Conditions at an ultramassive black hole's event horizon

[Midphase]

Hello all,

 

I apologize in advance if this post is in the wrong section (hopefully not). I'm working on a story which was inspired in part by me wondering as to how could possibly Matthew McConaughey's character in the movie Interstellar be able to survive crossing into a black hole's event horizon without being destroyed far earlier and much further away from the event horizon by the extreme forces and heat present in the vicinity of a black hole (I know it's a movie, but I was given the impression that the filmmakers were trying to stay within the boundaries of science as much as possible). Upon reading Kip Thorne and Leonard Susskind's books on the subject, I learned to my surprise that a supermassive black hole's event horizon's tidal forces are well within a human's survival, with a tidal force differential being similar to what we experience on Earth.

 

So this got me thinking, what about an ultra massive black hole? Something between 30 to 50 billion solar masses? What conditions would exist within a few meters of the event horizon? Would, in effect, a person be able to observe (but not cross) the boundary of the event horizon from such a vicinity without being instantly disintegrated; or would other energy and heat make such a scenario impossible?

 

I hope someone here can enlighten me with as accurate science as possible about this particular question.

 

Many thanks!

 

>>Kays

[Lord Antares]

It depends on the size of the black hole. For supermassive black holes, the point where it would kill humans is (well) within the event horizon, whereas for small black holes, it is outside. This is because the distance from the center is important, rather than the distance from the event horizon. For supermassive black holes, the event horizon is much furhter away from the center and so the effect is weaker at that point.

 

So an ''ultra massive'' black hole would have even milder tidal effects on the event horizon than a supermassive one.

If you want a bit of mathematics, read this:

 

https://en.wikipedia.org/wiki/Spaghettification

[Midphase]

Thank you. Yes, I understand what you're saying regarding the tidal effects being mild due to the distance from the singularity. What I am curious about is if there are other forces present at the Schwarzschild radius which would make it difficult for a human to survive (well, beyond the vacuum of space) in a non-rotating black hole.

 

I realize that this is purely theoretical, but what I'm curious is if it would be possible (given the right mass of a black hole and the right circumstances) for a human being to come within a reasonable distance of (but not cross into) the event horizon and survive. I also assume that time dilation at such a proximity would very much be a factor.

[imatfaal]

Thank you. Yes, I understand what you're saying regarding the tidal effects being mild due to the distance from the singularity. What I am curious about is if there are other forces present at the Schwarzschild radius which would make it difficult for a human to survive (well, beyond the vacuum of space) in a non-rotating black hole.

 

I realize that this is purely theoretical, but what I'm curious is if it would be possible (given the right mass of a black hole and the right circumstances) for a human being to come within a reasonable distance of (but not cross into) the event horizon and survive. I also assume that time dilation at such a proximity would very much be a factor.

 

Time dilation is never a factor within your own frame - clocks within your own frame of reference run normally. But an outside observer would see you acting slower and slower - and would never actually see you cross the event horizon whilst you would calculate yourself sailing straight through without noticing any difference

[swansont]

We had a colloquium on the physics of Interstellar a few months back. As I recall, the radiation from the SMBH would fry you in very short order.

[Lord Antares]

We had a colloquium on the physics of Interstellar a few months back. As I recall, the radiation from the SMBH would fry you in very short order.

 

That's interesting, because the wiki article I linked says this:

 

 

While in the previous case objects would actually be destroyed and people killed by the heat, not the tidal forces, near a black hole (assuming that there is no nearby matter), objects would actually be destroyed and people killed by the tidal forces, because there is no radiation.

 

What is referred to as ''the previous case'' is that of a white dwarf and neutron star.

What is the deal here?

 

I always thought the radiation from black holes is very strong.

[imatfaal]

We had a colloquium on the physics of Interstellar a few months back. As I recall, the radiation from the SMBH would fry you in very short order.

 

I presume that is the radiation from the accretion disc rather than the hawking radiation. The hawking radiation from a super-massive blackhole is so low to be unmeasurable (many orders of magnitude cooler than intersteller void)

[swansont]

 

That's interesting, because the wiki article I linked says this:

 

 

What is referred to as ''the previous case'' is that of a white dwarf and neutron star.

What is the deal here?

 

I always thought the radiation from black holes is very strong.

 

"Assuming no matter nearby". Ironic to state that assumption, because AFAIK we generally notice black holes because of the radiation from infalling matter.

 

Edit: and not the case for Gargantua

[Strange]

It may have been a reference to the recent "firewall" hypothesis?

https://phys.org/news/2016-04-hot-problem-black-hole-firewalls.html

[MigL]

My impression was that Hawking radiation is a frame dependent effect, similar to Unruh radiation.

It is apparent to the faraway observer, but disappears for the local frame of the infalling observer, who is in unaccelerated free-fall.

However being stationary just outside the event horizon means an accelerated frame, and so there would be radiation ?

 

I'm not convinced myself and will have to do some research.

[imatfaal]

My impression was that Hawking radiation is a frame dependent effect, similar to Unruh radiation.

It is apparent to the faraway observer, but disappears for the local frame of the infalling observer, who is in unaccelerated free-fall.

However being stationary just outside the event horizon means an accelerated frame, and so there would be radiation ?

 

I'm not convinced myself and will have to do some research.

 

I think you are right that hawking radiation can be explained as unruh radiation for an observer in the accelerated frame holding outside an event horizon

[Mordred]

You also have Hawking-Berkenstein radiation generated by the magnetic generation of the accretion disk. Which is a different process than Hawking or Unruh radiation. The magnetic generation being due to interparticle interactions

 

The amount of gamma radiation of the accretion disk would be more problematic I would think however.

Edited April 12, 2017 by Mordred

[Midphase]

 

Time dilation is never a factor within your own frame - clocks within your own frame of reference run normally. But an outside observer would see you acting slower and slower - and would never actually see you cross the event horizon whilst you would calculate yourself sailing straight through without noticing any difference

 

 

Thank you for the clarification. Of course. I was thinking in terms of an outside observer looking at an object or other person approaching the event horizon.

 

My understanding is also that, to an observer moving toward the event horizon, the observer will always perceive the event horizon as being further away even after he has crossed it. I suppose yet another strange effect of being in a black hole.