A black hole is a volume from which photons, or any matter, can not escape. More formally, the coordinate speed of light at the event horizon - the boundary of a black hole - is zero, as measured by a sufficiently separated observer.
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Which way does a black hole spin?
As far as I understand, and from what I have been shown in renderings of black holes, they spin (like water going down a drain).
My question is, firstly, does the matter being pulled into a black
...
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4answers
203 views
Time inside a Black hole
If time stops inside a black hole, due to gravitational time dilation, how can it's life end after a very long time? If time doesn't pass inside a black hole, then an event to occur inside a black ...
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Anti-matter black hole and time
I have recently read some hard science-fiction story based on an assumption that if time stops (from external observer's perspective) on the event horizon of black hole, then in an anti-matter black ...
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Negatve mass inside a black hole
With Hawking radiation, one half of virtual pair falls into horizon and this particle has negative energy.
What would an observer inside horizon observe when seeing negative particles ?
How do these ...
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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 ...
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What is the strange event in this simulation of a galactic collision?
I was watching this video on YouTube: 2 Spiral Galaxies w/Supermassive Black Holes Collide
Around half way, and again almost at the end, the black holes seem to suddenly give off some sort of force ...
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Black Hole Singularities
If two black holes collide and then evaporate, do they leave behind two naked sigularities ore? If there are two, can we know how they interact?
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What is the color shift if light passes between two (or more) black holes?
If we observe light that originates X light years away, but it passes between black holes X/2 light years away, will it be normal or red shifted or blue shifted? What if the black holes were X/4 or ...
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Why does the Kruskal diagram extend to all 4 quadrants?
Why is it that the Kruskal diagram is always seen extended to all 4 quadrants when the definitions of the $U,V$ coordinates don't seem to suggest that the coordinates are not defined in, say, the 3rd ...
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159 views
What happens to the wavelength/frequency of a photon as it passes through an event horizon?
I've asked a similar question about photons and black holes but wanted to rephrase it more specifically, so here goes...
Ever since I learned how a photon's wavelength and frequency are indivisibly ...
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how does nature prevent transient toroidal event horizons?
.. and does it really need to?
Steps to construct a (transient) toroidal event horizon in a asymptotically flat Minkowski spacetime:
1) take a circle of radius $R$
2) take $N$ equidistant points in ...
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117 views
The role of dark matter in black holes and star formation
In my understanding, there exists a critical mass for which a star needs to be in order for it to collapse into a black hole. This also applies to a certain critical density of gas in order for stars ...
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Theoretical basis for black hole evaporation
What is the basis for black hole evaporation?
I understand that Hawking-radiation is emitted at the event horizon, a theoretical result originating in General Relativity and Quantum Field Theory, but ...
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Returning Light
What happen if someone is just close enough to a black hole, and he emits light tangentially out, and the light got bent and circles around, what will he see, can he see the light source from his ...
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Why don't black holes within a galaxy pull in the stars of the galaxy
visit http://www.nasa.gov/audience/forstudents/k-4/stories/what-is-a-black-hole-k4.html
If black holes can pull even light, why cant they pull the stars in the galaxy?
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What happens at the moment black hole is created?
Suppose a body has just enough matter in it that just 1 more electron could turn it into a blackhole. When this happens, where does all that matter go?
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Is the Schwarzschild black hole unphysical?
To obtain the Schwarzschild metric from Einstein equations of general relativity, we suppose that the energy density is a distribution :
$$ \rho (\vec{r}) = M \delta(\vec{r})$$
The Schwarzschild ...
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When a high speed neutrino just misses an old neutron star, why isn't it trapped?
Suppose a neutrino is seen travelling so fast that its Lorentz gamma factor is 100,000. It races past an old, no longer active neutron star, narrowly missing it. As far as the neutrino is concerned, ...
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Why doesn’t gravity break down in a large black hole?
By popular theory gravity didn’t exist at the start of the Big Bang, but came into existence some moments later. I think the other forces came into existence a little latter.
When a black hole ...
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Why are black holes special?
A black hole is where it's mass is great enough that light can't escape at a radius above the surface of the mass?
I've been told that strange things happen inside the event horizon such as ...
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1answer
86 views
Diving into a charged (Reissner-Nordstrom) Black hole
Apparently there are two event horizons in this type of black hole, where the second one is known as the Cauchy horizon. According to Carroll, if you go into the first one, you will fall until you ...
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1answer
94 views
Reconstruction of the initial state from Hawking radiation?
I hear that unitary evolution and information conservation must imply that information about information content that defines the initial state of matter used to create a black hole can be inferred ...
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2answers
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Future light cones inside black hole
In Caroll's Spacetime and Geometry, page 227, he says that from the Schwarzschild metric, you can see than from inside a black hole future events all lead to the singularity. He says you can see this ...
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What happens to atoms inside the black hole?
Black holes have very high gravitational force intending to crush everything. So as we know atoms in a molecule have inter atomic spacing between then and further electron,s also revolve at a certain ...
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A Conflict with Black Holes
If a particle with rest mass falls from r = infinity to r = Rs of a black hole it is supposed to reach a velocity of c. But where does all that energy (infinite) come from to bring the rest mass to a ...
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Gauss-Bonnet theorem in the Hawking/Ellis book
At the page 336 of Hawking, Ellis: The Large Scale Structure of Space-Time, the Gauss-Bonnet theorem is stated as
$$\int_H \hat{R}\ d\hat{S} = 2\pi \chi(H) \qquad (1)$$
with
$$\hat{R} = R_{abcd} ...
