Event horizon Definition and 308 Threads

The event horizon is a null surface in spacetime separating events that are causally connected to an observer from those that are not. Does anyone have a good, simple argument on why it must be a null surface?

My question is: Is my picture of what happens as something approaches an event horizon accurate - and are there any citations describing it? I got my "picture" from a PBS broadcast several years ago. It was since mentioned in these forums, but I haven't been able to find an explicit mention...

As all of us know that in a vacuum the particle antiparticle pairs or the virtual particles are created violating the law of conservation of energy. So even near an Event Horizon of a Black Hole virtual particles are formed. One of the particles gets sucked into the black hole but the other...

If one of two entangled particles passes the event horizon of a black hole, will the entanglement still exist? Because that would mean information can come from a black hole.

A number of recent threads have discussed what happens when an observer falling into a massive black hole passes the event horizon. What I would like to know is this. For a massive BH of mass M, Schwartzchild Radius Rs, how long would it take for such an observer (who, presumably crosses the...

Does anybody understand the fundamentals of what is happening in this circuit? Tungsten welding info is all about high current... but this is a low current scenario. AC input, CDI Coil generated 20Kv (estimated) suffers voltage drop over 100mm of tungsten rod. The larger the diameter... the...

I recently read a few articles that contradict Einstein's Singularity theorem. The idea being that black holes are wormholes to other universes; with a white hole on the other side of the black hole (Poplawski's theory). What if instead of being a portal to another universe, the Event Horizon of...

Dear all, In one of his lectures,Prof. Susskind mentioned that the event horizon "bulges" forward to meet any incoming radiation or matter; and it is a property of Einstein field equations. I have not come across any such property, and if it exists, shouldn't it belong to the Schwarzschild(or...

I'm trying to understand the ideas in this paper at a nontechnical level: Laura Mersini-Houghton, "Backreaction of Hawking Radiation on a Gravitationally Collapsing Star I: Black Holes?," http://arxiv.org/abs/1406.1525 She says: This work investigates the backreaction of Hawking radiation on...

The event horizon, or schwarzschild radius for a black hole with the mass of the Earth is 3 km. But according to http://hubblesite.org/reference_desk/faq/all.php.cat=exotic, objects would have to be as close as about 6.2 miles (10 km) to the black hole's center before they began spiraling in...

I am currently reading "Our Mathematical Universe" by Max Tegmark. From the book I learned a couple of things I find startling: 1. The event horizon, beyond which galaxies run away from us faster than light and hence cannot be seen by us, is about 14 billion light years away. 2. Our...

say you fell beyond the event horizon of a black hole can another black hole passing close enough pull you out?

I'm looking for proof that Wolfgang Rindler coined the term Event Horizon. I believe that it was Rindler because that's what I've heard from reliable sources, e.g. http://www.mathpages.com/home/kmath339/kmath339.htm Thank you in advance.

Theoretical question... If an extremely long object approached the event horizon, let’s say a torpedo shaped craft 1 mile long. The craft would get stretched and the observer’s time would become dilated as the craft/object approached the event horizon correct? Would it ever be possible for an...

In "The Hidden Reality", Brian Greene mentions almost off-hand that inside the event horizon of a black hole, space and time are reversed. But no details are given. What, precisely, does this mean? Does it mean that in one's equations, if one is using a (-,-,-,+) signature, then everything...

Although the subject line might seem to put this question inside general relativity, the reason I put it in quantum physics is because I would like to know what happens when one treats a singularity as a particle. Obviously from outside the event horizon, one cannot do this, but inside the event...

Lets say we have a couple objects, one very close to a black hole, one a little farther out and then one a good distance away. Would the one very close to the black hole see the other ones time moving much quicker than their own time? How about just as they are going to hit the event horizon...

I have a doubt/question/idea what ever it may be some thing like this Theoretically is it possible if we place one of twin electrons(Quantum entanglement)into event horizon of Black hole and observe the second one on earth, so that what is happening in Black holes? i.e how electron's inside...

I have always assumed once we pass through a black hole's event horizon, we can throw away the return ticket. But I have been thinking - is it really so final? Consider two identical black holes close to each other with their even horizons overlapping, or nearly so. Is the spacetime on a...

Here's the question: One of the brightest stars in our night sky is a red supergiant with a mass about 10× the Sun’s mass and a radius about 1000× the Sun’s radius. At the end of its life it will explode as a supernova and then collapse and become a black hole. How large will the black...

Why does time stop in the event horizon of a black hole? Or at least slow down, from what i know.

Lets say I fall into a super-massive black hole's event horizon. Facing outwards towards the event horizon (with the singularity directly at my back), turn on my flashlight. Will those photons emitted by my flashlight actually be able get any further away from the singularity than I was...

Hi, I read a while back that astronomers were able to view an old supernova explosion using a technique that involved looking for light reflected off some hydrogen gas. After thinking about this for a while, I decided to come here with my question. Is it possible to use this technique to view...

When I look at a minkowski diagram for a black hole I can see that time goes to infinity for the outside observer while the infalling object approaches the black hole. That means that for an outside observer, it takes an infinite amount of time until the infalling object reaches the event...

What are the odds that there is a different event horizon for dark matter?

Hello, I am trying to draw an analogy, which just came with a flash in my mind. Please clarify me, if it is wrong. Kindly note that it is an analogy only. An event horizon -- Where the light emitting is not strong enough to go inside the black hole also it cannot go outside the zone and...

