Tagged Questions
0
votes
0answers
23 views
Spherically-symmetric Pressure free Collapse [closed]
How to show-"zero pressure and spherical symmetry implies that a point on the surface follows a radial timelike geodesic"?
0
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1answer
135 views
Do all black holes spin in the same direction?
My question is as stated above, do all black holes spin the same direction?
To my knowledge, the spin in the direction of the spin of the matter that created them. Another similar question was asked ...
53
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7answers
3k views
How can a black hole produce sound?
I was reading this article from NASA -- it's NASA -- and literally found myself perplexed. The article describes the discovery that black holes emit a "note" that has physical ramifications on the ...
4
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2answers
81 views
What reason(s) exist to suppose that all degeneracy pressures can be overcome in Black-Hole formation?
In models of stellar collapse to a black hole, it is a given that density increases without bound towards a singularity. Electron degeneracy I get. Neutron degeneracy I get. I assume there's some ...
5
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2answers
225 views
Do black holes have infinite areas and volumes?
How to calculate the area / volume of a black hole?
Is there a corresponding mathmetical function such as rotating 1/x around the x-axis or likewise to find the volume?
4
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1answer
89 views
NGCC 1277— a recoil ejection?
Recent calculations agree that a merging pair of supermassive black holes can emit enough gravitational waves to eject themselves from a galaxy.
Could NGCC 1277, a small galaxy with a 17 billion ...
4
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2answers
174 views
Does the Chandrasekhar Limit scale for a Black Hole?
No physicist/astrophysicist I; All I know about the Chandrasekhar limit is that it apparently limits the mass a star may survive, beyond which it degenerates to a neutron star, or a black-hole.
Does ...
0
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2answers
69 views
A thought about Quasars
If Quasars are "beams" of energy exiting a super-massive black hole, in order for them to get through the black-hole's event horizon, they'd have to be traveling faster than the speed of light. My ...
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4answers
109 views
How do black holes accrete mass?
Thanks to time dilation, a distant observer watching a man fall in to a black hole will only see him asymptotically approach the event horizon. So how do black holes ever get bigger?
3
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1answer
144 views
Why are black hole singularities stable?
The Friedmann equations says that huge matter densities lead to huge expansion rates. In Newtonian gravity, two massive point particles separated by an infinitesimal distance will experience an ...
8
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2answers
506 views
What is the physical size of a black hole?
Something that's always confused me. How large is a black hole's physical size - not mass?
From descriptions, it would seem that the 'singularity' is a single point, but is it really?
Say for ...
2
votes
1answer
90 views
When would the proposed black hole at the centre of Milky Way gulp in our solar system?
I've heard and read that our solar system lies near to the peripheral region of the Galaxy. Then accordingly we would have a greater probability of sustaining to eventual gulping down by the ...
5
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1answer
169 views
Why do the stars in the galaxy core move so fast?
There are a bunch of stars orbiting the black hole in the center of our galaxy.
These stars move at huge speed. Why do we see this? Why do the black hole not impose any noticeable time dilation on ...
1
vote
1answer
324 views
Blandford-Znajek process: Why/how does the current flow along the magnetic field lines
Related: How would a black hole power plant work?
I have put a bit of commentary enumerating my confusions in parentheses
I read in Black Holes and Time Warps (Kip Thorne), that quasars can generate ...
6
votes
2answers
186 views
Black hole collision and the event horizon
Will the event horizons of a two black holes be perturbed or bent before a collision? What will the shape of the event horizon appear to be immediately after first contact?
3
votes
1answer
146 views
Why can't a stable star have radius 1 < r < 9/8 its Schwarzschild radius?
From http://www.spacetimetravel.org/ssm/ssm.html :
A mass of 1.78 [in geometric units] corresponds to a ratio of radius to Schwarzschild radius of 9/8. Theory predicts that a smaller ratio is not ...
1
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1answer
150 views
Supermassive Black Holes = expansion origin?
(Sorry, couldn't resist the title)
An article on Physics Today brings news that there is a new record for largest black hole (not) seen in space, some 300 million light-years away. It hints at ...
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5answers
715 views
Anti-Matter Black Holes
Assuming for a second that there were a pocket of anti matter somewhere sufficiently large to form all the type of object we can see forming from normal matter - then one of these objects would be a ...
2
votes
1answer
16 views
Would the time dilation from being in low orbit around a black hole delay/slow the effects of quantum tunneling?
If quantum tunneling will cause rigid objects like rocks to rearrange their atoms into a slow-moving liquid-like state in ~10^65 years, could an object delay this fate through time dilation in a low, ...
6
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1answer
60 views
Where do the bipolar jets of black holes come from?
How are they formed? And why are they so bright?
8
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3answers
710 views
Can black holes actually merge?
If time stops at the event horizon, can we ever detect two black holes merging? In other words, if you are a short distance away, would you encounter a spherically symmetric gravitational field, or a ...
1
vote
1answer
441 views
Has Cosmological Natural Selection been disproved?
I've been reading Lee Smolin's Life of the Cosmos.
Great book and it makes a lot of sense that the conditions in black holes are the same as conditions at the big bang.
Question is, has his theory ...
5
votes
3answers
333 views
Black holes in a head-on collision
Assume two uncharged non-rotating black holes traveling straight at each other with no outside forces acting on the system. What is thought to happen to the kinetic energy of these two masses when ...
8
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3answers
465 views
Evidence for black hole event horizons
I know that there's a lot of evidence for extremely compact bodies. But is there any observation from which we can infer the existence of an actual horizon?
Even if we are able to someday resolve ...
2
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5answers
796 views
Is there a black hole in the centre of the Milky Way?
Is it true that the whole galaxy is actually revolving, and powered by a black hole?
Has it been proven, and if it is true, how can our solar systems actually keep up the momentum to withstand the ...
20
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6answers
2k views
How fast a (relatively) small black hole will consume the Earth?
This question appeared quite a time ago and was inspired, of course, by all the fuss around "LHC will destroy the Earth".
Consider a small black hole, that is somehow got inside the Earth. Under ...
8
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6answers
1k views
The final death of a black hole
What are the different death scenarios for a black hole? I know they can evaporate through Hawking radiation - but is there any other way? What if you just kept shoveling more and more mass and ...
