Black hole Definition and 999 Threads

Hi, According to Stephen Hawking, it is theoretically possible for black holes to emit radiation. How is this so? As I understand, please correct me if I'm wrong, it has to do with the creation of particle/antiparticle pairs. Are these particles generated as a result of the intense...

As we know, the gravitational pull of the black hole is too strong, not even light can escape from it... Let me assume 2 person: A and B A is sucked into a black hole while B is outside the event horizon... At first, B will notice that A has disappeared due to the lights(image) of A is...

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...

In another thread (on Oppenheimer-Snyder collapse), I posted a link to some lecture notes on gravitational collapse. Checking on the author, I find he is extremely prolific on many fundamental areas of GR (from the computational standpoint). Of particular interest...

the electron falls and emits radiation. will it lose all it's energy by the time it reaches the event horizon or will it have enough (>2m) to produce a particle shower? Will other things happen?

Hi there. 1. The problem statement I am asked to write the equations which give us the mass of a black hole as function the proper time. Homework Equations The Schwarzschild metrics is given by $$ ds^2=-(1- \frac{2GM}{r})dt^2+(1-\frac{2GM}{r})^{-1}dr^2+ r^2(d\theta^2+ \sin^2(\theta)...

I have not read any formal (mathematical) explanations of black hole thermodynamics, only popular literature on that subject. I have read that the total amount of information, and therefore its entropy, that a black hole can contain is proportional to the area of its event horizon (measured...

How close could a tachyon get to a black hole and still escape?

Hello all, Cosmic Variance just had a great post up about Black Holes, wherein they were talking about something called the firewall, located at the horizon. I gathered it was a result of the Unruh Effect + Hawking Radiation, and CV seemed to say that this would cause anyone passing the...

for example take two halves of a black hole as m1 and m2. since we told black hole has no volume so we take distance between the two halves as 0. by Newtons laws of gravitation the force of gravitation between the halves is infinite. that is the black hole can shrink the universe to a...

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...

Hey, The entropy of a black hole is S = kB (4∏GM2)/(hbar c) S=Q/T T= Q/S T = Q (hbar c)/ (4∏GM2kB) The temperature derived from hawking radiation is: T = c3 hbar/ (8 pi G M kB) Which implies Q = (1/2)M c2 Is this true? I have found online that the heat should equal...

hey guys, i'm working on this question to approximate the entropy of a black hole, the approximation is that for the maximum entropy to be obtained you need a maximum number of particles to create the black hole, the particles must have low energies - large wavelength photons, but the...

okay, this might be a very silly question but whatever. If a black hole were composed of antimatter, would we be able to tell? If the black hole were created by anti-matter collapsing and becoming dense enough to turn it into a black hole, then if regular matter fell into it, it wouldn't...

I am loving this forum :) I am troubled by the conventional image of space being inverted by a black hole - if that's the correct way to phrase it. But I'd like to take a step back and use a model to explain. We observe an enclosed room, shaped like a cube, with 1,000 cubic feet of space...

Hi everybody. I am well aware that there is only one black hole in 2+1, i.e., the BTZ one. I also know that for vanishing and positive cosmological constants we get solutions with a conical singularity. My question is more about the interpretation of these last results. Assume that in the BTZ...

Hi, I've been reading through Stephen Hawking's 'A Brief History of Time' and I have reached a section about how, contrary to popular belief, Black Hole's are not necessarily black since they emit photons outside the event horizon. I am wondering how they emit photons. Does it have to do...

This may sound very silly and a tad bit hard for me to explain, but here goes! I have experienced and seen how when a lit fire was covered with a container, the oxygen begins to dissipate and it begins to suck things into the space. (I did not light myself on fire!) So I was wondering if...

It's theorized that most black holes have rotational speed. Also, I'm guessing, event horizons are always spherical or close to spherical because they are a function of the gravity well extending from center mass of the black hole. My question is this, could a black hole ever rotate with such...

Friends, Acquaintances, and Juvenile Delinquents alike lend me your ears... As a thought experiment, let us say we have two photons, photon A and photon B. Now our two lovely quanta of electromagnetic radiation are special, because they have been entangled after an atomic cascade. After the...

There is a spaceship situated orbitting a black hole at x million miles. We have an exactly x milllion mile long string (perhaps a bit longer) Lets not call it a string, but a flexible steel cable instead. Now, we tie a metal ball at its one end, and project the ball towards the black hole...

Hypothetically, what would happen if a person was sucked into a black hole? Would they just simply die?

Does anyone know of a review article on astrophysical collapse to a black hole? There are several statements I've picked up from WP that either surprise me or that I'm not sure I understand. This Penrose diagram http://en.wikipedia.org/wiki/File:PENROSE2.PNG shows the singularity as being...

I see statements that in order to define a black hole, we need asymptotic flatness, but this only seems to be necessary because we want to define the horizon as the boundary of a region from which light can't escape to null infinity (\mathscr{I}^+). It seems like you can have a well defined null...

