Black hole thoughts

Great capture, that's on my to-do list of targets.  Part of the reason the jet is so prominent is because it is pointed towards us, the light approaching us is intensified because of relativistic beaming, the doppler effect essentially.  There are actually two equally powerful jets, one emitting from each side but the the one pointed away from Earth is visually absent.    You could say your image supports Einstein's theory of relativity

Uwe Deutermann:
when you approach a Black Hole at the Event Horizon the progress seen from an outside observer should be (is) infinite. I am ok with the fact that there is a Black Hole possible, but we should never see anything being swallowed in the rest of the universes lifetime.

It is right, we do not see the final swalloing. But the object approaching the event horizon will fade due to gravitational redshift (its getting darker the nearer it comes to the EH because the light loses energy by escaping the gravitational potential). So even if we could wait till infinity to see the object entering the EH, there would be nothing to see :-)

Uwe Deutermann:
if you could survive the entry, you would be instantly at the end of time (cannot even imagine what that could be)

I am not sure about this one, but i dont think you would be at the end of time - your personal timeline would not change, time would not run faster there than here for you. But if you could turn around and watch the universe while approaching the EH you would see something like a fast forward of the universes progress - if your eyes were capable of watching gamma ray, because all light would be blue shifted to a very high energy level :-)

Well, that gravitational monsters are mysterious. My mind is always blown away when i think about them - the same questions that you asked are often on my mind. In my second life i would be an astrophysicist to understand all these things

Hi Michael!

I believe that we see it the same way (btw, I studied Astrophysics, I am a life ahead of you ;-)). With the end of time I referred to the rest of the universe, looking back when you enter the Event Horizon. This is the "funny" part, you as the one who travels into the Black Hole will experience no change, while the rest of the universe is infinitely old. Infinite is a traumatic word in physics, not just time wise, also dense wise (Singularity). It usually points to a lack of understanding about the subject, that the models that we created are not sufficient. Everybody longs for the Grand Unified Theory (GUT) where those problems are eliminated (especially the Singularity). I see it way more fundamental: if infinite is such a bad thing, then the speed of light barrier and the Event Horizon are much "easier" targets to solve. And understanding that a person flying into a Black Hole will reach it "PAST" an infinite time does not make even sense.

 Kskostik,
I agree that Suesskind if one of the physicists who is on the right track, I would like to hear from him though that a collision/merge of 2 Black Holes should never be possible in the universes life time, hence the gravitational ripple effect to prove gravity waves senseless. Since I am pretty sure that all the physicists are smarter than I am I must miss again something, still wondering though what is missing. Your entropy question is really interesting, and I would not be surprised if there is a dodecahedral shape involved, if there IS a Black Hole at all that we can observe (see Saturns hex shaped storm at the North Pole!). But … is there even one visible at a stage that we can say it IS a Black Hole? Or are we just seeing always the close edge of an Event Horizon, never reaching the status of a Black Hole? This would very much look like a Black Hole, but still is not one (I am in favor of that one ;-)).

Uwe

Uwe,

Uwe Deutermann:
I agree that Suesskind if one of the physicists who is on the right track, I would like to hear from him though that a collision/merge of 2 Black Holes should never be possible in the universes life time, hence the gravitational ripple effect to prove gravity waves senseless.

Why is it so? Sorry, I am not getting it why 2 BH should not collide. Once I asked an astrophisicist a question: will we ever register a collision of 2 BH, since they are supposed to approach each other asymptotically? The answer was that BH merging equals merging of their horizons. Since horizons are not physical bodies, they should merge just fine without the asymptotic effect. The gravity waves we are registering are produced before the horizons merge. I guess, after the horizons merge, the BHs will continue to emit GW, which just don't leave the horizon.

There is a couple of interesting and controversial papers on super-massive BH, and their role in oscillating universe. Authors are claiming that both dark matter and observable acceleration of the universe expansion can be explained by general relativity without bringing in dark energy and exotic particles. I am very good in GR, and cannot say if there are any errors in their calculations. Perhaps, you can clarify.

https://arxiv.org/pdf/1608.01541.pdf

http://inspirehep.net/record/1666865/files/1804.02988.pdf

Uwe Deutermann:
But … is there even one visible at a stage that we can say it IS a Black Hole? Or are we just seeing always the close edge of an Event Horizon, never reaching the status of a Black Hole? This would very much look like a Black Hole, but still is not one (I am in favor of that one ;-)).

I guess, all we can say is that object's density has become high enough to form an event horizon. What exactly is happening to the collapsing object we cannot know, due to the horizon. Unless we learn to extract this information using something like quantum entanglement, which, apparently, preceeds space-time.

First of all apologies to John Michael, I did not want to move the topic to a more theoretical subject!

Here's one, if Saggitarious A* had relativistic matter jets like M87 shooting from it's poles would we be able to see them and if so what would they look like?

My gut feeling for this is that we would be able to see it in high energy wavelength, but not necessarily visually. I might be wrong on this one though.

kskostik,
Very interesting articles you refer to, I read the first one and beside the fact that it is very difficult to verify the equations (I remember them, but that does not mean I still can work with them, long time ago!) the conclusions are very interesting.

Michael Timm:
Once I asked an astrophisicist a question: will we ever register a collision of 2 BH, since they are supposed to approach each other asymptotically?

I like your question, since it is expressing my dilemma :-).

Michael Timm:
The answer was that BH merging equals merging of their horizons. Since horizons are not physical bodies, they should merge just fine without the asymptotic effect.

This looks like the answer, but isn't the horizon the point of (the asymptotic) problem? That gravitational waves can exist without a merge sounds reasonable, so I am ok with that. The merge itself is still a riddle to me (even the papers do not answer it). Maybe I need a simple answer which is not possible. I like simple and straight forward ;-), and nature usually is behaving that way.

Thank you all for an inspiring conversation!!

Uwe Deutermann:
My gut feeling for this is that we would be able to see it in high energy wavelength, but not necessarily visually. I might be wrong on this one though.

Hi there! The black hole in Sgr A* is not feeding very much. The vicinity of the BH is gas and dust-starved. There are stars whipping around it, but they don't go inside the roche limit. And there is that one gas streamer that was all a buzz in the news a few years ago. I haven't heard much on it since then. But I'm an astrophysicist. My dissertation was, in part, on BHs. They go through changes of state when they are accreting and the jets typically appear only in the low/hard state. This is when the accretion rate is low (but not so low that it's essentially zero). It needs to be accreting enough to have a prominent disk. It will have a truncation radius in the low/hard state and the jets result from magnetohydrodynamic phenomena occurring in the inner disk with the magnetic fields and strong BH rotation. These jets will produce copious amounts of synchrotron radiation peaking in the radio portion of the spectrum. This is such a significant portion of EM radiation from the jets that sometimes the low/hard state is even called the "radio loud" state!

I have a paper that deals with synchrotron radiation, but in the gamma-rays and in the context of pulsars...specifically the one powering the pulsar wind nebula associated with the Crab nebula.