Hole Definition and 1000 Threads

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?

Homework Statement A solid is generated by revolving the region bounded by y = x2/2 and y = 2 around the y-axis. A hole, centered along the axis of revolution, is drilled through this solid so that one-fourth of the volume is removed. Find the diameter of the hole.The Attempt at a Solution...

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...

I am a bit wary about posting this, as I am pretty sure what the response would be if I claimed this was paranormal or some other weird stuff. So before we start, I do not believe in ghosts, I do not follow religion, I am very much a believer in the scientific method. I am not claiming to have...

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...

Homework Statement A flexible chain of mass M and length L lies on a frictionless table, with a very short portion of its length L0 hanging through a hole. Initially the chain is at rest. Find a general equation for y(t), the length of chain through the hole, as a function of time. (Hint: Use...

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...

Homework Statement A very long, solid insulating cylinder with radius "R" has a cylindrical hole with radius "a" bored along its entire length. The solid material of the cylinder has a uniform volume charge density "ρ". In this problem, you will find the magnitude and the direction of the...

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...

Hi! I try to figure out the probability (sure as function of parameter time) of transition particle in the hole from the first excitation state to the base state in an infinity potential hole. Because the eigenfuncion of particle there are orthogonal, the probability looks like zero -...

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...

Charged Sphere with a Hole -- Check my work? Homework Statement You have a spherical shell of radius a and charge Q. Your sphere is uniformly charged except for the region where θ<= 1° (which has σ = 0). Imagine that your field point is somewhere on the positive z-axis (so z could be...

Hi all, I just did an exercice and there is one point that I don't understand (about Ampere's law). Homework Statement The exercice was about a cable with given diameter a, in which a small hole with diameter b is drilled in. The axis of the cable and the hole are parallel and the...

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...

Homework Statement Find volume of a sphere with radius R with a hole drilled through the center of radius b. (b<R) Homework Equations cos thera = adj / hyp The Attempt at a Solution [SIZE="5"]4\,\int _{0}^{\arccos \left( {\frac {b}{R}} \right) }\!\int _{0}^{\pi }\!\int...

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...

Time for Droplet of Water to Fall .25m from Hole Homework Statement A cylindrical tank .7m tall is filled with water and placed on a stand (below it) that is .3m tall. A hole of radius .001 m in the bottom of tank is opened. Water then flows through the hole and through an opening in...

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...

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...

there is a similar case here :https://www.physicsforums.com/showthread.php?t=296966 so I've tried it and what i did was to equate both individual moment of inertia about z axis (and later applied parallel axis theorm) with negative mass for hole. added both these and found out Ix = M/4...

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...

Hi everybody, I'm looking for a way to determine the maximum moment of a uniformly loaded circular plate (diameter = 10") with eccentric circular hole (diameter = 4"). The plate is clamped at outer edge and free at inner edge. The ultimate objectif is to determine the minimum thickness of...