled into the event horizon at or near the speed of light.

No. In any local frame the event horizon passes through you at the speed of light. This does not give any meaning to the notion that you pass through the event horizon at the speed of light.

The rest seems to be nonsense.