Black hole Definition and 999 Threads

Hi all, I was wondering if, when a beam of light is pulled towards a black hole , because it can't accelerate, it is blueshifted? Thanks in advance.

A galaxy is many many light years away. All Electric Charge, Q, must be dissipated. How do you tell if charge exists and what magnitude.

If a beam of light is on a trajectory that is perfectly tangent to the event horizon of a black hole (or a little below tangent, allowing it to "dip" into the EH for a moment), is it possible that that photon could be pulled into a never ending orbit around the black hole? Or is the gravity too...

is black hole a theoretical concept or a natural phenomenon?

I was thinking about the supermassive black hole that is theorized to be at the center of our galaxy, and indeed, at the center of most galaxies. If that black hole is continuously consuming the stars, planets and gas around it, given enough time, will it not consume the entire galaxy that...

"Rewinding" a black hole - Can a spinning black hole become a star? I couldn't fit all the important prerequisites and context in the title, so I'll set up the thought experiment here. Some of these assumptions are also questions, and might be easily refuted, thus answering the main question...

I was watching a documentary about the universe and it claimed that black holes were sometimes as small as 2 kilometers across. Now before this, my general understanding of a black whole was that it had no physical extent in space, that it was just a 1 dimensional singularity, and the black...

Given a massive object that has entered a BH's accretion disk, what percentage of its mass is typically re-radiated away as i) accretion disk radiation and ii) polar jet radiation/particle streams before ever getting to the event horizon? How much does a black hole *not* consume of its...

Hello, I would first just like to introduce myself I'm Adrian and I am a grade 11 student so this type of stuff is way out of my league in terms of mathematical complexity.. but are there equations that define a black hole (What is happening to particles when they enter the event horizon.. etc)...

Holographic BB out of prior BH (stringy version of BH bounce) http://arxiv.org/abs/1309.1487 Out of the White Hole: A Holographic Origin for the Big Bang Razieh Pourhasan, Niayesh Afshordi, Robert B. Mann (Submitted on 5 Sep 2013) While most of the singularities of General Relativity are...

The Schwarzschild equation for a black hole's event horizon is rsh = 2GM/c2 or (1.48 x 10-27 m/kg) x M. Thus, the ratio of mass to radius is 6.7 x 1026 kg/m for all black holes. If the mass and radius of the universe are calculated as follows, Mass of the gravitationally connected universe...

Black holes have an entropy, but they evaporate. At the end of the evaporation, the entropy is greater than the entropy at the beginning of the evaporation. I am looking for an example of a quantitative result for the entropy of the black hole after evaporation (or the entropy difference...

I was under the impression that one of the ways of representing a black body (for explaining the ultraviolet catastrophe) is as a 'resonant box'. Frequencies lower than the dimensions of the box cannot be contained within and the black body is thus 'transparent' to those frequencies of light...

As I understand, complementarity approach claims that there are 2 different stories, for an infalling observer and an observer @ infinity, they are different, but no observer can confirm both. But it violates the Block Time/Eternalism, where time is a dimension, the whole world is a static...

Imagine we have a very tall vertical cylinder like a very elongated telegraph pole, that is rotating at 200 rpm about its long axis on near perfect bearings. Initially the cylinder is sufficiently far from a black hole, that differences in gravitational time dilation between the top and bottom...

Author: Leonard Susskind Title: The Black Hole War Amazon Link: https://www.amazon.com/dp/0316016411/?tag=pfamazon01-20 (submitted by jedishrfu)

For outside observer, an object falling into black hole seems to freeze at event horizon and never cross the boundary and proceed inside the black hole. This is of course not the case in the falling objects own reference frame. Depending on the size of the black hole, a falling object may not...

I thought readers would be interested in this interesting article today on black hole and neutron star mergers and the very small possibility of instantaneous sterilization and extinction of all life on earth:http://www.space.com/22231-gamma-ray-bursts-neutron-stars.html...

hi some black holes are inner and outer horizon! what's this means? inner and outer? what happen between them?

consider have a metric ds^2=f(r,t)dt^2+g(r,t)dr^2+k(r,t)dΩ^2 if g(r,t) =0, we have black hole? any metric that has this condition, are black hole? or not this is first clue to determine black hole and we should check some other features! solution of g(r,t)=0, may have some roots, for example...

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...

From here: http://www.reddit.com/r/askscience/comments/f1lgu/what_would_happen_if_the_event_horizons_of_two/ (About a page down from the top. You can't miss it.) Imagine, just for a moment, that you are aboard a spaceship equipped with a magical engine capable of accelerating you to any...

Arkani-Hamed, Dubovsky, Nicolis, Trincherini, and Villadoro argue in section 2.2 of A Measure of de Sitter Entropy and Eternal Inflation that the effective field theory description of black hole evaporation fails after a time t[SIZE="1"]ev, even though the curvatures are small. Almheiri...

