Register to reply 
Black hole anatomy 
Share this thread: 
#19
Mar512, 03:03 AM

P: 124

I understand pressure is required to supports a balloons surface but not so simple on a bowling ball. Why is pressure needed on a complely solid object?



#20
Mar512, 04:48 AM

Sci Advisor
P: 4,835




#21
Mar512, 08:26 AM

P: 1,261




#22
Mar512, 10:59 AM

Sci Advisor
P: 4,835

From the point of view of the outside observer, an infalling object actually never crosses the event horizon. In fact, Hawking radiation causes the black hole to become smaller before the infalling object ever reaches it. So, what happens to the object if it is never allowed to even cross the event horizon? Note that if we accept classical General Relativity, from the point of view of the infalling object, it does crash into the singularity in finite time. And this is also what happens even if the black hole is an evaporating black hole that has always existed. Last time I looked this up, however, nobody had managed to figure out what happens in a black hole that forms and evaporates in finite time with General Relativity. Finally, consider that the Hawking Radiation encodes the information of whatever fell into the black hole, so that the radiation which leaves is physically connected to matter that entered into the black hole. So my supposition is that the black hole can actually be seen as sort of a collision of matter occurring with an extreme amount of time dilation that is so destructive that it almost perfectly thermalizes any and all matter which enters the collision. This is, however, just supposition. 


#23
Mar512, 11:03 AM

P: 124




#24
Mar512, 11:33 AM

Sci Advisor
P: 4,835




#25
Mar512, 12:59 PM

P: 124

Sorry, I am not trying to beat a dead horse here but I am talking about after neutron degeneracy pressure of the neutron star and any other stages of collapse a body of mass may go through including the stage of converting to a black hole. Which I think is the same as all the other stages where the escape velocity just rises another notch. In this case it rises above the speed of light. But after that stage what stages are there and eventually you get to a particle that are so much smaller than anything else. There would be no other place to collapse to.



#26
Mar512, 01:05 PM

Sci Advisor
P: 4,835




#28
Mar512, 01:27 PM

Sci Advisor
P: 4,835




#29
Mar512, 01:31 PM

P: 1,261

Second, the same argument would apply to the classic undergrad question 'how does the blackhole increase in mass at all?'  which is a nonissue. The object crosses the event horizon without a problem, its just never observed. 


#30
Mar512, 01:34 PM

P: 1,261




#31
Mar512, 01:36 PM

Sci Advisor
P: 4,835

And yeah, obviously I was talking about a semiclassical black hole with regard to evaporation, which uses General Relativity to define the spacetime but adds an evaporation mechanism. 


#32
Mar512, 01:44 PM

P: 1,261




#33
Mar512, 01:52 PM

Sci Advisor
P: 4,835




#34
Mar512, 01:53 PM

P: 728




#35
Mar512, 01:59 PM

Sci Advisor
P: 4,835

Edit: Of course, this almost certainly isn't enough to produce a degenerate bosonic state at the center of a black hole, because you also have to get rid of the baryons, and baryon number is a conserved quantity in known physics. So we would probably need some beyondstandardmodel interactions to get into a degenerate bosonic state, and that may open the door for still more bosons. 


#36
Mar512, 01:59 PM

P: 1,261

It was specifically in reference to your comment that:
But going back to the initial point; the event horizon can definitely form stably. We agree that the singularity itself is completely questionableso that part doesn't really matter. My overall argument is that we are really really confident event horizons can form; and quantum mechanics (string theory etc etc) only suggest GR breaks something like 50 orders of magnitude closer to the center of the BH than the event horizon... so there doesn't seem to be a reason to expect GR to break near the EH... (Unless you're looking at a nearextremal kerr blackholewhich we believe existin which case the singularity itself can be very near the event horizon. 


Register to reply 
Related Discussions  
Relativistic mass increase appearing to form a black hole vs. a real black hole  Special & General Relativity  9  
Time dilation and blackholeblackhole mergers, and ringdown gravitational waves  Special & General Relativity  13  
Is it possible to escape a black hole's event horizon in a binary black hole system  Astronomy & Astrophysics  6  
Will a black hole revolve around a nonblack hole object with greater mass?  General Physics  2 