Black hole Definition and 999 Threads

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.

How can two Black holes fusion and consist a supermassive Black Hole ?!

In a recent lecture by Stephen Hawking he mentions that our universe started as a singularity. Can this singularity be caused by energy from a Black hole in another space and time? This in turn would mean that an infinite number of universes can be and are created.

Hi I just listened to Leonard Süsskind Lecture 7 on youtube about General Relativity in the following link. At 1:28:00 he mentioned, that if a object is very close to the surface of a black hole, then the matter at this point would bulge out until it get completely absorbed. I don't...

Hey, before people start throwing rotten vegetables at me, I'm not any good in general relativity! So my question is: are black holes transparent to electromagnetic waves of wavelengths on the same order as the Schwarzschild radius of the BH?

I assume people much more knowledgeable then me must have already thought this through, but the following line of thought has me very curious. I'm making a lot of intuitive leaps here though, so I am sure there is a lot of places I could have gone drastically wrong. Hawking radiation is...

What blue shift of distant light would you observe, while free falling into a black hole. It seems that hovering at the horizon (which is not possible), would result in infinite blue shift. But what about the observed blue shift in free fall, as a function of the radial Schwarzschild coordinate?

What is the maximum approximate black hole size that would have negative growth rate as a function of average local mass density (and/or any other relevant parameters)? In other words, when does an evaporating black hole become a growing black hole and vice-versa? Cheers Eric

If a small round black hole is traveling normal to the center of the major plane of a larger toroidal black hole, is it possible any energy will "get thru" to the other side of the toroid? . It's said that once you wander into a BH, you can't get out. It's like a tar pit but worse. Maybe...

This scenario is described by Lenard Susskind in a lecture on general relativity starting at time stamp 44:23 in the following video. The scenario is that a spherical shell of radiation is directed inward to a point. The shell contains enough energy to form a black hole. He states that...

i heard when 3 black hole crash one which come latter will pushed away and two wil become one big black hole here, why black hole pushed away?? im korean so i cannot write exactly sorry

Gravity on Earth is 9.8m/s² and on the moon I believe it's 1.6m/s² so I'm wondering how much gravity a black hole has? What is the minimum force of gravity needed to bend space-time, do we know? Is there a formula? Also how far from the black hole would you have to be before you no longer feel...

Now what I'm about to say may sound like a sort of speculation but not in the typical bad way. Now we have a black hole in universe somewhere.(Doesn't matter where for my theoretical purposes) Now we know that once a big star looses all or most it's fusion elements and some of it's mass that...

I watched this documentary about an argument involving information loss in a black hole, Stephen Hawking managed to wind everybody up by claiming information was lost and therefore broke existing laws of physics. Its an old recording so it may not be relevant anymore but one part of this...

Hey I heard from a couple differnt places on the internet that there's a possibility that a black hole hypothetically could be formed by the LHC. I thought that black holes were formed by the implosion of a huge star that keeps going in on itself due to gravity. Is it true that this could happen...

A clump of matter does not need to be extraordinarily dense in order to have an escape velocity greater than the speed of light, as long as its mass is large enough. You can use the formula for the Schwarzschild radius Rs to calculate the volume 4/3piRs^3 inside the event horizon of a black hole...

I found this extremely handy reference on Black hole calculations and models to measure black hole accretion disk/jets. The article also covers several types of BH non rotating and rotating. Methodologies that can be used to distinquish between Neutron and black hole event horizons...

If black holes crush things into infinite density, shouldn't they all be the same size?

If the universe was at or near a singularity in the past, why is it not a black hole now? How can part of the universe become a black hole, and not the whole universe?

This is a simple question, right? Well, no. Many theories have been conjured up and broken down. However, I just want to know what all of you think or theorize about the point past the event horizon of a black hole. Does it lead to a parallel universe? Does it destroy information, a breaking...

This is a puzzle based on a purported "refutation of GR" on http://finbot.wordpress.com/2008/03/05/no-black-holes/, which is also the subject of a subthread in this Hacker News discussion. (Btw, the Hacker News discussion contains my answer to the puzzle if you scroll down enough, so you're on...

A recent thread on Hacker News led me to this paper by Poplawski: http://arxiv.org/abs/0902.1994 The abstract says: "We consider the radial geodesic motion of a massive particle into a black hole in isotropic coordinates, which represents the exterior region of an Einstein-Rosen bridge...

Hello, Does a star collapse directly to form a black hole without creating a supernova or whether a supernova forms some neutron stars which after crossing the TOV limit forms a black hole? Thanks.

Hi! I am not much of astrophysicist or something but read something about Black hole information paradox in a book. Could anybody please explain me what is the meaning of term and why does it happen? P.S. Please include Hawking's radiation as well Thank you in advance

Homework Statement In a previous problem I had to find the entropy of a black hole where I ended with this: S_{BH}=\frac{8 \pi^2 G M^2 k}{h c} Now I am to find the temp, given the energy of a black hole is mc2. Homework Equations T=(\frac{\partial S}{\partial u})^{-1} The...

