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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Newman-Janis algorithm (Schwarzschild to Kerr metric)

my question is how to find the null tetrad for the Schwarzschild metric in Eddington-Finkelstein coordinate? pic 1: I only get the last two values but not able to find the first two tetrad values ...
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Is it possible for a particle to orbit a singularity inside the event horizon [duplicate]

Event horizon just means a distance from singularity, where there is no "going-away" from the black hole. But is it possible, that there are particles with enough momentum to actually orbit the ...
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How would one attach black hole to starship in the Black hole Starship model? [on hold]

A black hole starship is a theoretical idea for enabling interstellar travel by propelling a starship by creating an artificial black hole and using a parabolic reflector to reflect its Hawking ...
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Rotation of Spacetime $\Rightarrow$ Change in orbit/path

Along the idea of frame-dragging; Will the rotation of a black hole, which has some velocity v and angular momentum, influence its path in 3D space? I've seen the fact that depending on the ...
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Energy conservation around a black hole

In the Schwarzschild black hole, the Killing vector "time translation" $k^a$, so that the following quantity is conserved along a geodesic: $$E = -g_{ab}k^au^b = (1 - ...
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What happens if I slowly lower a dangling object into a black hole?

I could've sworn I've seen this question before, but I couldn't find it. Suppose I have an object on the end of a really long string. I can slowly lower it near the event horizon of a black hole, ...
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Why does imaginary periodic time of the Rindler space of black hole give Hawking temperature?

The metric of a Schwarzschild black hole in Rindler coordinates is $$ds^2= -\frac{\rho^2}{(4MG)^2} dt^2 +d\rho^2 + d\mathbf x_\perp$$ where $\rho$ gives us the distance to the horizon. If we switch ...
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Can a black hole have negative temperature?

Stephen Hawking said that black hole also have temperature and it is related to its mass so in other words a black hole can also be shown to have a negative temperature! I know that nothing is colder ...
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Does a black hole ever fully form to an outside observer? [duplicate]

According to general relativity, I had understood that time appears to slow down when looking into high gravitational fields from afar, so that as a black hole forms, the light from a collapsing star ...
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Could dark energy and Hawking radiation be the same thing? [on hold]

Specifically, could black holes effectively emit some kind of negative mass or other form of dark energy, so that the mass of the black hole itself would actually increase rather than decrease ...
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Interpretation of black-hole infalling and apparent geometry of the event horizons

Consider a citizen of the cosmos crosses the event horizons of a black hole. For sake of discussion let's suppose is a Kerr black hole, so that his fate is not sealed the moment he crosses. Does at ...
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An explanation of Hawking Radiation

Could someone please provide an explanation for the origin of Hawking Radiation? (Ideally someone who I have been speaking with on the h-bar) Any advanced maths beyond basic calculus will most ...
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Another layman blackhole question, pulling one end of a string out from behind the event horizon

No long explanation is needed, What would happen if I were to allow one end of a rope to fall past the event horizon of a black hole while I held the other end? Would I be able to pull it out? Would ...
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Equilibrium for a rope hanging in a Schwarzschild spacetime

Update: Trimok and MBN helped me solve most of my confusion. However, there is still an extra term $-(2/r)T$ in the final result. Brown doesn't write this term, and it seems physically wrong. Update ...
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What will happen to Earth if it's tied to a black hole thru a really strong string?

Imagine a very strong string (with infinity as as its breaking point) attached to earth very strongly and the other end is put inside a black hole, What will happen to Earth? And the string? Will ...
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Could a black hole maintain a stable orbit around the Earth?

Could a rotating Black Hole of mass $1.24\times 10^{10}$ kg maintain a stable orbit around Earth, without significantly altering the path of the Earth or Moon? In addition to this, would the presence ...
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Can the density of a black hole be altered (if at all) by absorption? [on hold]

If a black hole is an object of sufficient density that it distorts spacetime, when a black hole absorbs mass, does the dense material that constitutes the black hole become less dense if the absorbed ...
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How do we know the Schwarzschild solution contains an object of mass $M$?

