Hole Definition and 1000 Threads

The question is probably naive, but please don't block this thread before I get an answer... As far as I know, mass doesn't exist by itself, it is rather an "attribute" of matter or, let's say it is attached to particles...no particle = no matter = no mass. Now, inside a black hole...

It seemed to have been asked before, but I am still a bit confused. How is the velocity dispersion formed? Doesn't the evidence of dark matter tells us that the orbital speed is uniform in a galaxy? Is there a direction of dispersion? (e. g velocity gets larger to the core) And why does...

I assume that, via scattering processes, the speed of light slows from that in a vacuum close to the centre of a black hole to zero at the event horizon. How is the gradient in its speed defined throughout this volume? Is an analogy with a sound wave reaching an interface appropriate?

Earth will not fall into sun because it has inertia, keeping it in orbit. Even if it suddenly loses some inertia, it falls to a lower orbit and won't fall into the sun, as its inertia increase again due to conservation of angular momentum. So, if a thing fall near a black hole, shouldn't it make...

Since gravity is stronger the closer you get to center mass, is it possible some neutron stars have a black hole inside?

Its thought that nothing can escape a black hole (correct me if I'm wrong) but what happens when a larger black hole eats a smaller one? Could there be a instance in time where matter was torn out of the smaller black hole, past its event horizon and into the bigger one? Thanks!

What are black holes made of?

Is a black hole a hole? What I mean by that, the word hole implies a structure that is shall we say like a plug hole in a sink. But a B/H is the result of an imploding star so surely it would be spherical. So really we are talking about black spheres which make much more sense in my head, also...

Hello, I have a somewhat dumb question. It is based on the fact that I can create a small vacuum in my mouth to move that "string" of spagetti into my mouth. I know it is possible, but I do not understand how spaghetti is possible to suck in if the shape is even and round like a "piston". I...

I’ve heard that the black holes that merged together and were the source that triggered gravity wave detector, have lost three solar masses. I understand to a very limited degree the basic notion of energy conversion like is the case in nuclear fusion/fission, annihilation, chemical energy...

Homework Statement A long (infinite) wire (cylindrical conductor of radius R, whose axis coincides with the z axis carries a uniformly distributed current I in the +z direction. A cylindrical hole is drilled out of the conductor, parallel to the z axis, (see figure above for geometry). The...

Homework Statement Lisa makes a hole in aluminum foil. She wants to know the diameter of the hole. She points a laser through the hole. That picture is what appears on the wall that is 1,25 meters behind the aluminum. the distance between every circle is 8mm. the wave length is 633nm...

I have a doubt about black holes. (I'm sorrying for my poor English.): 1 - Does an observer outside a black hole see forever (i.e. his lifetime) a object stationary when it reaches the event horizon? 2 - Or photons emitted by the object have its wavelength so red-shifted that the observer...

Homework Statement This is what the question looks like and I don't even have an idea where to begin since we didn't really cover this during lectures. Homework Equations This is all I have from my notes: also I found that Eg=Ec-Ev Any help appreciated Thanks

Once I cross the event horizon of a BH, is it valid to say that I'm at rest and the singularity comes up to meet me?

I know that string theory is not the flavor of the month, but the fuzzball idea circumvents the singularity which i think is a possible step forwards, is there any other theory that replaces the black hole singularity? https://en.wikipedia.org/wiki/Fuzzball_(string_theory)

As the tittle says, what is the mass of a black hole made of? Would it be made of the neutrons (and protons, electrons) that formed the earlier star? If no, what happens to those particles? Where do they go to after the black hole is formed?

In Hawking's "Black hole explosions?" 1974 letter to Nature, he states: My question is: wouldn't it be a terrible idea to generate a black hole of any size in a particle accelerator? http://www.nature.com/nature/journal/v248/n5443/abs/248030a0.html

If we were to take a microwave picture of a region of space said to have a black hole, would we be able to spot the black hole? Would we see a cold spot surrounded by a more hotter background?

So I have been watching COSMOS of late and in the 4th (I think) episode it states the possibility that other universes exist inside of black holes. I am aware of the immense strength of a black hole's gravitational pull so my question is this: Is there a material strong enough to resist it and...

I was reading about the pressure which is created when fermions are close of each other like in an electron gas, and I started thinking about what causes a black hole to form. Firstly, what happens when two fermions are forced to occupy the same place (and state)? By the exclusion principle I...

Homework Statement Metal cylinder of radius a has the z-axis as its symmetry. It has magnetic field at any point P as: $$B[x,y,z] = \frac{1}{2} \mu_0 J_z [-ye_x + xe_y]$$ A cylindrical hole of radius b which is displaced from the cylinder's axis by d in the x direction. The magnetic field...

Homework Statement A cylindrical conductor of radius ##a## has a hole of radius ##b## and there is a current ##i## uniformly spread inside the conductor. Calculate the magnetic energy of the conductor. Homework Equations $$U_{m}=\int_{Volume} \frac{B^2}{2 \mu_0} dV$$ The Attempt at a...

I have a story where an extremely advanced species has figured out how to produce and control kugelblitzes to a high enough degree that they can calculate the distance to an enemy and produce and fire one to explode at the target. Would there be any possible defense against such a weapon? I...

Hello everyone, I have a homework question for general relativity that is driving me nuts. It goes like this: An observer falls from rest at radius 10GM in the spacetime of a black-hole of mass M (in natural units). What time does it take for them to travel from a radius of 6GM to 4GM...

