Hole Definition and 1000 Threads

Would a black hole whose density is lower than that of water, sink? The answer is likely over my head. So far, I've found 5 answers by "experts", with quite different opinions. For instance on this website, one reads . On IRC I was told by another expert that it would sink. Here are the...

Can a black hole be presented as a Heegaard decomposition or as the complement of a knot? I'll try and elaborate: If I understand correctly, the cross section of spacetime near a black hole can be thought of topologically as a manifold. What manifold is it? Can the manifold be decomposed?

Hi, I have the following problem: Given the 5-D generalization of the Schwarszschild solution with line element: ds^2=-\Bigg(1-\frac{r^2_+}{r^2}\Bigg)dt^2+\Bigg(1-\frac{r^2_+}{r^2}\Bigg)^{-1}dr^2+r^2[d\chi^2+\sin^2(\chi)(d\theta^2+\sin^2(\theta)d\phi^2)] where ##r_+## is a positive constant...

Please forgive the awkward title. "Supermassive black hole" uses up a lot of the title character limit. Has anyone made a simulation of what would happen if a neutron star impacted a simplified (Schwarzschild) supermassive black hole? I've seen simulations of a neutron star colliding with a...

How much is a circular pipe with holes in its walls weaker than a pipe without holes, specifically when subject to bending and torsional forces? Say I have a hardened steel pipe of some diameter, length and width, and a hole (of max 1/5 the pipe diameter) is drilled horizontally, through both...

Is there a fundamental difference between the (speculative) understanding of a singularity arising from the creation of a black hole and the singularity which we think may have been at the origin of the Big Bang? Noteably, would there be two basic theoretical types of singularities...

Can a "thing" go through the event horizon of a black hole? I mean, everything inside a black hole can travel only in one direction: inward. That destroys the "thing" itself, since independent parts of the "thing" are no longer connected to one each others. Perhaps it's impossible for a "thing"...

Found this interesting interactive experiment. http://hubblesite.org/explore_astronomy/black_holes/encyc_mod3_q14.html In the interactive, it looks like the black hole is orbiting around something. What would it orbit around? Or am I looking at it wrong?

Let us imagine a photon circling around a black hole, as the picture shows. The gravity of the black hole curves the movement path of the photon into the shape of a circle. From point 0, geometric points A and B appear simultaneously with the photon, each in its own direction. The points travel...

According to Einstien's theory of evolution, the closer to the speed of light that an object travels, the slower it appears to move to an outside observer. (see https://www.thenakedscientists.com/forum/index.php?topic=40951.0) To take this to the next step once an object crosses the event...

What is the difference between mathematical singularity and black hole singularity[emoji780]

I'm trying to find how much energy will radiate when an object fell in a black hole. Is my calculations are correct or I'd committed mistake somewhere?

Greg Bernhardt submitted a new PF Insights post Calculating the Spin of Black Hole Sagittarius A* Continue reading the Original PF Insights Post.

I'm reading Lambourne's <Relativity, Gravitation and Cosmology>, and I cannot get a result the book describes. It's on equation (6.7) in 173p. When a person free-falls into a non-rotating black hole from ##r=r_0## to some position ##r=r'##, the proper time becomes...

I having difficulty wrapping my head around a concept that I wish to solve. I have a 10L tank of compressed air at 100psi. When an outlet hole of cross-sectional area of 0.115 in^2 is opened, I wish to develop a curve of pressure vs. time from t=0 until pressure drops to atmospheric. Many things...

well since gravity waves are supposed to have mass, they are supposed to be effected by gravity itself, and :/ how are we supposed to detect gravitational waves emitted from a black hole when none can get out?

How come the gravity of a stellar- mass black hole is strong enough to trap light but the gravity of a stellar-mass star (eg the sun) is not strong enough to trap light ?

What is the condition for a spherically symmetric solution represents a black hole? ##ds^2=\exp(\nu(r))dt^2-\mu(r)^{-1}dr^2-r^2 d\Omega^2## it is enough that it is fulfilled that ##\nu## and ##\mu## are nulled in the same value of r??. There are other conditions?

Its pretty tough to calculate the entire mass and weight of entire black hole.But how we will give a approximate value? How we will calculate its mass and weight? Could you list some stuffs that caught into the black hole? Has any scientist ever visited a black hole and collected data on it...

Thought experiment: single use of "magic" Setup: Let's assume we have a giant ball of water in space. Magic: Let's assume the water does not compress its center under its own gravity. (Constant density of 1 g/cm^3) Basic stuff: The mass of this ball of water, (since it does not compress)...

A star or a planet is a material object, while a black hole is an 'immaterial' spacetime object. Does the material or 'immaterial' nature of an object make any difference in how it curves or travels through spacetime as it manifests gravitation (apart from the powerful gravitation near a black...

Dear All Concerns Black Hole is formed at the end of life of a big star. The mass of such star should be equal to 5-10 solar masses. But I am imaging very small moving black hole coming to our solar system and passing between our Earth planet and the sun thereby creating solar eclipse of unique...

I read somewhere that it is not possible to prove that Our universe (from big bang to now) have different principles that inside of black hole. I think that one physicist said something like this. Or in different words: are principles of our universe different as inside of a black hole?

Consider a meter stick sliding along its length towards a hole which is a meter wide in the direction of motion. Suppose the meter stick moves with speed so that the gamma factor is 10. Then in the stick’s frame, the hole is 10cm and should be easy to cross. But in the hole’s frame, the stick...

Could a particle near a black hole about to enter rid the string of its vibration?

