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.

learn more… | top users | synonyms

-1
votes
0answers
32 views

Gedanken experiment: Does it collapse to a black hole or not? [duplicate]

Imagine that I am a stationary far-off observer of a massive star that is minutely larger than its Schwarzschild radius (in other words, its on the verge of collapsing). My spacecraft accelerates ...
-1
votes
0answers
16 views

Black holes – Irrotational vortex or Rigid-body-like vortex

As light enters a Black hole – does the light enter as “Irrotational vortex” or as “Rigid-body-like vortex”? https://en.wikipedia.org/wiki/Vorticity Thank You
1
vote
1answer
49 views

Mass and Schwarzschild Radius [duplicate]

Do free massless particles have a Schwarzschild radius? I'm curious about the mass in the equation for the Schwarzschild radius. I know that you can calculate a Schwarzschild radius for any massive ...
2
votes
4answers
172 views

Is a black hole's mass uniformly distributed?

If you were to fly around a black hole, would the gravitational pull be uniform and centered on the singularity, regardless of your relative location? If yes, how can this be consistent with models ...
1
vote
0answers
25 views

Short Gamma Ray Bursts from black hole mergers

I have read in passing that short gamma ray bursts can be caused by the merger of 2 black holes in a binary system. I have Googled but can't seem to find any good sources describing the phenomenon ...
-2
votes
0answers
52 views

Black-hole meets Black-hole [duplicate]

What will happen if a black hole collides with another black hole of equal mass and diameter and what will be its effect on light?
2
votes
3answers
92 views

What is the binding energy of a black hole?

As the particles which constitute a black hole collapse they become tightly bound. I assume this means a lot of energy would be required to liberate a particle from that bound state. Is it a finite ...
-1
votes
0answers
33 views

Is this derivation for black hole entropy being negative correct?

This "derivation" will use relativity-corrected Planck units to show black hole entropy should be negative. Do you see an error in this line of reasoning? From Einstein's "Relativity" appendix 2 ...
-1
votes
0answers
27 views

Density and behaviour of gravity [duplicate]

If a matter condensed into small enough (schwarzchild radius) we can create Blackholes. I have trouble understanding this concept. Does the black hole created for example by compressing a tennis ball ...
8
votes
2answers
2k views

Why we don't see time dilation in stars orbiting black hole?

We have images of stars orbiting black holes or black holes destroying near stars, but why do we see the stars moving normally? I mean, if time dilation does exist, shouldn't we see that stars slow ...
0
votes
0answers
35 views

Does the effect of spaghettification mean that (speculative) traversable wormholes can only exist from supermassive black holes? [closed]

Assumption that wormholes really exist. Even if humanity could produce wormholes from quantum black holes. These would be never traversable due to the effect of spaghettification? Or does the exotic ...
22
votes
4answers
3k views

Why do physicists trust black hole physics?

Based on popular accounts of modern physics and black holes (articles, video lectures), I have come to understand the following: Black holes are predicted by General Relativity, a classical theory ...
0
votes
2answers
55 views

Do the stellar remnant in a black hole have spatial extent? [duplicate]

I am not talking about event horizons. I am talking about the actual remnant of stellar collapse. Is it just a point, hence the problem with the singularity? Or does it have a finite volume that we ...
0
votes
1answer
44 views

Black Holes' size and emitting [closed]

From the physical observation by space detectors: Do black holes grow in size? Do black holes emit any kind of energy or radiation or something like that?
6
votes
2answers
123 views

Are black holes eternal?

The question might sound very easy - Hawking radiation, however I was pondering that as you get closer and closer to a black hole, time dilates exponentially where the surface of the black hole is ...
5
votes
3answers
103 views

Is the event horizon of black holes visibly sharp, or blurry?

As you come in closer to a black hole, how do you see the event horizon? Is it always like a clear-cut surface? Or it only looks clear-cut from a distance, but as you come closer to the black hole, ...
0
votes
2answers
53 views

Theoretical relativity of black hole and antimatter [closed]

(Theoretically), can black holes be considered antimatter that just cancels its equivalent mass and goes back to neutral stage? Note: Be kind I am not a physicist .
2
votes
4answers
163 views

How can an infinitesimally small object rotate?

