Black hole Definition and 999 Threads

General relativity passes test at Milky Way’s central black hole by Ken Croswell For the first time, astronomers use stars orbiting a supermassive black hole to test Einstein's general theory of relativity, finding no sign of a fifth fundamental force. Links: John Batchelor Show...

This question is based on page 71 of Thomas Hartman's notes on Quantum Gravity and Black Holes (http://www.hartmanhep.net/topics2015/gravity-lectures.pdf). The Euclidean Schwarzschild black hole $$ds^{2} = \left(1-\frac{2M}{r}\right)d\tau^{2} + \frac{dr^{2}}{1-\frac{2M}{r}} +...

I get how to derive black hole equations mathematically. But conceptually, how does it make sense that the radius of a black hole is 2MG/c^2, for example?

https://en.wikipedia.org/wiki/Gravitational_lens I want to know about bending light property of a black hole. The bending angle formula does not tell that r is perpendicular distance to light. Does a black hole having mass M has different bending power than the body having the same mass M...

I joined this site because I had questions and wanted to discuss topics on the subject of black holes. Lenny Susskind's lecture of this topic raised quite a few question a and ideas in my mind. I did write my concerns in the comments for the video, but I'll just paste that here as well. Here's...

The Kerr metric for a black hole of mass ##M## and angular momentum ##J = aM## is $$ds^{2} = - \frac{\Delta(r)}{\rho^{2}}(dt-a\sin^{2}\theta d\phi)^{2} + \frac{\rho^{2}}{\Delta(r)}dr^{2} + \rho^{2} d\theta^{2} + \frac{1}{\rho^{2}}\sin^{2}\theta (adt - (r^{2}+a^{2}) d\phi)^{2},$$ where...

Consider the Reissner-Nordstrom metric for a black hole: $$ds^{2} = - f(r)dt^{2} + \frac{dr^{2}}{f(r)} + r^{2}d\Omega_{2}^{2},$$ where $$f(r) = 1-\frac{2M}{r}+\frac{Q^{2}}{r^{2}}.$$ We can write $$f(r) = \frac{1}{r^{2}}(r-r_{+})(r-r_{-}), \qquad r_{\pm} = M \pm \sqrt{M^{2}-Q^{2}}.$$ Then...

Reading some of the recent info on black holes and how they ingest gas matter including stellar material... why doesn't dark matter be absorbed into the black hole and according to the article dark matter is part of black hole formation...

Hi there guys, Currently writing and comparing two separate Mathematica scripts which can be found here and also here. The first one I've slightly modified to suit my needs and the second one is meant to reproduce the same results. Both scripts are attempting to simulate the trajectory of a...

We often hear about string theory requiring extra dimensions over and above our 4D spacetime. Does this shed any light on the singularity which is supposed to exist at the centre of a black hole? Does our normal spacetime simply join the other dimensions in their hidden (curled-up) form? This...

Hi. I saw this: https://www.forbes.com/sites/startswithabang/2017/05/29/surprise-the-universe-has-a-third-way-to-form-black-holes/#52d7225f216d suggesting they saw a star undergo a "direct collapse" to a black hole with no supernova. Now this seems like it could be sensible -- if there's...

When they talk about information falling into a black hole, are they referring to the basic defining parameters of the particles falling into the hole?

What happens to the information entering to the Black hole??

Hi, Physics Forum! I've been wondering what would happen in the following thought experiment. I am not physicist and may have made some incorrect assumptions. Please explain if any of these assumptions are wrong. What would happen if you threw a piece of (very long and strong) rope into a...

If you shrunk an atom down to a certain point would it become a black hole like all matter in the universe can? How big would it be?

Yes I know. Sounds silly. I'm not a physicist, but it occurred to me to wonder: is it possible Earth is a black hole with data encoded in two dimensions on its surface? What would the proofs look like? Discuss.

Let's say that I'm hovering using a jetpack at a fixed distance above the event horizon of a black hole. And that I'm perfectly well shielded from any radiation and whatnot. Its a supermassive black hole with a super large Schwarzschild radius, so tidal forces are minimal. Approximately how...

Is this a realistic solution to the black hole singularity problem, Going beyond that, neutrino stars?

LIGO is reputed to have detected gravitational waves from the merger of 2 black holes (BHs). For an external observer of such an event, each BH would appear to approach the event horizon of the other, but never cross it in a finite time...is this correct so far? But the event horizons are...

Einstein's general theory of relativity describes the stars distort spacetime fabric and it appears a black hole makes a hole in the spacetime fabric. It is evident that the size of a galaxy does not change due to gravity but in large scale the distance between two distant galaxies increases due...

Consider the following two definitions of the surface gravity of a black hole (taken from page 23 of Thomas Hartman's lecture notes(http://www.hartmanhep.net/topics2015/) on Quantum Gravity): 1. The surface gravity is the acceleration due to gravity near the horizon (which goes to infinity)...

I wonder, what would happen if you started dropping lots of electrons into an existing black hole which otherwise doesn't accrete any new matter? The charge of the black hole would build up much faster than the mass. Wouldn't its charge become so high at one point that further electrons would...

I recently studied about black holes and hiw they attract light too. But does light have mass? If it doesn't, I don't see any way how gravitational forces affect light. I have heard a bit about wave particle duality. But could you make it more clearer? I have no idea of relativity or particle...