The Schwarzschild metric is $$ds^2 = - \left( 1 - \frac{2GM}{r} \right) dt^2 + \left(1-\frac{2GM}{r}\right)^{-1} dr^2 + r^2 d\Omega^2.$$ In Carroll's GR book, it is claimed that $M$ is the mass of the ...
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A doubt regarding Black Hole Complementarity

A friend was explaining Black Hole Complementarity to me, and at one point he said that to get a (horrendously) mixed quantum state, i.e. a thermal density matrix without a heat bath, one takes a ...
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Why would a black hole evaporate? [duplicate]

Hawking radiation doesn't make sense to me, with respect to black holes getting smaller. It would seem that any particle (or anti-particle) leaving the Schwartzchild radius would have a similar ...
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49 views

Pair Production via Black Hole

I think this should be a straight forward question. Is it possible for a photon to pass near a black hole and be turned into a matter and anti-matter pair according to current theory? Edit: From the ...
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Utilising Black Holes as a potential energy source

I'm aware of the Penrose process and the basic physics behind that. Also, I know that the Blandford-Zjanek process (That is potentially responsible for the relativistic jets). Aside from these two, ...
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Are black holes hollow? [closed]

So when enough matter to create a black hole falls towards the center of its collective mass, at one point the mass/area ratio becomes high enough to form the event horizon of the black hole. Because ...
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Non equilibrium black hole radiating away energy and angular momentum, with total energy and angular momentum conserved

The question refers to whether mass (i.e., energy) and angular momentum can be considered to have been carried away by the gravitational radiation in the hole settling down. And whether those entities ...
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Black hole gravity vs parent star gravity

In the cases of black holes that form from supernova and collapse of a massive star, I understand that in most of these cases, the star loses significant amounts of mass from the explosion. ...
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Doesn't the Schwarzschild metric combined with Hawking radiation imply that nothing ever gets past the event horizon of a black hole?

According to the General Theory of Relativity, the coordinate time distance per spacetime distance traveled by a particle freely falling into a black hole gets closer and closer to $0$ as the particle ...
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Big Bang not really the beginning of a completely new universe? [closed]

From what I know about the origins of the universe and the big bang, it is stated that it all started from an intensely hot and dense mass. This sounds like a singularity to me, which means a black ...
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How can super massive black holes have a lower density than water?

I heard on a podcast recently that the supermassive black holes at the centre of some galaxies could have densities less than water, so in theory, they could float on the substance they were gobbling ...
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How can black holes be so dense?

It is said that if the Earth were a black hole, it would be the size of a peanut!? How is this density possible, are atoms really that sparse that they can be compressed so tightly? Is there some ...
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Binary black hole merger viewed from inside the event horizon

How did the metric evolve inside the event horizons of the black holes whose merger caused the GW150914 signal? In principle the Schwarzchild metric of a non-rotating black hole is known inside the ...
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2answers
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Is this analogy of Hawking Radiation correct?

Through reading of textbooks and other research papers, I have settled on the analogy of hawking radiation below (Written completely by myself) Within the ergosphere of the black hole, virtual ...
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If Black Holes Consume Space What Is The Space Traversing? [duplicate]

I've heard it stated by physicists that space moves into (Or through/down into if you like) black holes faster than the speed of light and that this is possible because the speed of light is a ...
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If black hole is a “hole”, how can its position be pinpointed from every position in universe? [closed]

Ok, this is going to sound lame but, here goes: When we say that a black hole is situated at a distance of 1 light year(let) FROM EARTH, that means it may situated at a distance of 100 light years ...
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Eddington-Finkelstein coordinate

The Eddington-Finkelstein coordinates in case of Schwarzschild metric are defined as \begin{align} u&=t-r^*\\ v&=t+r^* \end{align} where $$r^*=r+2GM\ln\left|\frac{r}{2GM}-1\right|$$ The ...
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Gravitational waves from neutron star - neutron star merger

How is neutron star-neutron star merger different from Black Hole-Black Hole merger and what information can be extracted from gravitational waves emitted by these processes?
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what is the metric of N-sheeted $AdS_3$?

