What is Event horizon: Definition and 299 Discussions
In astrophysics, an event horizon is a boundary beyond which events cannot affect an observer. The term was coined by Wolfgang Rindler.In 1784, John Michell proposed that in the vicinity of compact massive objects, gravity can be strong enough that even light cannot escape. At that time, the Newtonian theory of gravitation and the so-called corpuscular theory of light were dominant. In these theories, if the escape velocity of an object exceeds the speed of light, then light originating inside or from it can escape temporarily but will return. In 1958, David Finkelstein used General Relativity to introduce a stricter definition of a local black hole event horizon as a boundary beyond which events of any kind cannot affect an outside observer. This led to information and firewall paradoxes, which encouraged the re-examination of the concept of local event horizons and the notion of black holes. Several theories were subsequently developed, some with, and some without, event horizons. Stephen Hawking, who was one of the leading developers of theories to describe black holes, suggested that an apparent horizon should be used instead of an event horizon, saying "gravitational collapse produces apparent horizons but no event horizons". He eventually concluded that "the absence of event horizons means that there are no black holes – in the sense of regimes from which light can't escape to infinity."Any object that approaches the horizon from the observer's side appears to slow down and never quite crosses the horizon. Due to gravitational redshift, its image reddens over time as the object moves away from the observer.In an expanding universe the speed of expansion reaches and even exceeds the speed of light, which prevents signals from travelling to some regions. A cosmic event horizon is a real event horizon because it affects all kinds of signals, including gravitational waves which travel at the speed of light.
More specific types of horizon include the related but distinct absolute and apparent horizons found around a black hole. Other distinct types include the Cauchy and Killing horizons; the photon spheres and ergospheres of the Kerr solution; particle and cosmological horizons relevant to cosmology; and isolated and dynamical horizons important in current black hole research.
blechman's statement:
Gravitons are emitted FROM THE SURFACE of the event horizon (remember: gravitons are massless, and therefore move at the speed of light). THAT's what we see. There is NO information (gravitational or otherwise) that can escape from INSIDE the black hole. This is not a...
This question may have been asked before becuase it seems like one of the first questions that would be asked after learning of black holes. My question is, how do gravitons escape the event horizon? They must somehow escape, otherwise the black hole could not influence anything with its...
In another thread it was said:
(my bold)
In Rindler coordinates a "Rindler horizon" forms at a fixed distance below the Rindler observer (accelerating uniformly "vertically upwards" and Born-rigidly in flat spacetime, in the absence of gravity). This horizon has many of the properties of a...
Is there a theory about the relationship, a ratio perhaps, for a Black Hole's event horizon dia. and its actual internal mass dia.? It would seem that there must be a physical mass in there somewhere, of some particular size for a given mass. This ratio may vary proportional to the mass of the...
Consider a particle that has fallen inside the event horizon of a black hole. You can show that
it must have a minimum radial velocity that scales as \frac{1}{\sqrt{r}} for small r. Where, by radial velocity I mean \frac{dr}{d \tau} and tau is the proper time. Doesn't this mean that as...
I posted a similar question under cosmology but the question was unable to be answered. I thought I would try a reframe the question.
When approaching a black holes event horizon, the exit cone for light become smaller until it is eliminated at the event horizon itself. But how can gravity...
A question that's been bugging me:
Why doesn't the gravitational influence of a black hole end abruptly at the event horizon?
Supposedly nothing can escape a black hole, so how does gravity itself escape?
Light cannot escape a black hole, and gravity travels at the speed of light...
Suppose this happens:
10 billion people are taken to a large black hole.
The people are thrown into the black hole as we fly around it in the large spaceship.
I have read that when an object goes past the event horizon, we as observers away from the black hole will see the people freeze...
My understanding is that, according to the Equivalence Principle, accelerated motion is indistinguishable from that of being in a gravitational field. So then, at the Event Horizon of a black hole, where gravity is too great for light to escape, wouldn't that be equivalent to accelerated motion...
I am struggling with an understanding on what the longest proper time an observer can spend before he will be destroyed into the singularity. How should I approach this problem?
My question is: Photons that orbit at the event horizon, require relativistic time to circumvent the circumference of the black hole relative to an observer external to the black hole, keeping Mr. Einsteins second postulate in mind, that being the velocity of light is constant through vacuum (...
I am not clear on how |g_{rr}| \neq 1 in the Schwarzschild solution manifests itself. If I approach the event horizon of a black hole while holding a meter stick "vertically", that is, with d\theta =0 and d\phi =0 between its endpoints, will it appear to someone far away (r \gg r_{s}) that its...
(the story so far … I maintain that, inside an event horizon, there is a useful distinction between "space" and "space-like" dimensions, and that in any realistic coordinate system, time is space-like. JesseM maintains that, in any realistic coordinate system, time must be time-like.
JesseM...
Researchers at St. Andrews University, Scotland, claim to have found a way to simulate an event horizon of a black hole - not through a new cosmic observation technique, and not by a high powered supercomputer… but in the laboratory. Using lasers, a length of optical fiber and depending on some...
Homework Statement
The following statements may or may not accurately describe what you would find just outside the event horizon of an extremely massive black hole like Gargantua (fake black hole), at a distance corresponding to an orbital circumference of 1.0001 times the horizon...
http://upload.wikimedia.org/wikipedia/commons/1/1d/Event-horizon-particle.svg
Would there still be a t axis? Would the yellow cone get squished (become one-dimensional) and stretched over the x axis?
Or would it stretch to infinity along the t axis and spread over the entire (x,t) plane?
Okay, let's say I'm orbiting a black hole right near the event horizon. If I take a long stick and poke the black hole what happens? If time stops for the end of my stick as it reaches the event horizon how can I keep pushing on my end? For that matter if I jump in feet first doesn't my head see...
Hello,
I's a spead though that black holes swallow everything in it's vicinity.
But, something bothers me : when we close on the event horizon of a black hole from the outside, the gravitational field tends to be infinite, and at the surface of the horizon it is infinte. So to say, that...
To Physicists/Administrators/Moderators:
The following two facts raises a doubt
1) "No influence can travel from inside the Event horizon of a black
hole to the outside of it AT or below the speed of LIGHT (V<=C)."
2) "Gravitational influence travels AT (or below?) the speed of light...
As the tile says, anyone's got an idea what the g-forces might be at the boundary of a black hole's event horizon? I got a formula to calculate the event horizon radius but not the the gravitational forces. Equivalence to Earth G's would be nice or in m/s2 = meter per second squared!
Is it...
this is a case where it could be very helpful if someone (Pervect? Wallace? hellfire?) who has the numbers handy could tell us how far away the CEH is at present according to the usual LCDM model
I don't know the exact figure. I think it is somewhere around 16 Gly.
that is, slightly further...
Dirac's Sea is described as an infinite sea of filled negative energy states. Dirac produced this idea following his formation of the original Dirac Equation, which required the inclusion of negative and positive energy.
From the Event Horizon of a black hole spacetime is so warped that...
I'm told that the cosmological event horizon produces a temperature at every point of space similar to how a black hole event horizon produces a radiation near its surface. If there exists a temperature, then there must be particles to produce that temperature. They must be baryons since normal...
My questions are these: When a Black Hole is detected, Is it found by its Event Horizon? Is the Event Horizon located in relation to the stars equitorial plane? If I were to approach a Black Hole from its "North Pole" or "South Pole", would I be affected by its Event Horizon?
Has anyone got a reference to the entropy of the cosmological event horizon? Is this entropy an upper limit of the entropy inside (like a black hole) or a lower limit?
I'm entertaining the idea that a shrinking cosmological event horizon puts a shrinking upper bound on the entropy inside it...
I got to thinking the other day while watching Superman Returns about the scene during the opening credits where it shows the accretion disk around a black hole. The scene showed an inward spiral of gas and other matter increasing speed as the matter approached the event horizon. Now...