How is it possible for an object like a black hole or electron to spin since they are made up of no other components? If my understanding is correct, an electron is an elementary particle which means ...
3
votes
2answers
768 views

How can we detect a black hole accurately?

I know there are many ways in detecting a black hole, but there are odds against them too. So I wanted to know a accurate method to detect a black hole. Here are the known methods to me and the odds ...
0
votes
0answers
30 views

Can we see the photon sphere from outside? [duplicate]

This question came to my mind when i saw the movie interstellar. In the movie there is a scene with a black hole and a sphere of light around it, what i assume to be the photon sphere. You can see it ...
0
votes
0answers
21 views

Do all stars Turn into Black Holes? [duplicate]

If all stars turn into black Holes one day, in far future, what will happen to Earth if Sun becomes a Black Hole.
3
votes
3answers
342 views

Definition of event horizon - Gravity around blackholes [closed]

Put simpler: A black hole is surrounded by a 'sphere' where, to an outside observer. the speed of light is (near) zero. What is the radius of that 'sphere' (for a non-rotating black hole) and how ...
1
vote
2answers
62 views

Possible paradox with black holes and time dilation [duplicate]

I am by no means an expert in the realm of physics. I do from time to time, try to understand the concepts of modern physics and their applications. I came across this video that I am currently ...
0
votes
2answers
54 views

How does a Black hole attract light? [duplicate]

Please no hate for lack of knowledge: I am somewhat fascinated with the subject of black holes. However, I do not understand a concept which is constantly attributed with black holes: that a black ...
3
votes
1answer
106 views

How long can a particle survive inside of the horizon of a black hole?

By examining the causal structure of a Schwarzschild black hole, one can see that a particle in region II is unable to escape to $r=\infty$. Such diagrams do not show, however, how long a particle ...
17
votes
0answers
226 views

How does one correctly interpret the behavior of the heat capacity of a charged black hole?

Consider the Reissner-Nordström metric $$ds^2=-f(r)dt^2+f^{-1}(r)dr^2-r^2d\Omega^2\hspace{2cm} f(r)=1-\frac{2M}{r}+\frac{M^2q^2}{r^2}$$ where I defined the charge-to-mass ratio $q:=Q/M$, which ...
0
votes
0answers
27 views

global transformations in 3d gravity

I am currently working on proper and improper gauge transformations in 3d gravity and btz black holes. (because I have seen it defined with many different ways I will just say that with "proper"and ...
2
votes
0answers
37 views

Are temperature and chemical potential of a black hole independent quantities?

I am a bit confused about the independent parameters in a charged black hole in AdS spaces. From equation (63) of this lecture notes we see that the temperature (T) of the black hole has chemical ...
0
votes
2answers
53 views

Black Hole Growth

When a black hole increases in size by engulfing matter, does this matter fall into the event horizon or does it just rotate around the accretion disk? EDIT: Clarified the beginning of the question. ...
0
votes
2answers
79 views

Do black holes violate the Uncertainty Principle?

If black holes have mass but no size, does that imply zero uncertainty in position? If so, what does that imply for uncertainty in momentum?
0
votes
0answers
32 views

Connection between Black Hole Firewalls and Hawking Radiation

In a previous post, I asked what constitutes a black hole firewall--namely, what is a possible mathematical description of the firewall. Now I have a new question, which is based around this guest ...
1
vote
3answers
49 views

Problem with black holes?

I understand that black holes are formed when supermassive stars (>10 times the size of our Sun) die. When they die, their cores continue to shrink. I have read that eventually the core reaches a ...
4
votes
1answer
254 views

What constitutes a blackhole firewall?