Sorry if I am woefully uninformed, but I am really curious. What happens to time at the center of a black hole according to general relativity?

hi if you want to find the black hole solutions, what do you do? has any solutions of $R_\alpha\beta=0$ a black hole? thanks

what is the final stage of black hole mean what its the next stage turning to be (in what form ) why black hole is created?

In a thread some time back on black hole firewalls, one of the papers linked to was one by Bousso in which he argues that (as the paper is titled--note that this is a revised version, the original was quite a bit dfiferent) "Complementarity is Not Enough". I'm not trying to start a general...

What is the central region of the so called black hole composed of? Are there intense energetic waves caused by thermonuclear fissile processes? Does the high intensity ray conflagration coupled with immense crushing cause electron repulsion?Does this process also cause nuclear disintegration...

Ok so this has always confused me and I still can't seem to find an answer anywhere! A general black hole has parameters M, Q, and J which are given the meaning of mass, charge, and angular momentum. My question is what what is the contribution to M by Q and J?? Presumably if you start with a...

So, I was thinking about this the other day. If we watch material approaching near the event horizon of a black hole get scattered all over the place, then would the opposite be seen for an observer falling into a black hole? Instead of us seeing them scattered all over the place, would they see...

Following a Big Bang, if the Universe expanded at the speed of light, then the Laws of Physics would have come into play long before the radius of the Universe passed it's own Schwarzschild radius. Does that mean the Universe cannot keep expanding forever ? or maybe that we exist inside a...

Hello, I am new to this forum! I have only just completed my first physics class, but I like to learn about some of the more advanced topics in physics on my own time. I was watching a video about black holes and I noticed a part of the video that stated "any matter that enters this...

I had a discussion regarding the region of spacetime visible to an observer falling into aSchwarzschild black hole. Using Eddington-Finkelstein coordinates this is rather straightforward, at least graphically. However the situation is rather artificial b/c the BH exists externally. So my...

I think black holes are amazingly interesting and I hope we get some answers about what they are in the future. I have a question I hope someone can help me with. The Schwarzschild radius is the radius at which the gravity becomes so strong there is no going back right? Is there an equation...

I'm reading Einstein's Cosmos by Michio Kaku, and he describes Kerr black holes; which are apparently rings of matter stabilized by centrifugal force. Anyway, Kaku throws out that if you go through the event horizon of a black hole, you will be transported to another universe; he says this as if...

How do we know which one is a black hole solution(metric) or a wormhole solution(metric)? what is its feature?

When a black hole is formed officially from a collapsing star (consider the simplest case of spherically symmetric collapse of non-rotating spherical star)? I see two possible answers: 1) At the moment when the radius of the star crosses the event horizon (##r_{star}=r_s##) , but the...

So I always hear that the density of a black hole is infinite, because it's volume is zero. How can this be if, in mathematics, n/0 ≠ ∞? Would it be more correct to say a black hole's density is undefined or indeterminate? I also hear that some people say that a black hole's volume is...

Even before I had seen a Kaku documentary on black holes creating new universes, perhaps with different physics on the other side of them, I had had this image that the Big Bang was caused by a collapsing point singularity in a parent galaxy. Surely there must be something wrong with this...

I have been fascinated by stars and Black holes for most of my life but one of the things I can't get a satisfactory explanation on is what gives a Black Hole it's mind boggling gravity. We know that a Black Hole cannot be seen because it's gravity is so great that not even light can escape it...

I have a basic question. It is well known that according to "our" time (time measured by an observer in flat space-time), an object falling into a black hole will never cross the event horizon (though, of course, according to its "proper time" it will fall into the singularity in a finite time)...

I am currently working myself into black hole physics and I am interested in their possible quantum geometric description by means of LQG. Can anybody please tell me good sources to start with? Since black holes were studied in this framework for a longer time, what is the most recent...

I want to know what is the shape of a Black Hole? Is it round like a globe, or is it flat or oval shaped?

I hear that black holes evaporate, but does it all get converted into Hawkins radiation? And what role do white holes play in evaporation?

Little thought experiment. Hypothetically let's say I'm standing on the surface of an imaginary black hole and not completely crushed to death, or better yet, I'm in the center of the thing (never mind the singularity) and looking outward into deep space. Is the light coming toward me red or...

If two stars, both slightly above their Schwarzschild radius collide, can a joint horizon form before they come in contact? What if one is matter, and the other the same amount of antimatter? Will they annihilate each other completely to pure radiation, which stays within the horizon? Would...

The solution of Einstein's field equations for a simple black hole show a slowing of time as you get close to the black hole. Time stops at the event horizon. An observer in flat spacetime far from the hole would see an astronaut fall slower and slower as he approaches the event horizon. It...

When the sun is collapsed will it form a black hole?

How can a black hole have a high entropy state if the matter inside it is in a supercondensed form with maximum density,which means less degrees of freedom therefore less entropy than normal matter.Like in neutron stars we have low entropy with the neutron degenerate matter and yet a black hole...

Is there any such thing? Or is it unphysical? If it's physical, would making contact with a matter black hole result in E=mc^2? Thanks.