Black hole Definition and 999 Threads

I'm sure this has been asked before, but it's lost to me among all the false positives... If falling into a black hole would lead to you being spaghettified, and moving relativistically towards it would contract your length / etc., is there a speed at which they balance out? Seems calculable but...

From Randall Munroe (http://xkcd.com). It left me speechless.

Suppose a black hole isn't sucking in any new material. Then it is doomed to evaporate due to Hawking radiation and become smaller and smaller over time. Is there anything left when it's done evaporating?

We all heard about the "photo of black hole". My question is: did this image show any hints of physics beyond general relativity? I read once (not sure where) that the apparent size of black hole shadow is very sensitive to corrections to general relativity. Add some minor correction and the...

I'm a physics student and science fiction writer, and I've never been to this section of PF before! But I have an idea I think is cool for a novel or short story and I'd like some input on the physics involved. As I'm not overly worried about this idea being stolen I'm going to provide a short...

I was wondering recently what a black hole's tug/pull/ sucking effect would feel like if you could stand on a planet at a totally 'safe' distance, for example, or fly by perpendicularly. I came up with 2.5 trillion miles or .43 light years, give or take. I compared the diameter of the sun...

M87 Black Hole Photos and the Orientations the Angular Momentum of the Black Hole and that of the Accretion Disk. I’m trying to understand the orientations the angular momentum (let’s call it spin) of the black hole and that of the accretion disk. Veritasium has good video on the topic [1], but...

Curious if the ongoing studies of black holes at the centers of galaxies, like the Event Horizon Telescope, might provide some clues about the nature of dark matter. Tried googling this, but all I get is articles debating, mostly to the negative, the hypothesis that dark matter might be...

I know that has been discussed elsewhere but never could find for a satisfying answer, so I try this here again. Let us not take into account that an observer (an astronaut or a clock or just let us take both: an astronaut with a clock) falling into a black hole (BH) will be killed and torn...

I do not know if this image is a true image but for scientists to see a black hole is some thing. https://www.sciencedaily.com/releases/2019/04/190410091028.htm

It would seem that they both must observe the laws of General Relativity.

Lobes Did anyone hear an explanation of the appearance of the lobes visible in the published image? I only caught part of the Q&A. (Visible most prominently at at eleven o'clock and four o'clock positions, and to lesser degree at three and nine) Do these type of observations generate "lense...

This week, leading up to the release of the pictures of the super massive black hole Sagittarius A* at the center of the milkyway, I have done a bit of background research on the topic and learn that they are also looking at trying to get an picture of the super massive black hole at the center...

Hello! Dark Matter (if exists)(if it is in form of particles - collisionless) could also be attracted by Black Holes (or Neutron Stars) and form accretion disk. I would like to discuss possible properties of such hypothetical object. DM particles could be trapped and settled in around...

I am reading the paper https://arxiv.org/pdf/0801.4591.pdf , says "Fortunately, the fact that the heat capacity of the cosmological horizon be positive permits to foresee the evolution of the space in absence of any external source. Taking the correct signs for the temperatures one can notice...

Dear all, I have a question on Penrose diagrams. Consider a collapsing star that forms a black hole with a Schwarzschild radius normalized to 1. What happens in the Penrose diagram when additional matter falls in? I suspect the diagram then has to look like this : When the outer shell (second...

What are some of the challenges associated with calculating orbital parameters of objects around a black hole (I.e. Orbital velocity, period, semi major axis, kinetic energy). At what point can classical physics no longer provide accurate results?

I thought I'd create a new thread rather than derail. In https://www.physicsforums.com/threads/if-quark-stars-exist-why-do-neutron-stars-become-black-holes.937452/#post-6143231 it was explained to me that gravitational waves do not escape the interior. The reason I thought they did is that we...

I would like to know, how much a stars life would appear to lengthen relativisticly as observed from earth, if the star was in a close orbit around a supermasive black hole. If the stars lifespan is longer from our perspective than a star of its size should be, would it also appear to be...

Here we consider a black hole formed by gravitational collapse classically. We also consider a scalar massless Klein-Gordon field propagating on this background. To quantize the field we expand it in appropriate modes. The three sets of modes required are: The incoming modes, appropriate for...

Scenario: You have two black holes approaching, one from the left (A), one from the right (B), each at speed S. They are offset vertically. S is sufficiently high that they will deflect passed each other without merging. Question: Suppose the speed S is high enough so that the event...

What happens to matter after it falls into a black hole? Are electrons pushed closer to the nucleus? Do electrons combine with protons to form neutrons? Are there nuclear reactions occurring in the process? Since no light can escape from a black hole and cool it, then how can a black hole...

I came across a question on PSE. I am not sure its a violation to ask the same question here, but there's no answer to the question in there so I wanted to ask it here. Quoting his question,"Since the universe has a positive cosmological constant, there is an upper limit on the mass of the...

I am under the impression, there is no unique solutions to Einstein's field equations for a cosmological constant, or for higher dimensional spacetimes. Has anybody got a counter example for a solution including the cosmo constant to show there are multiple solutions, for example, i know of the...