In this FAQ at the Baez website, the big bang singularity is contrasted with a black and white hole as a possible beginning of our universe. Is the Big Bang a black hole? http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html [I'm not interested in answering the title...

Hi, I recently came across this formula: [SIZE="3"] T = \frac{\hbar c^3}{8 \pi GK_BM} As I understand it deals with the radiation that is believed to be emitted by a black hole. Does it describe the temperature of the radiation? Thanks

When the 'evaporation' of a black hole supposedly occurs, it is always attributed to 'Hawking radiation.' As I understand it, Hawking radiation occurs when a virtual particle pair is 'split' at the exact edge of an event horizon. When this occurs, one of the particle pair escapes to 'normal'...

One speaks of the Big Bang initial condition as a singularity possessing an extremely low entropy (to explain the growth of entropy throughout time to our present stage of the universe). If that singularity truly possesses infinite density, that would make perfect sense, since what would become...

In thermodynamics, I assume that any closed system that can be described in terms of individual objects/particles and their associated individual momenta has both entropy and temperature. A priori a black hole seems to me to fit that description of a closed system. Why was it significant...

I recently asked myself the question "If all the stars in the universe condensed together to form a black hole how big would that black hole be?" Using the information from http://en.wikipedia.org/wiki/Observable_universe I got the approximate mass to be 3x10^52kg. After that it was just a...

So we know that Alice can free fall through the event horizon of a black hole and not notice anything. Yet Passing the event horizon is a one way event; no thing and no information can ever exit. (Except Hawking radiation). As a thought experiment, suppose we bombard the black hole with...

since energy absorbed by a BH is no longer available to the universe, why is that not a violation of the principle of conservation of energy?

I'm certainly no scientist, but I've always had an interest in Physics & Astronomy, so I read a bit here and there, watch primarily science shows on TV etc...Just an interest. I was wondering though, and figured on a site called "Physics Forums" there may be a physicist or two running around...

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...

What happens when a black hole devours another black hole? The bigger eats the smaller and increases in mass and size? What happens with the singularities?

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...

Much of what people say about the vicinity of black holes doesn't seem to make sense. For instance, it seems to be impossible for a black hole to grow by "ingestion" by scooping up matter around it or in its path, at least in the traditional sense. Gravitational time dilation takes care of...

Hi. If the hawking radiation is emitted from outside the event horizon , because probably that's the last place where the particles are being able to escape, then how come huge black holes ever evaporate as the matter behind event horizon has no chance of escaping in any way as to the immense...

Hello All, It says that, if we discover every galaxy, then there is a super massive black hole, present in each galactic centre. Is there any physical rule for that? I mean to say, a galaxy rotates with x,y,z...rules, the gravitational force is such and such... So, the formation of...

I was reading an article the other day about the second largest black hole found, something around 17 billion solar masses big, with an estimated event horizon 11 times the orbit of Neptune and it got me thinking. If all the matter generating the gravity lies in the singularity, how does that...

You have this loop of water (or some other "incompressible" fluid) with a nuclear powered water pump that constantly pumps the water in a circle. This loop is slowly lowered near the event horizon of a black hole, let's even make it a super duper massive black hole to minimize tidal effects...

Lets say an electron crosses the event horizon of a black hole. Now as it starts speeding up when it gets closer to the center of the black hole its B field will increase. Does this increased B field exist outside the event horizon?

Hello all . Why photon increase energy and frequency when falls in gravitational field ? or decrease it's energy when escape from a black hole ?

Are Finkelstein/Kruskal interior black hole solutions compatible with Einstein's GR? This topic is a spin-off from a number of recent discussions: "Are "flowing space" models compatible with GR?" "Schwartzchild and Synge once again" "Oppenheimer-Snyder model of star collapse" "Notions of...

'Over-massive" galactic black hole discovered http://www.nature.com/nature/journal/v491/n7426/full/nature11592.html Can someone elaborate on how this challenges current theories of galactic evolution?

Say a three solar mass black hole. Would someone notice it before it reached the Kuiper Belt, or only after there were deflections of known bodies in the Kuiper Belt?

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...

Why exactly is it necessary for angular momentum to be lost by a mass if it is to accrete around a black hole? the mass is decreasing its radius, so it speeds up: thus angular mometum is conserved. But everywhere it is saying that 99.99% of the angular momentum must be shed for accretion to...

Could a small black hole achieve an angular velocity such that the centripetal force is >= gravity, which would expand it enough to turn into a quark star or neutron star? I realize that in order to rotate the black hole further, more mass must be added that will increase the amount of...