I know that a black hole creates infinite curvature in spacetime and hence infinite time dilation. I was wondering though, if I could think of this stopping of time due to the fact that a light ray moving radially towards the centre of a black hole would have to travel infinitely far along the...

I've seen it said somewhere that an observer falling into a black hole doesn't notice anything qualitatively unique at the exact moment they cross the event horizon. Does this include Hawking radiation? That radiation is described as being emitted by the event horizon, so once the observer...

How much mass would even the smallest of black holes have to absorb (keeping also in mind the radiation lost as it grows) to obtain its size? And considering the largest Black holes discovered so far, how much mass would it have had to gobble up to get to that size? On the average, how much...

Homework Statement Hi, From the Kerr metric, in geometrized units, \left(1 - \frac{2M}{r}\right) \left(\frac{dt}{d\lambda}\right)^2 + \frac{4Ma}{r} \frac{dt}{d\lambda}\frac{d\phi}{d\lambda} - \frac{r^2}{\Delta} \left(\frac{dr}{d\lambda}\right)^2 - R_a^2...

Hi all, I am trying to understand the process of Hawking radiation in the case of an eternal (static/everlasting) black hole. As a bit of background: i understand (semi-quantitatively) how one gets particles produced when one is a frame with constant acceleration. And I sort of understand...

I am trying to get my head round this problem but not having studied it I need some help.

I read an article yesterday about the fastest moving pulsar yet detected. The Chandra X-ray observatory spied a pulsar in SNR MSH 11-61A and IGR J11014-6103 moving at approximately 6 million miles an hour. This raised the question in my mind of what would happen if this pulsar were to collide...

hello all I am so glad to have found this forum. I've always had an interest in astrophysics, cosmology, SR/GR, etc, and no place to ask questions. I'm an engineer and was once a member of Mensa (I only left the organization because I thought other members were crazy. Sorry). So although I'm...

I know that in scenarios where QM and GR are both applicable the answerers come out ridiculous. I believe this may be one of those scenarios. It is also possible that I have some misunderstanding that leads to a ridiculous answer. My question is which of these is the case. A photon is...

Hey, In space missions why do they choose different frequencies for viewing stars? For example why do they choose both 43 GHz and 230 GHz to view a black hole? Cheers!

Can somebody help me out here. The gravity of a black hole is so strong that nothing can escape it, not even light. If that's the case, why can't another black hole of larger mass be used to extract information from the first black hole? Sort of like how a Siphon works. I imagine some sort...

Hi, Is Sagittarius A* the black hole a quasar or a blazar? As far as I've understood, AGNs are quasars, blazars or seyfert galaxies. Can someone please explain how the shockwaves/knots in the jets emitted by black holes can be detected?? Thanks :)

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...

Let's say I start out a few thousand kilometers from a black hole, and I begin to move toward the black hole due to it's gravitational pull. What type of time dilation would I experience as I fell into the black hole before the event horizon, and after the event horizon? By the time I die...

If a magnetar gets big enough to become a black hole, would said black hole have an intrinsic magnetic field beyond outside of its event horizon? Perhaps a better phrasing would be: can electric and/or magnetic fields escape a black hole, or is it just electromagnetic waves (and matter) that...

Is it feasible to perform space VLBI at 230 GHz? Also how does one detect the radio jets at 230 GHz?

I recently tried to calculate the mass of the black hole in the center of the milky way and it came out to 1.8x10e+53 kg, that can't be right, what's going on?

Electrons and protons have anti-particles. Has there ever been any speculation or work done on whether a black hole has an anti-particle such that if the two were to collide, they would annihilate each other? Probably not, but I was just curious.

So, does anyone have any thoughts on the papers recently published by Almheiri/Marolf/Polchinski/Sully (http://arxiv.org/pdf/1207.3123.pdf) and Susskind (http://arxiv.org/pdf/1207.4090.pdf)?

If we had a positive point charge of incredible quantity, does there exist an imaginary sphere about it, such that regardless of the initial speed and direction of any electron, that electron could not escape spiraling into the positive point charge? Conversely, regardless of the initial...

I know that because of the great gravity pulling at your feet much not as much at the upper half of your body you become like spaghetti but I want to know why this happens and what else could possibly happen.

Why is it generally acccepted that light can't escape from a black hole when gamma and radio wave radiation has been shown to be coming from them? A way I can think around this is that the expulsion happens before the event horizon and is some sort of rejection phenomenon that fuels a chain...

Let's use the classical example of a black hole: A massive planet that has shrunk tremendously, until the escape velocity at its surface is greater than the speed of light. If you were sitting on the surface of said planet, would it still be possible for you to escape? Let's say you had...

I have red that as an object approaches a black hole, to an observer the object never appears to pass the event horizon because of time dilation. If so why does the hole appear black, wouldn't the same thing happen to the light, and wouldn't it spread over the surface of the black hole...

't Hooft states that information going into a black hole actually ends up at the event horizon of the black hole, increasing the surface area equal to the amount of information absorbed (conservation of matter and energy). Our entire universe is postulated to be a 3 dimensional space projected...