If I fall into a Schwarzschild black hole and, as I'm falling, look in the direction away from it, what do I see? I once heard someone say the rest of the universe would appear to move faster and faster, and as I cross the event horizon it would appear to move infinitely fast. I'm not sure...

Hi, is anyone familiar with topological insulator? I read an interesting paper: http://arxiv.org/abs/1703.09365, Black hole as topological insulator Abstract: Black holes are extraordinary massive objects which can be described classically by general relativity, and topological insulators are...

If space were like a ocean of ice chunks where everything gradually moves apart and the andromeda galaxy and our galaxy are moving closer to one another. Finding the connection point would find a black hole right. Or is that not possible with the way space moves?

Hello to everyone! I am trying to understand in practice the Gravitational Time Dilation by calculating the time distortion near the supermassive black hole Sgr A* in our Galactic Center. According to Einstein's Theory of General Relativity, the time distortion near a black hole is calculated...

Assuming a wormhole exists, what would happen if one took one end of the wormhole into a black hole. Could they enter the wormhole and leave the black hole? What would be the result if they did?

How and if singularity is related to Plank size (h) , are they be related ? If they are; can the singularity have squared shape (like pixel) , if it is h size so that is the "smallest" understand by "physics" and any curve (circle) would break the rule of h begin the smallest ? Does my question...

After a quick and not fruitful Google Search I leave this question in better minds than my own. Q- Has there been any discussion linking the start of our Universe with a black hole? <Reason behind Question> I feel as if certain phenomenon seems quite similar to one another. A) star dies...

I was thinking about the title but after searching Arxiv, PF and the internet in general, my confusion has only increased. I have a few questions: 1. Often I see units where ##G=c=\hbar=1##, but what is the charge of an electron in these units? Everyone says M=Q as if it was somehow obvious how...

Homework Statement To what radius do you need to compress Mars in order to turn it into a black hole? Homework Equations None given, but I am mildly familiar with Schwarzschild and his equation. I know that if we double the object's mass, multiply by the universal gravitational constant, and...

What is the name for the "stuff" (neither matter nor neutrons) at the heart of a black hole?

Assume an eternal, static black hole which has an event horizon, a spherical surface at which any object passes a point of no return and is condemned to move toward a mathematical singularity. One of the predictions of being inside a black hole is that every spatial direction points towards the...

A black hole is basically extremely dense matter. What could happen if it interacted with antimatter? I guess a part of the black hole's mass would annihilate.

Is it possible for a photon to be so energetic that it forms a black hole? If so, how fast would that black hole be moving?

Ignoring for the moment the plausibility of this scenario, what would happen? A black hole is the ultimate gravity well, right? In some circles, they're even considered tears in the fabric of the universe. So what would happen to that fabric if you moved the black hole? Would it behave like...

I have seen at many places that if ever matter travels more faster than light, it's relativistic mass will reach nearly infinity. Some says it's the inertia, so very high energy is required to accelerate. But since it is traveling with the velocity above 3×10^8 m/s, i believe that the high...

I realize that this question has been asked many times on this forum, however, I have yet to come across a satisfying/understandable answer that takes into account gravitational time dilation. Premise: The speed of light inside a gravitational field is slowed down relative to a distant observer...

Homework Statement From the homework: In General Relativity it is found that the radial equation of an object orbiting a non-rotating black hole has the form $$\dot r^2 + (1 - 2 \frac {V_o} {r} ) (\frac {l^2} {r^2} + 1) = E^2$$ where ##r## is the radial coordinate, ##l## is the angular...

Ok..I know that at some point, from the Hubble Law , galaxies will seem to moving away from us speed of light,But actaully they can't because the space-time itself expands so it will be like a black hole horizon,which within that radius its , c/H , we can observe things etc.But out of that...

Homework Statement For school I'm doing a project on hawking radiaton but I have very big difficulties trying to understand it. I'm trying to understand the matter about: Unruh effect, particle pair (antimatter - matter) and the theory of relativity regarding vaccuum. Homework Equations none...

Hey guys, Does black holes exist? Is it even real?

Hi everyone, I was thinking of a new theory in physics regarding dark energy, black holes and the accelerating expanding universe. What if most of the matter created by the Big Bang was pushed at the edge of the new created space/time like explosions, the matter is at the edge of the explosion...

I am an undergraduate student of a university, I have taken the research topic as Study of Rotating black holes and Hawking radiation which I am really interested. Research description as follows. The geometric invariant are computed in various black hole geometries in several different...

Forgetting about the singularity for the moment, is the interior of a black hole a space-like region? That is, are any two events that occcur past the black hole horizon space-like separated? Thanks in advance.

Homework Statement I want to calculate the on shell action for the case of a AdS Schwarzschild black hole. Homework Equations Following the case of the flat Schwarzschild black hole I tried to add a counter-term of the type of a Gibbons-Hawking boundary term for flat Minkowski spacetime...

why can't a photon escape a black hole? i think it is because the photon is red shifted away to nothing, if this is true, it would be possible to create a photon that would be energetic enough that a black hole would not have enough time to red shift it away to nothing, unless there is some...

why can't a photon escape a black hole? i think it is because the photon is red shifted away to nothing, if this is true, it would be possible to create a photon that would be energetic enough that a black hole would not have enough time to red shift it away to nothing, unless there is some...

I'm sure that there are limits to the analogy between the event horizon of black holes and the "Rindler horizon" for an accelerated observer, but there are a number of similarities: For Schwarzschild spacetime as described in Schwarzschild coordinates: Spacetime is static, and a rocket must...