I understand that, to break the entanglement of two particles of Hawking radiation and therefore preserve monogamy of entanglement, there should be a firewall around the event horizon. This firewall ...
8
votes
2answers
1k views

Why don't electrons collaspe into black holes? [duplicate]

An electron has a mass of $9.10938291(40) \times 10^{−31} kg$. It also has a volume of $0 m^3$. This would imply it has infinite density. Shouldn't that make it collapse into a black hole? Why doesn't ...
1
vote
1answer
71 views

Can we observe a star collapse into a black hole? [duplicate]

Let's say that I happen by a star that has just burned out and is collasping into a black hole. I seat at infinity to watch it as a Schwarzschild observer. Will I ever see the black hole collapse into ...
3
votes
3answers
170 views

Size of black hole so large that I could pass event horizon without dying from tidal forces?

Were I to fall towards a typical black hole, the tidal forces would rip me apart well before I got to the event horizon. However, if a black hole were big enough, I could enter the event horizon ...
0
votes
1answer
50 views

Free-fall path into a black hole in Kruskal Coordinates

If an object at t=0 begins to free-fall into a black hole from X in Kruskal coordinates (https://en.wikipedia.org/wiki/Kruskal%E2%80%93Szekeres_coordinates), what does its path on the Kruskal-Szekeres ...
0
votes
1answer
42 views

Would infinite material cause a black hole?

If you have an infinite amount of any material(That doesn't have a critical mass to have nuclear reactions), would this matter form massive black holes that condense into an infinite black hole? Two ...
2
votes
0answers
52 views

Rigorous Proof of General Relativity's Non-renormalizability?

The answer to this question and the comments on it implies that general relativity has not been rigorously shown to be non-renormalizable for all loop diagrams -- only shown for two loops. However, ...
0
votes
0answers
20 views

How is the first law of black hole thermodynamics formulated for a non-vacuum solution with event horizon?

How is the first law of black hole thermodynamics formulated for a non-vacuum solution with event horizon?
2
votes
1answer
92 views

Black Hole surface area at Schwarzschild radius is half?

I have been interested in black holes for some time, and am still trying to wrap my head around some of their more obscure properties. Now I know that the Schwarzschild radius is $r= ...
0
votes
1answer
129 views

Any interesting implications of a holographic black hole in a holographic universe?

Bear with me; I don't have a background in physics, nor am I sure I even understand the things I'm talking about. I recently read that math/physics for a holographic black hole could be applied to ...
-2
votes
0answers
45 views

Point of no return when falling into evaporating black hole

Captain Foolhardy in his trusty spaceship The Test Particle is in radial free fall towards an evaporating uncharged black hole with no spin in an otherwise empty universe which asymptotes to ...
2
votes
0answers
35 views

Help me calculate the Euclidean action of a gravitating system!

I recently read Gibbons and Hawking's paper Action integrals and partition functions in quantum gravity, Phys. Rev. D 15 (1977) 2752. I am interested in repeating their calculations. It is fairly ...
0
votes
1answer
50 views

If a super massive black hole captures a very small black hole, would the smaller black hole be immune to spaghettification?

I think to answer this question we would have to fully understand the nature of black holes. It seems to me that the smaller black hole could have a lower density than the larger one. In this case the ...
0
votes
0answers
42 views

Does the uncertainty principle affect event horizons? [duplicate]

I was thinking about black holes. For a simple black hole the event horizon is given by a distance of 2 times mass (energy) of the black hole. (2m). But according to quantum mechanics, if you try to ...
0
votes
1answer
56 views

Wave equation on Schwarzschild background

I am trying to follow the solution of the wave equation for a scalar field on Schwarzschild background from http://batteringram.org/science/gr/scalar_wave.pdf. I have a problem on page 2 where they ...
0
votes
0answers
33 views

How can a singularity have infinite density? [duplicate]

I've heard many times that black holes have infinite density at their center, but I've also heard astronomers quote mass estimates for black holes. How could the singularity have infinite density if ...
0
votes
3answers
83 views

Path of light as it travels between two black holes

What would happen to light passing through a narrow space between the event horizons of two equal-mass black holes? Would it deviate or follow a straight path?
1
vote
0answers
71 views

Can tachyons escape the gravitational pull of a 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 ...