Homework Statement I'm taking a module in Solid State Electronics and in the first chapter we went through energy band diagrams, conduction band, valence band, fermi energy level, forbidden gap, etc. Now in the notes it starts to derive some formulae for electron and hole current densities Jn...

Having discussed recently https://www.physicsforums.com/threads/rod-falling-radially-towards-the-center-of-a-mass.871169/ I'm now puzzled by the question, what happens to the rod during his radial fall through the event horizon and what would the hypothetical observer at ##r=2M## measure...

Hi! We have a projekt at the university and I have been thinking of creating a tiny tiny black hole after I've read some articles. I know one can create an artificial black hole with polarized laser pulses at a block of glass. And then one can measure a lot of things, usually hawkingradiation...

Homework Statement Edit: Thanks to gneill for showing me the LaTeX ropes. Equations should work now. A perfect gas enclosed within a container escapes into vacuum through a small circular hole. The particle flux through the hole is ##\frac{nc}{4}## and the energy per particle escaping can be...

Say I have a solid sphere of mass on a horizontal surface. If suddenly there was a spherical hole(shape of a sphere) off center, will the sphere suddenly move? And there is no friction between the ground and the sphere. I'm assuming that it will. But my reasoning is this, the sphere suddenly...

Homework Statement A long copper rod 8 cm in diameter has an off-center cylindrical hole 4 cm in diameter down its full length. This conductor carries a current of 900 amps flowing in the direction “into the paper.” What is the direction, and strength in tesla, of the magnetic field at the...

I get that if you drop a tennis ball and a 10 lb medicine ball from the top of a tower they will both reach the ground at the same time. But what if I dropped a softball and a black hole with the radius of a softball (and the mass of a small planet)? Wouldn't the tremendous gravity of the black...

What happens to the Singularity when a Black Evaporates out of existence?

One of the enemies of SGI is the Ori, how does their black hole drive work?

Homework Statement sam makes a punch hole with the perforater( two holes ). She presses the lever at A down with a force of 40 N. Calculate the total force which a single pin presses on the paper. Homework Equations http://s6.postimg.org/yx62wbild/image.png The Attempt at a Solution would it...

Hello, Given: A large pressurized container with a small hole in a side. The sides of the container are VERY thin such that the thickness of the sides can be ignored. The pressure difference between the container and the environment is not large enough to result in choked flow. The outflow...

If the Earth were hollow and we only had the shell could a black hole at the center take the place of all the mass and provide us with gravity to keep us from floating away?

If a rod is in compression, will the minimum area on rod ( the section where there is a hole for pin) stress free? What if the rod is in tension? The rod BC is in compression and the boom AB is in tension? http://imgur.com/a/6asfB

According to this video, , if a black hole is large enough you could actually travel for some time within the event horizon without dying because the event horizon is so far from the actual singularity. So, assuming that's true, what would you see while you were inside the black hole? Here's...

So I need to use pigeon hole theory to solve these problems: 3. A man has 10 black socks, 11 brown socks and 12 blue socks in a drawer. He isn’t a morning person, so every morning he just reaches in and pulls out socks until he gets two that match. a. Use the generalized pigeonhole principle...

I know that the accretion disk of a black hole gets hot enough for powerful emission of x-rays, but does that disk get hot enough for certain elements to fuse?

I refer to a Schwarzschild Black Hole as the simplest example, and a well defined time outside the hole, say the Schwarzschild time. The information paradox of BH deals with the question of what stuff has fallen into the hole, but I am not aware that it deals with the question when the...

What if our quantum eraser was a black hole? There's talk of event horizons preserving all the information that crosses them? Could we test this hypothesis by seeing whether or not black holes make good quantum erasers? Depending on the distance to the black hole - it might be hundreds...

Hi I hope this is the right place for this questions, I started to think about this several years ago but had has a hard time finding anyone that's been interested in discussing this. As far as I understand time travel is not ruled out by modern physics at least if you limit yourself to go into...

If not why does the event horizon grow as more matter falls in?

Hey everyone, I'm new to physics forums and I would really like some help with my physics report. For my high school physics topic I have chosen an experiment where holes with differing diameters are drilled into the centre of the bottom of PVC pipe caps and the time taken for the each cap to...

Homework Statement A point source of light (wavelength \lambda = 600 \, \text{nm} ) is located a distance x = 10\,\text{m} away from an opaque screen with a small circular hole of radius b. A very small photodiode is moved on an axis from very far away toward the screen. The first...

Homework Statement Here http://imgur.com/a/4LRM6 2. Homework Equations The equation is given int he questionThe Attempt at a Solution gas will stop flowing when the pressure inside the gas is equal to that of the surroundings. I calculated the final mass of gas inside the cube. Then i...

The Schwarzschild Metric (with ##c=1##), $$ds^2 = -\Big(1-\frac{2GM}{r}\Big)dt^2+\Big(1-\frac{2GM}{r}\Big)^{-1}dr^2+r^2d\Omega^2$$ can be adjusted to a form involving three rectangular coordinates ##x##, ##y##, and ##z##: $$ds^2 =...

Near a black hole spacetime gets contracted, more and more as we get closer to it. At the event horizon the contraction (pull of spacetime towards the singularity) equals the speed of light, we could say that space is falling into the black hole at precisely the same rate as light trying to...