If you click on Jorries calculator http://www.einsteins-theory-of-relativity-4engineers.com/LightCone7/LightCone.html you see in the default table that immediately comes up (without your doing anything) that the present-day CEH is 16.5 billion ly. What does that mean to you? How do you picture...

Homework Statement I got a problem wrong on a quiz and I'm pretty positive on all the other questions as being correct but maybe this one.. How does the gravitational force at the event horizon (Schwarzschild radius) behave as the black hole mass increases? Homework Equations...

I just registered and am not entirely sure this is the right section of the forum to ask, but regardless... My understanding of gravity is that it is a wavelike distortion in spacetime which travels not instantaneously but at the speed of light, and may also be describable in terms of a stream...

From a distant frame of reference a falling object never reaches the event horizon due to time dilation. If I drop a meter stick into a black hole lengthwise I should see both ends of the stick getting asymptotically closer and closer but never reaching the horizon, thus the stick should appear...

Hi, I'm new and uneducated. Would like to know how to reconcile space-time being considered asymptotically flat near the event horizon and beyond, with the observable fact that stars do indeed orbit the black hole. I understand those orbits are not near the horizon, and I believe all the...

Basic question I'm sure, but here goes; If the following is correct; An object may be considered to be 'at rest' when there are no inertial forces acting upon it (ie; it is not accelerating). A satellite is at rest because it is in freefall. A person standing still on the Earth's...

From previous threads I have understood that crossing the event horizon of a supermassive black hole is nothing very unusual for the falling observer locally. Usually in these considerations the falling observer has been thought as a "point" without much dimension. How about if Earth (and...

Wikipedia says, "Likewise, any object approaching the horizon from the observer's side appears to slow down and never quite pass through the horizon, with its image becoming more and more redshifted as time elapses." So does this mean from the outside observer's perspective, that nothing ever...

Im sure there must be something I'm missing here. Can someone please explain to me? You're outside a black hole event horizon and you have two identical objects. If one object were released from only 1 meter above the event horizon, and another were released from a million km away...

You may be weary of the repeated questions about event horizons. The concepts are slippery. Imagine Bob and Alice. Bob free falls into the black hole. For simplicity, assume he falls along a radial geodesic with no tangential component. Alice remains outside to observe. Alice observes...

I've been told that time slows down so much inside a black hole that an event horizon never actually comes into existence and that we don't know what happens inside a black hole. Is it true that the event horizon never comes into existence - or at least, if time slows down like general...

This is a question someone asked me today and it's bugging me allot. If the acceleration caused by gravity is greater than the speed of light at a black hole event horizon then does this mean that the matter is falling at faster than light speed?

PLEASE LOOK ATTACHMENT! Star mass affects event horizons diameter.But we know that Black hole's foundation is singularity so we can understand that singularity affects event horizon diameter. Example:Imagine there are two stars, first star mass is 5 star mass second one is 7 star mass...

The universe is expanding as described by Hubble's law, which means that at a certain distance from an observer, expansion exceeds the speed of light, so all waves become infinitely red-shifted. In other words, if an goes beyond this point, no information about it can ever come back to the...

From a GR perspective, how does the event horizon of a black hole know how to behave? Consider a simple scenario of a shell of material outside the event horizon of a black hole, in free fall. Once the material is consumed by the black hole, the event horizon will be greater, but my...

In another thread, which I don't want to derail, the issue came up as to whether or not the event horizon of a black hole is physical. Some contend that it is physical but I contend that it is merely a set of coordinates (most easily represented by the spherical coordinate R). I DO...

I am just an amateur, so go easy on me. I am simply confused about schwarzschild radii and relativity. It seems to me that if you had two observers, one far away from a black hole, and the other just outside the event horizon, and you allow any small amount of time to pass, they would...

Hi everyone, and happy new year if you happen to be reading this tomorrow. Rather than partying, I am writing up 100+ pages of astrophysics lecture notes, which I think will take infinite time as I keep getting stuck on every other line. My current problem is with the equation for the...

What's the difference between apparent horizon and event horizon? I checked Wikipedia but I still don't understand. Could anyone give a short explanation? Thanks!

Hi everyone, I have read a few different ways of looking at this problem, and it's one of those things where I am happywith the answer, just not how to get there using proper mathematics. My lecturer described this with some complex integrals involving E (but I'm not sure what that is!) but I...

I am under the impression that the event horizon radius of a non-rotating black hole is equal to its Schwarzschild radius. Is this correct? If yes, then I have a mixed bag of questions: Is the event horizon radius always calculated using the Schwarzschild metric, no matter what model we are...

The event horizon of a Kerr black hole is often depicted as being spherical, but this seems to be a reference to the horizon as defined in Boyer-Lindquist coordinates, where horizons appear at a constant value of r. However, Thorne describes the "black hole's horizon bulg[ing] out at its...

If I flew over to a the nearest black hole with the Hubble scope on a trailer (cough), how would the performance of the scope differ from current, particularly with regards to observing extremely distant objects. In particular, when time dilation becomes extreme as my orbit of the BH nears...

The event horizon Wouldn't it be possible for light to orbit a black hole inside the event horizon? In other words, the event horizon, while being a point of no return, is not necessarily a point of ultimate doom.