Suppose the AdS$_3$ metric is given by $$ ds^2 =d\rho^2+cosh^2\rho d\psi^2 +sinh^2 \rho d\phi^2 $$ what is the n-sheeted space of it? Can the n-sheeted BTZ be constructed from it by identifications ...
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Can electrons escape a black hole?

Assuming that when an electron that changes energy states in an atom, and moves to a different orbit around the nucleus, but does not move through the space between orbits when it changes states, an ...
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Is force exerted by Earth different for different mass?

We know Earth pulls every object by the same acceleration $g$ (say). force exerted by earth $F=m\cdot g$ (with $m$ the mass of the body), so, if $g$ is constant then $F$ is directly proportional to ...
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Quarks falling in a black hole?

All I know about quarks is that they make up protons and neutrons and you can't really pull a quark pair apart, you just end up with 2 quark pairs because of all the energy you added becomes 2 new ...
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1answer
188 views

How does Hawking radiation grow as a black hole evaporates?

The temperature of Hawking radiation is inversely proportional to the mass of a black hole, $T_{\rm H}\propto M_{\rm BH}^{-1}$, and so as the black hole shrinks the temperature of the radiation should ...
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Based on our current observations, what all prevents a formed black from experiencing a repulsive force to overcome its gravitational force…?

Edit: I don't think this is a duplicate. [***] Question: Based on our current observations, what prevents a black from experiencing any sort of repulsive force to overcome its gravitational force ...
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Where does the energy of a photon trying to escape a black hole go?

I've heard "light cannot escape a black hole" explained several ways. One is that if a photon inside the event horizon tries to escape a black hole it loses energy to gravity. As it loses energy its ...
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How are negative energy orbits around a Black Hole defined?

I have read several times that within the ergosphere or a Kerr Black Hole, it is possible to have particles that have an orbital energy value of less than 0. However, I do not understand the concept ...
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What effect would a singularity have on the fabric of space time?

Galaxies are always moving and it seems that there are SMBHs at the heart of most galaxies. If black holes actually twist up spacetime so much thru infinite density how do we know that after the ...
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1answer
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If an object has a temperature, does it have to radiate?

I'm reading through a powerpoint presentation about Hawking Radiation (HR). They are explaining all of the reasons that built up to the postulate of HR, and one of the reasons is that if there is a ...
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Can tachyons escape the gravitational pull of a classical black hole?

Anything that crosses the event horizon of a black hole cannot escape the pull since it has crossed the Schwarzschild radius and thus, the escape velocity is greater than the speed of light, and since ...
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If one flies by the sun at .9999999c, will it become a black hole? [duplicate]

If one flies by the sun at .9999999c, will it become a black hole? If one flies by the sun at .9999999c, its width will become tiny due to relativistic contraction, while its mass will augment ...
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Is the LHC more dangerous if it works with more luminosity? [duplicate]

We've seen the restart of the LHC the last year, there were many rumors about the high-energy collisions at 13 Tev, there were some theories about black holes at 11 Tev or 9 Tev if there were other ...
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In the big crunch theory, when the big crunch singularity forms, can the resulting black hole decay through hawking's radiation?

I've been pondering about this and I couldn't really find the answer for this. The big crunch theory postulates that the universe will eventually stop expanding and reverse back in on its self into a ...
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Israel-Wilson-Perjés Solutions

I'm searching for a reference that gives explicitly the field strength (or at least the gauge fields) of the Israel-Wilson-Perjés Solution, using complex harmonic functions for the metric. In ...