Black holes Definition and 1000 Threads

The conventional picture We often describe two perspectives of infalling matter: Outside observers see the object asymptotically approach but never cross the horizon, with signals becoming increasingly redshifted The infalling object supposedly experiences a finite proper time to cross the...

I searched for this in the forum but apparently no one has asked this yet. So my question is, do black holes have magnetic fields and if so, does the magnetic field extend beyond the event horizon? I have a thought experiment in mind. Consider a neutron star, which has a very powerful magnetic...

Hello! I am a creator who loves the fascinating world of science. I enjoy exploring science from a unique angle, which often leads to new and creative ideas. While some of these ideas can be speculative and challenging to prove, I make sure they align with scientific principles and logical...

Posting this as I have so far not been able to find a straightforward answer to the following question. The formula for the outer event horizon of a kerr black hole is given by the following equation: $$r_+ = \frac{GM}{c^2}\left(1+\sqrt{1-\frac{J^2c^2}{M^4G^2}}\right)$$ Where ##J## is the...

If I understood it correctly, at enormous timescales into the future, it is theoretically expected that eventually stable massive structures (like white/black dwarfs) will suffer quantum tunneling events that would make small pieces of them slowly turn into black holes that would rapidly decay...

Hey guys! I'm excited to be a part of this community and can't wait to answer some questions and of course , ask some as well. I'm in the final year of my master's degree and currently working on primordial black holes and their candidacy for dark matter. Ad Astra per Aspera!

So a bit of context, I've been trying to model a plot of energy density relation for radiation and Primordial BH, but it is not right. Would someone be able to help me out? This is what I have so far. I am assuming the PBHs decay into a Planck relic, and the decay is instantaneous. Does the...

Does the interior coordinate patch of the Schwarzschild analytic extension really describe the interior of a black hole? After all, that portion would have mass. Also, is there a way to describe just a black hole’s with regular spherical coordinates?

If this post should be in another forum, please advise so I can post there instead. I hope I got the right prefix. Thank you. 1) Is it possible for Hawking Radiation to be dark matter, at least in part? Do the equations rule out this possibility? 2) Are Black Holes actually spinning or is our...

Hi all, As I understand it scientists have postulated that dark matter exists to explain the unexplained orbit of stars around the centre of our galaxy. The orbits not being as they should be by Newtonian or Einstein calculations. At the same time they postulate that there are perhaps 1000s of...

as I understand time stops at the event horizon of a black hole for the far away observer; so can we actually see 2 black holes orbiting eachother? I also understood that the singularity is a moment in future. so what happens when 2 black holes orbit eachother with the singularites? from the...

Do Black Holes have Singularities? "There is no proof that black holes contain singularities when they are generated by real physical bodies. Roger Penrose claimed sixty years ago that trapped surfaces inevitably lead to light rays of finite affine length (FALL's). Penrose and Stephen Hawking...

Where should the nearest black hole be? Something like 0.1% of stars end up as BH's, so that suggests about 100 million in the Milky Way. The easiest thing to do, instead of a complicated geometry problem, is to recognize that the cube root of 0.1% is 0.1, so that we expect BH's to have...

We've been talking in another thread about supermassive black holes. That has me thinking about really, really big BH's - so large that the spacetime curvature and evolution of the universe matters. Let's start by defining the density of a black hole as its mass divided by the volume enclosed...

Professor Brian Cox was on the TV last night. He stated that eventually everything will end up in black holes. When there is nothing left to absorb they will start evaporating via Hawking radiation until eventually they all disappear in a small flash of light and then there will be eternal...

A Kerr Black Hole (BH) is a spinning BH. There is an Event Horizon (EH) which is $$r_H^\pm = \frac{r_S \pm \sqrt{r_S^2 -4a^2}}{2}$$ where ##a=\frac{J}{Mc}## and ##r_S## is the Schwarzschild radius. My question is, suppose I'm in a spacecraft, not in orbit, but stationary at a distance ##r##. I...