Homework Statement [/B] An uncharged nonconductive hollow sphere of radius 10.0 cm surrounds a 20.0 µC charge located at the origin of a cartesian coordinate system. A drill with a radius of 1.00 mm is aligned along the z axis, and a hole is drilled in the sphere. Calculate the electric flux...

If this is true where is the core of that star, either a neutron star or a black hole should exist near by, right?

Greetings, I've been thinking about the escape velocity having to be greater than c inside the event horizon for a particle to escape. Since this cannot happen, I picture the matter at the core as an insanely dense ball of atoms. But, could the pressure be so intense that atoms cannot hold such...

Hello everyone, "Does a charged particle radiate in free-fall?". I read many threads on this subject and I was surprised to find out that there is no unanimous "Yes or No" answer to this question. Here is an interesting answer from researchgate.net: The question is widely discussed in the...

What would spacetime look like near a black hole that was rotating at its extremal speed and had a ring of matter orbiting it at ultra-relativistic speeds (just outside the photon sphere), such that the ring was orbiting in the same direction as the black hole’s rotation? The ring would add to...

Homework Statement Suppose there is solute ##s## in a bowel containing fluid. There is a tiny hole near the bottom which leaks a small fixed volume of solute ##\lambda## per unit time ##dt##. In addition, there is a small added solute to the fluid in a constant rate ##\alpha## so as the volume...

Hi everyone, I was wondering how to best calculate the breakage resistance of a drill hole which is being flowed through with a certain volumetric throughput within a polycarbonate (PC) rectangular plate. Well basically, the breakage resistance of the PC around the drill hole :) The plate is...

Assume a source of EM radiation at wave length λ hits a barrier with a small circular hole of diameter d << λ. What fraction of the radiated power (watts) that hits the hole passes through it? Does it depend on the thickness of the barrier? I understand that after passing through the hole, the...

So the Hawking radiation and the flinging of matter from the black hole, could this explain where all the matter goes? I am unsure of the theory for the second one, but if matter is broken to its quantum particles then why can't those quantum particles be in the Hawking radiation. Still very...

In simplified terms Hawking Radiation exists, because in the vacuum surrounding a black hole these subatomic-particle-pairs pop into existence and one of these particles manages to escape from the black hole. This stream of escaping particles is called Hawking Radiation, right?(Please correct...

Homework Statement A solid is generated by revolving region bounded by y=(1/2)x^2 and y=12 about the y axis. A hole centered along the axis of revolution is drilled through this solid so that 1/4 of the volume is removed. find the diameter of the hole. Homework Equations y=(1/12)x^2 y = 12...

Articles refer to white holes being associated with dark energy. What if dark energy is a larger version of the following process? Black holes banish matter into cosmic voids Some of the matter falling towards the [supermassive black] holes is converted into energy. This energy is delivered to...

How should we deal with the fact that GR predicts light not scaping from a BH while QM states BHs radiate?

Leonard Susskind said "everything that ever fell in, to make the black hole, [..] [is] all contained in [...] progressively thinner and thinner shells that approach the horizon asymptotically, never quite getting there" and from the perspective of someone outside the black hole "a shell, called...

Homework Statement We have a circle of radius 4 with center at the origin of a referential, and a circle hole in it of radius 1 and center at (-2,0). We're supposed to calculate the center of mass. 2.MY QUESTION. I know, by the usual formulas for calculating center of mass I get 2/15 as the x...

If you were to condense an atom or group of atoms, the gravitational force would be very large because the atom is 99.9999999999996% empty, so making it 100% full would be like crushing a pound of tin foil into the size of a pen dot. If the density is so much it would make a huuuuge...

Suppose A is on a planet orbiting a black hole and B is far off such that due to time warp, every hour A experiences is equal to a year for B. Could they communicate using radio devices? Would an hour-long message from A be year-long for B? How much extra time it would take for a radio message...

Is it astronomically known what the closest distance is between Earth and a black hole? (I was not able to locate an answer to this question searching the Internet.) If not, the article https://www.sciencenews.org/article/we-share-milky-way-100-million-black-holes says The Milky Way teems...

Where do the static electric field lines appear to originate from a charged black hole, non rotating, Reissner–Nordström metric? I've had a number of qualified physicists say they appear to come from the center of the black hole, but people on these forums have said that doesn't make sense...

Say I have a simple 2 or 3mm thick sheet of plexiglass or aluminum, and I have a closed chamber box out of these sheets. Now, I want to build a pressure inside the chamber, but the prototype only has a simple O shaped "hole" on the box. I can choose the diameter of the hole, and I have a rubber...

I find a very interesting site that shows us what it would be like to travel to a black hole or a neutron star. https://apod.nasa.gov/htmltest/rjn_bht.html Have fun !

I hear people say that even light cannot escape from black hole.So how big is this black hole?Why gravitational pull is very high? Does it have any escape velocity like Earth have?

I've heard some explanations of the Black Hole firewall involving broken entanglement releasing energy that frankly I don't understand, but I have another way to think about it and I'd like to know if its even approximately correct. As I'm getting closer and closer to the Event Horizon time...

Hello, Here's an interesting question inspired by a homework probem (not mine), we know that circular orbit (for scjwarzchild black hole) exist only if L ≥ sqrt3 c Rsch=Lisco . Where does this inequality come from? do you have a lecture which can help me to understand? Thanks

So the title pretty much sums it up. I'm having a heated discussion on this topic with a friend so yes/no at the end would be nice :wink: