Event horizon Definition and 307 Threads

Reading "Exploring Black Holes" I find that a particle following a geodesic towards a black hole always reaches the speed of light c when crossing the "event horizon" regardless of the reduced circumference that the particle begins at (1mm or 10 million light years). This would also...

I saw this question posted in a Yahoo forum. I would be interested in the answers from the people here: "We can all agree that the more massive a black hole is the smaller the circumference of the black hole's event horizon will be. Therefore, can a black hole ever have enough mass to where...

If this is in the wrong section, my apologies, but I'm wondering if it's possible, with known equations, to calculate the final velocity of matter accelerating into the event horizon of a black hole, and what those equations would be. I don't think this is an easy question, so any help is...

As I understand it, an Event Horizon is a boundary surrounding a black hole where light is held 'still'. If the photons never get beyond this boundary, how can they be observed?

Black holes, Time technically stops after the event horizon correct? So, Let's say, We had a string.. That cannot be ripped, broken, streched, or anything that would harm or alter it's position. Let's say, It was 20,000 Light years long and on each end of it was a black hole pulling. Now, We'd...

I would be grateful if someone could point me to a description of how a sphere of freely infalling matter ---- say equivalent to that of a collapsing massive star --- generates an finite-sized event horizon, as observed far from the incipient black hole. I can only imagine that the event...

Some thought experiments and questions. I would much appreciate any comments on whether my analyses below are correct. 1. I am falling feet first into a black hole. An external observer will never see me fall past the event horizon. However, in my frame of reference I will fall past it in...

Given present theory, how would a laser photon stream behave at a tangent point to an event horizon (EH)? Is it possible for a photon stream to orbit a black hole? Could the beam be split at the EH with one branch spiraling into the black hole while one branch follows some geodesic (perhaps not...

'Poking' the Event Horizon Forgive what is probably a ridiculous scenario, I was having a discussion earlier :smile: We have Black Hole A and Black Hole B of completely (or near) equal gravitational field strength. http://img148.imageshack.us/my.php?image=blackhole1.gif A...

According to an outside observer, an object slows down as it approaches the event horizon but never reaches it. Why does it slow down? Thanks.

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...

I wonder about something. How big would the event horizon of the universe be when all matter was infinitely packed together?

[SIZE="1"](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...

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...

As a massive star begins it's collapse into a singularity, at what stage does the event horizon form?

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...

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.

What is the difference between particle horizon and cosmological event horizon?

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...

Could someone give me a formula that would describe an event horizon, and also explain your view?

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...