I am trying to reproduce the results from this paper where they find out the expression for the Landau functional to be $$\psi(x,t,p)=\frac{1}{4}(\frac{1}{x}+6x+px^3-4tx^2)$$ We plot the Landau functional v/s the order parameter($x$) at $p=0.5$ and obtain the Figure 4. from the paper as Now...

Hello! I am a highschooler looking to learn more about physics and looking to hear a lot of feedback on my thoughts about physics.

Could an entangled particle (or larger entangled object), sent into a black hole, reveal anything new about black holes, with the connected entangled partner outside the black hole? Can entanglement escape the singularity and communicate with its partner? I've heard the singularity is a rip in...

It is said that accretion disk around compact objects like black hole can convert up to 40% of the mass of an infalling material into energy. This means, to my understanding, that if we throw 1kg of matter onto a BH through an accretion disk, during the accretion 0.4kg worth of energy in the...

Hey everyone, I'm brand new here! I absolutely love Physics, specifically Astrophysics, I'm actually looking to study black holes and stellar evolution. I'm preparing to go to University this fall to get my bachelors in Science with a major in Physics and a minor in either Mathematics or...

Black holes are everywhere in astrophysics. There are numerous discussion about how black holes look like, what happens to gas falling into black holes, how light bends around black holes, whether there is loss of information when mass or energy falls in, etc. There is thought to be a black hole...

This pop article popped up (isn't that what they do, by definition?) on my google news page. https://www.sciencenews.org/article/black-hole-paradoxes-quantum-states It claims that a thought experiment shows that doing a double-slit experiment near a black hole event horizon can reveal...

Hello everyone, Imagine the following situation: You are inside the events horizon of a static black hole (called BH1) Now, due to the bended space-time, your future points to be inside the event horizon until eternity (You will never be outside) Now, a second static black hole (BH2)...

The event horizon is an area where the curvature of space is so great that no particles from within the black hole may travel past that point. For analogy, it is as if a highway ramp curved all the way back to its point of origin, an automobile moving forward would just end up going back where...

Dear all, I'm going to give a course about black holes at an astrophysics association. The public will consist mainly of lay persons, perhaps wit a little bit of physics background. My background in General Relativity is good, but my background in astrophysics at bit less. My question is if you...

When a Kerr black hole evaporates, what will the Kerr parameter do? Stay constant at initial value? Approach zero? Approach unity? Approach a target value somewhere between zero and unity? Also, Nordström black holes in practice (with matter around) would have a strong tendency to attract...

according to Hawking a black hole slowly evaporates and shrinks (when not feeded from outside with matter falling in). as I understood there comes a moment when it explodes and the singularity disappears. Is this true and if so, how is this triggered? and is there something such as a critical...

Does the twin paradox hold around a black hole (or maybe less extreme gravitational fields)? In a gravitational fields like that of the Earth it seems to apply. If two particles fall together, with synchronized clocks, and one of them rests on a platform for a while, after which it accelerates...

Observational evidence for cosmological coupling of black holes and its implications for an astrophysical source of dark energy Comments?

I was watching a video on GR by mathematician Matt Parker (he of the Parker Square) where he corrected some general misconceptions about GR. Most of the video wasn't anything special but there was one concept that stood out to me: the time-dilato-pause. The idea behind it is quite simple: for...

Hello everyone, I hope I'm asking in the correct section, if not please point me. I read a list of gravitational wave detection. I focused on black hole - black hole events and I noticed the resulting black hole spin is very similar about a=0.7. I didn't find any explanation for this. List of...

(Classical model) The radial "stretching" is caused by differential gravity (tides), but what is the lateral squashing caused by? Is it because the "force" of gravity is not parallel, but instead comes from a point, forming an acute angle? (Einsteinian model) I guess it's pretty trivial to...