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Rotating Empty Sphere around stationary black hole
Would it be possible to create a habitable in terms of gravity planet that would rotate with the black hole acting as a center of gravity? The rotation of the structure would lessen the gravitational ...
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148 views
what does holographic principle from string theory say about the possibilities of wormhole travel?
Is travel through stable macroscopic wormholes between remote points of spacetime going to be possible in a definitive theory of gravity, be it string theory or something beyond it?
Physicists level ...
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139 views
Black hole entropy
Bekenstein and Hawking derived the expression for black hole entropy as,
$$
S_{BH}={c^3 A\over 4 G \hbar}.
$$
We know from the hindsight that entropy has statistical interpretation. It is a measure ...
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2answers
259 views
Hawking radiation from point of view of a falling observer
This paper tells that Hawking claimed that the falling to a black hole observer will not detect any radiation. But only because the frequency of the Hawking radiation will be of the order $1/R_s$ so ...
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140 views
Can a charged black hole interact via electromagnetism? [duplicate]
Possible Duplicate:
Detection of the Electric Charge of a Black Hole
Light cannot escape from a black hole. However light is also interpreted as the carrier of the electromagnetic force. So ...
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2answers
87 views
Galaxies Center
It is believed (to my understanding) that at the center of all large galaxies are super massive black holes. Why is it then when you see photos of galaxies that the center is extremely bright if a ...
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1answer
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Kerr-Newman black holes and infinite charge
Recall the first law of BH thermodynamics
$ dM=\frac{\kappa}{8\pi} dA + \Omega dJ + \Phi dQ $
Now, let's consider the Reissner-Nordstrom solution $J=0$ such that $m>Q$ but only slightly greater. ...
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Black hole related questions
Well I have a couple of questions regarding Black holes so here they are,
1.Shouldn't they be called black spheres?(holes are in 2D right?)
2.What will happen if black holes collide?(If they can)
...
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1answer
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Notational(?) Question in Whiting's Paper “Mode Stability of the Kerr Black Hole”
I am a math grad student attempting to read Bernard Whiting's paper "Mode Stability of the Kerr Black Hole." If you are in a university network, the paper should be easily found by a google search. At ...
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1answer
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“WLOG” re Schwarzschild geodesics
Why, when studying geodesics in the Schwarzschild metric, one can WLOG set
$$\theta=\frac{\pi}{2}$$
to be equatorial? I assume it is so because when digging around the internet, most references seem ...
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1answer
59 views
An infalling object in a black hole looks “paused” for a far away observer, for how long?
As I understand, to an observer well outside a black hole, anything going towards it will appear to slow down, and eventually come to a halt, never even touching the event horizon.
What happens if ...
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1answer
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Killing Vectors of BTZ black hole and their calculation in general
I was wondering what are the Killing vectors of BTZ black hole and how to guess them easily? Will it be the same as of AdS? What then will be Killing vectors for AdS-Schwarzschild e.g.?
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1answer
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Would dense matter around a black hole event horizon eventually form a secondary black hole? [duplicate]
Possible Duplicate:
Black hole formation as seen by a distant observer
Given that matter can never cross the event horizon of a black hole (from an external observer point of view), if a ...
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1answer
138 views
is this generalized Hawking radiation formula right?
Look at equation 11.2.17 in this page. The expression is:
$$ T = 10^{-5} \text{K m} \frac{\xi}{\frac{GM}{c^2} \lbrace \frac{GM}{c^2} + \xi \rbrace - e^2 }$$
where
$$ \xi = (r_s^2 - a^2 - ...
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1answer
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Why doesn't the firewall argument also apply to far away ingoing modes?
Gidom Mera's answer at http://physics.stackexchange.com/a/45511 is illuminating, but on closer analysis, it brings up further puzzles.
Backscattering works in both directions. Let's see what we get ...
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1answer
94 views
Angular momentum of a rotating black hole
Is there an upper limit to the angular momentum of a rotating (Kerr) black hole?
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1answer
199 views
black hole event horizon
Given gravitational time dilation, under what conditions will a test particle cross an event horizon before the black hole evaporates? Assume zero background radiation.
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event horizons are untraversable by observers far from the collapse?
Consider this a followup question of this one
In the classical schwarszchild solution with an eternal black hole, the user falls through the event horizon in finite local time, but this event does ...
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1answer
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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, ...
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1answer
239 views
Quantum phenomena near black hole event horizon
I wanted to re-open the question of quantum measurements across event horizons. If I set up two slits or more generally a diffraction grating which crosses a black hole event horizon, and I shoot a ...
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0answers
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Entanglement and Black holes
If you have two entangled quantum states, One state falls into a black hole and you measure the other state, What can you say about the state that has fallen into the black hole?
If you have billions ...
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1answer
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Relativistic Computation?
Is it possible to employ relativity to develop computational technology?
Here is a really basic example:
Build a Computer and Feed it the Problem (say the problem is projected to take 10 years to ...
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0answers
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What happens when one black hole eats another black hole? [duplicate]
Everyone seems to know about black holes. They have an absolutely massive mass, and if you go into them, time stops from an outside perspective.
When a planet gets too close to a black hole, it is ...
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Falling into a black hole emitter vs observer
Let's say we are working with the Schwarzschild metric and we have an emitter of light falling into a Schwarzschild black hole.
Suppose we define the quantity $$u=t- v$$ where $$dv/dr= ...
