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.
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...
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...
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...
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.
Black hole drive in the film "Event Horizon"
Cheesy movie, right? A lot of fun though. For those who don't know, there is a starship in the film called the Event Horizon, which utilizes an artificial black hole drive/engine in order to allow it to fold space, although it's probably more...
I recently saw a video where it was stated that black holes may have an inner 2nd event horizon where beyond it is trapped light and energy! I have searched the web for an explanation pertinent to this hypothesis but found nothing.
Can anyone shed some light (if possible)?
Cosmo calculators and tabulators a primarily about the PAST expansion history and they give learners hands-on understanding by being able to vary the model parameters and see change. That's good. I sometimes notice a difference here at PF between how posters with mainly verbal understanding...
Varying coordinate systems in GR has given me a new perspective that may help to resolve a problem that has been nagging at me ever since I began working with GR. In every problem I've ever dealt with, a complex mathematical result describes an impossible scenario, something that cannot occur...
Is there an event horizon beyond the visible universe where the laws of physics kind of get cut off, a limitation to the reach of gravity.
I ask this because if space is expanding there must be a point that if light left Earth it could never come back because the return distance is expanding...
hi, I am not a physicist so sorry if this is a stupid question, its just curiosity.
how thick is the light like event horizon of a schwarzschild black hole,
for instance, what the closest distance scale that an infalling photon and an escaping photon be, and whatI is "inbetween"? I've heard...
In the book "The Black Hole War" by Leonard Susskind, he states that a person can live past the event horizon (to a certain point, of course) in a massive black hole because "the horizon of the larger black hole would be so large that it would almost appear flat. Near the horizon, the...
I'm curious - once an object passes the event horizon the image of that object remains on the event horizon only to become more redshifted rather than dissipating. two questions: 1) why does the image remain if the light stops traveling? if the light cannot travel to the observer, than there...
Hey guys this is my first post so I hope this doesn't come out stupid since I only know slightly more than a layman. Recently I have been trying to wrap my mind around what happens inside an event horizon. Specifally I have been confused with the matter which resided inside the schwarzchild...