The newly release WMAP data supports the Inflation model that the universe expanded from subatomic scales to Astronomic scales in a fraction of a second. If so, then what would have been the distance from each point where space would have been expanding at the speed of light, approximately? Thanks.
i haven't yet got this concept. i have read about the time "freezing" near a BH , but am not clear. can u please explain what actually happens? why does the time stop? i also want to know one thing-- when, supposing 'A' enters the event horizon he moves slowly towards the singularity because of...
hi,
i was just wondering as the mass of the black hole keeps increasing due to increased mass getting deposited on it does its event horizon increase
because of this?
does the black hole have infinite density?
-Benzun
Hi All,
I am new here, Iam interested in Cosmology, sometimes I find many questions which I don't find its answers directly in textbooks or I read it but couldn't understand it, for example I have a confusion between horizon, particle horizon and event horizon, would you please help me in...
For an object exactly at the event horizon of a black hole, is the acceleration infinite or does the object accelerate at the speed of light?
I have read that the force on the object causing it to accelerate when it is at the event horizon is infitite (so the acceleration would be too), but the...
light in the event horizon does not come out, right. If this is due to gravity will light on the edge of the event horizon, butnot in it, be bent, so that when we look at the light beside a black hole, it is not coming from the behind the black hole, but from an angel.
___________s...
Hey, my first post here, glad I've found somewhere on the internet to discus this crazy stuff!
Anyway here's my question:
Matter falling into a black hole accelerates towards it under its gravity, towards the "event horizon" (or Rs=2GM/c^2)
The relativistic version of the law of...
I do a little project about photon at the event horizon. I use GR to proved that anything in the event horizon can't escape from black hole, but a Prof. say that I must use string theory.But I did't accept with him.So, if someone know about it.Please Help me :cry: .
(I have to tell you that...
Consider a Schwarzschild spacetime. If the singularity due to the point mass is removed (e.g. with an homogeneous matter distribution), does the event horizon disappear? If yes (I assume this is the case), how can be proven that there exists no event horizon if there is no singularity? May be it...
Ok, let's say we wanted to know the diameter of the largest black hole. (Its event horizon) Let's say the universe had contracted and all the galaxies had been consumed by black holes and all merged into one single massive hole.
Say there were approximately 100 billion galaxies, all...
Escape velocity at particular radius from the gravitational source means the initial speed that an object needs at that raduis in order to coast without limit ("to infinity") without ever falling back to the gravitational source. If the escape velocity at a radius is so large that nothing...
Many websites claim that someone falling into a black hole would be ripped apart by tidal forces as he crosses the event horizon. Others say that the falling observer feels nothing special as he crosses the event horizon - he doesn't get torn apart by tidal forces until he gets close to the...
Is the event horizon of a black hole (as seen by an observer at rest relative to the singularity) equivalent to the singularity (as seen by a free-falling observer)? In other words, if the stationary observer watches a rocketship free-fall to near the event horizon then turn on its rockets and...
Was wondering: In Hawkins's " Univers in a nutshell" book, he talks about the behavior ov virtual particle pairs around the event horizon of a black hole. My understanding is that one of the antiparticle of the pair can be absorbed by the black hole. This makes for the release of the particle (...
Was wondering: In Hawkins's " Univers in a nutshell" book, he talks about the behavior ov virtual particule pairs around the event horizon of a black hole. My understanding is that one of the antiparticule of the pair can be absorbed by the black hole. This makes for the release of the...
One of my friend had asked me one question which I did not really have a good answer for. His question was: Why does the antiparticle counterpart of the virtual antiparticle pairs (those that appear due to uncertainty between time and energy) at the event horizon fall into the black hole...
[SOLVED] Two black holes and the event horizon..
What happens if a black hole enters another black hole's event horizon??
I really wonder can matter escape by the gravitational chaos??
I asked this question to the scientist in NASA haven't received the answer yet..But this is a...
All right, physicists claim that mass can be at infinite density. This condition is called the singularity, an one-dimensional point that is having mass (or energy, whatever)inside it.
I say mass cannot possibly form singularities. Why? Because of the following:
When there is mass inside...
The spacetime geometry outside a black hole may be transformable through the event horizon as the black hole internal geometry, and conversely.
Consider Hawking radiation with respect to black hole entropy. While one quantum escapes to universal infinity, the other approaches the...