I am working on a research project where I intend to describe what the Penrose process would like in a sonic black hole. I have found what a rotating (Kerr) black hole looks like in the sonic analog: https://arxiv.org/pdf/1802.08306.pdf I have also found that the analog of massless particles...

Whether it be through Hawking radiation, miniature black holes, or even white holes, is it possible that one day energy could be harnessed from black holes and used on earth?

I'm trying to visualize what a fast spinning supermassive black hole slowly eating a stellar black hole should "look" like; how would the mass flow between the two? Could enough mass be removed from the stellar black hole, that it loses it's event horizon before entering the supermassive black...

It is stated that a Black hole has only mass, angular momentum and charge for properties, but since it is black ie no light escapes its event horizon and charge E/M is related (same speed) as light (photons), how can unbalanced charge be detected? And since many Black holes have electron...

Dr James Farnes of Oxford's e-Research Centre recently proposed a new model which unifies dark energy and dark matter into a single phenomenon - a fluid which possesses "negative mass". https://news.sky.com/story/mystery-of-dark-matter-may-have-been-solved-by-oxford-scientists-11572089 The paper...

When we approach a black hole, the effect of gravity is such that relative to us, time far from the black hole would approach infinity as the distance to the Event Horizon approaches zero. But what happens when we cross the Horizon? How do we measure time outside? Will infinite time have have...

Hello everyone, By considering the effects of the gravitational time dilation the speed of the inner stars must be higher for the local observer than for the external one. So why the gravitational time dilation can not potentially explain the galaxy rotation curve? I already read that the...

This paper by Christodolou and Rovelli discusses how to define the interior volume of a black hole: https://arxiv.org/abs/1411.2854 I'll try to condense their basic argument into a (heuristic) form that makes it easier to raise the issues I want to raise. The basic idea is to start with the...

I read that 1. dark matter has to be concentrated in galaxies; 2. McGaugh & Co discovered a precise relationship between visible-ordinary matter and the calculated sum of ordinary + dark matter from thorough observation of actual acceleration of more than 150 galaxies. 3. First experiments to...

Hi Everyone, I'm interested in how to annihilate black holes (they are like blenders separating all the things apart and agglomerate like "tumors/cancers" in the universe). However, I'm new to this field and need some clarifications on some of the basic concepts like "annihilation" and...

So I'm trying to help someone get an idea of the 'scale' of some of the most massive black holes, but, I'm at best a laymen when it comes to this stuff. Because ISCO for a non-rotating black hole is just 3 times it's radius, and I can calculate apparent arc radius from ISCO, I could tell them...

I am working on a presentation for a course in general relativity and my topic is the stability of black holes. In many of the references and articles that I have found, the author asserts the importance of the conjecture but offers no reason. So I ask: Why is the black hole stability conjecture...

Just a question: Can anybody give any information regarding the black hole paradox? There are so many theories behind it. Which one should we believe? Just a general question.

So, if the Earth moves slowly through a large hula hoop, sensors attached on the hoop will measure some stresses, which we might call tidal forces. The faster the Earth moves relative to the hoop the larger those tidal forces are. So, if a person falls into a black hole, there are some tidal...

In the way I naively imagine a black hole's interior there are event horizons all the way down, and any material object of whatever size will straddle many event horizons. So, with both atoms and baryons, there cannot be any interaction between their components. Consequently, at the moment of...

let's imagine that we can create a black hole from dark matter. Is it going to be different from the ordinary black hole(which is created by ordinery matter)?

Hi, I'm new on here and this is my first post, so forgive me if I don't master the threads instantly :) - right, now that's out of way: I want to open a discussion on the singularity in Black Holes, namely in regards to the well known issue of Special Realitivity breaking down at the...

Are a Schwarzschild singularity and a black hole the same thing?

Hello people, I have been thinking about a concept that I was taught whilst learning GR, If I understand correctly it is that Lorentz symmetry becomes local when we consider GR. This makes sense to me as then the metric is generally speaking not Minkowski, only for a...

Do black holes accumulate neutrinos ? Do the neutrinos that fall in, decay in some way , maybe interact with the condensed matter, or just stay "parked" in perpetual loops ?

Is entropy consistent from all reference frames? For an observer at the surface of a black hole, a finite amount of time would pass, but the observer would observe an unbounded amount of time passing for the outside universe, hence from his/her reference frame, information, entropy of the...

Conformal Cyclic Cosmology, or CCC, is a hypothesis put forward by Roger Penrose in the early 2000s. My understanding of physics is lacking so my explanation will not be that clear, but I will summarize it here. Essentially, the existence of a previous spacetime, or "aeon," is postulated. This...

The Wikipedia entry on "White dwarf" has a table listing the densities (in kg/m3) of various objects/substances, and states that an earth-mass black hole has a critical density of 2 x 1030, about 13 orders of magnitude denser than atomic nuclei. Has such an enormous density been calculated...