I'm really curious about this, but I want to know how wrong I am. I've seen in a lot of content recently about how observations of early supermassive blackholes are observed to be more massive than they should be. If I understand it correctly it has to do with the maximum rate a super massive...

It asked for a snappy title so don’t judge! I’m here for the physics not the BS. And I’ve checked my Dunning-Krugerness & Confirmation Bias at the door! In a way I’ve always been fascinated by physics and the biggest of questions but recently I thought I’d jump in and actually participate as...

I've been seeing popularizations recently that talk as though it's widely accepted that astrophysical black holes contain CTCs. Example: https://www.abc.net.au/news/2023-01-04/are-black-holes-time-machines-yes-but-there-s-a-catch/101822002 Is this accurate? Eternal black hole solutions contain...

You can unconventionally use the Shwarzschild metric to calculate red shift at given stellar distances with some accuracy right out to the edge of the universe. Take the mass of the known universe ~10^55kg. Try it! A bit ironic. I understand this is not how to use the Shwarzchild; however...

In page 67 of book "The mathematical theory of black holes" by S. Chandrasekhar in chapter 2 "Space-Time of sufficient generality" there is a theorem that metric of a 2-dimensional space $$ds^2 = g_{11} (dx^1)^2 + 2g_{12} dx^1 dx^2 + g_{22} (dx^2)^2$$ can be brought to a diagonal form. I would...

I tried solving it and i was able to do a) and b) here is what i did on c), but its not correct according to the solution

I found related questions being debated on the web so i'm not sure wether the question is closed. The following simple reasoning seems to imply that indeed the contracting universe is able to destroy its blackholes but what's wrong with it ?: The black hole solution is usually computed outside...

I've decided my latest novel uses black hole bombs, which aliens create by a mechanism unknown, and which are small enough to quickly evaporate to blast ships in the vicinity. Knowing it is sci-fi and doesn't have to be perfect, about how fast do BHs evaporate? Alternatively, if I need them to...

I am trying to understand how one derives the dilaton monopole interaction. In "Black holes and membranes in higher-dimensional theories with dilaton fields", Gibbons and Maeda mentioned that one could obtain the dilaton monopole interaction as such: where the action is given by However, I...

About a year ago, I heard Leonard Susskind discussing how entangled black holes could create spacetime. As I was listening to Prof. Susskind describe the mechanisms for creating entangled black holes, and how these black holes might create their own spacetime, it occurred to me that if we were...

I have read about the spaghettification of objects due to tidal forces as they get close to the singularity. Gravity at your feet is stronger than at your head, so you get stretched and pulled apart. In this case, the singularity is a point in space. But I also read about the time coordinate...

I will only care about the ##t## and ##x## coordinates so that ##(t, z, x, x_i) \rightarrow (t,x)##. The normal vector is given by, ##n^\mu = g^{\mu\nu} \partial_\nu S ## How do I calculate ##n^\mu## in terms of ##U## given that the surface is written in terms of ##t## and ##x##? Also, after...

What would be the effects of a merger of supermassive black holes? Such releases by far the greatest amount of energy of any event in our Universe as gravitational waves. I suppose that a great deal of EM radiation is released, but I'm more interested in the gravitational waves. The...

IT IS WIDELY KNOWN that from the point of view of a distant, BUT FROM a FINITE distance, the time of falling into a black hole is INFINITE. Then how does the BH absorb the surrounding matter? It turns out that for any observer located at a finite distance R (the coordinate of the Schwarzschild...

I've found highly cited papers that explains inflation with the Higgs as the inflaton and primordial black hole as the dark matter, for examples, These papers solve the inflation with the Higgs and Dark matter with PBH without introducing new particles. Primordial Black Hole production in...

Summary:: The most basic issue queried Why do we know so little about black holes?

If an observer never falls into a black hole, something it observes that does fall in takes an infinite time to reach the event horizon. If an observer falls into a black hole along with an object, it will not lose information on the falling object, but will lose that from the outside of the...