Black holes Definition and 1000 Threads

Does dark matter(DM) fall into black holes(BHs)? IMHO it should... ...as it does interact with normal matter gravitationally. Once it's done so, does it add to the BH's mass? Again, IMHO it should. AFAIK it does have mass... Would that "quasi-convert" it to normal matter? ...after all, this...

Homework Statement:: See below. Relevant Equations:: See below. I am trying to calculate the event horizon and ergosphere of the Kerr metric. However, I could not seem to find a proper derivation or formula to calculate the event horizon and ergosphere. Could someone point me to the...

I know some basic GR and encountered the Schwarzschild metric as well as the Riemann tensor. It is known that for maximally symmetric spaces there is a corresponding Riemann tensor and thus Ricci scalar. Question. How do you calculate the Ricci scalar ##R## and cosmological constant ##\Lambda##...

I am just wondering if placing the Earth equidistant from 3 black holes that are spinnng would slow down time on the Earth, due to the time dilation effect. Would that give us more time to live?

I'm pretty sure I know the responses I'm going to get, as this question is pretty silly, but I'll ask anyway. Is there anything - a process, or a material, that would reduce the size of a black hole and/or evaporate it away quickly, or is that just hocus pocus thinking?

Let's say you have two extremal black holes containing the maximum amount of possible charge. Now let's say they're orbiting each other such that they will eventually merge. As the black holes merge they are producing gravitational waves. Once the merger is complete the new black hole mass will...

In Chandrasekhar's book, The Mathematical Theory of Black Holes. The sign of Einstein equations is minus "-" , Eq. (1-236). However, the sign of Riemann and Ricci tensor are the same as MTW's book. The sign of Einstein equations in MTW's book are "+"! Is there a error?

A popular theory is that black holes gradually leak information because of black hole evaporation due to hawking radiation. When black holes merge, a significant portion of their mass is converted into gravitational waves. If it's true that black holes leak information due to hawking radiation...

I keep seeing this figure of 3-4 Solar masses is all that's required for a star to end its life by collapsing into a black hole. Since the sun is a pretty average star, that would suggest that most of the stars in the universe (like >50%) will end their lives as a black hole. The implication...

Are there any papers or articles that reference black holes being the creations of the big bang or being considered in creating universes in alternate dimensions? Thanks for the help.

Could dark matter consist of black holes formed shortly after the big bang? They would form the perfect development seed. If they all have Sun-like masses then they are not detectable from here (they are just 3 kilometers wide!). They have virtually no collisions with stars and could form a...

When a photon travels through space it is spreading out like a fan while in its superposition (except that it is spreading also vertically in addition to horizontally). So, what happens if for instance the right outer edge of the photon's superposition is captured by the gravity of a black hole...

Would it possible that black holes share a quantum entanglement with stars(such as white dwarfs), and the reason we observe the tunnel closing is the star dies out/explodes? I understand that there are different types of black holes and stars, varying in size and properties of mass/spacial...

From "standard" formula we have that the gravity acceleration a = GM/r^2 and that the Schwarzschild radius rs = 2 GM / c^2 Is it possible to compute the gravity acceleration at Schwarzschild radius putting r = rs? In this case we will have a = c^4 / (4GM) This mean that a very very...

Does black holes determines time's arrow? Otherwise how to explain with time reversed objects been pushed out from black holes?

So I am a fan of astronomy, cosmology and astrophysics from a FAR. The math is way beyond my abilities but I like to just sometimes read and think about the very small parts I am able to comprehend. So my hats off to all of you that are able to fully enjoy this stuff, you're very lucky...

As closer the observer will be to the event horizon, the more the time dilatation will be. As we know, if the observer O1 has a clock, another observer O2 very far from the black hole will se the O1 clock "slowing" down as O1 approach the event horizon. The limit is that the O1 clock "stops" at...

Just saw a documentary about resolving Hawking's "information paradox". In my own lay terms the physicists appear to theorize resolving the paradox with with their proposed C = 12 J . C is the central charge (which I don't fully understand) and J is the total angular momentum of the black...

So recently I watched a video detailing how it is impossible to measure the speed of light in a straight line because it's not possible to synchronize two-time measuring devices without first knowing the speed of light. But I was thinking if light can orbit a black hole in the photon sphere...

Hello everyone, im new in the forum and this is actually my first post. I am not an expert of astrophysics but for sure a very curious person that hope to can get more knowledge about astronomy and physics in the next future. Its been kinda long time I am searching an answer to some questions...

hey Im new here, I am a masters degree student. I woud ask about any good source for understanding black hole for a master's degree student. thanks

The Onion tackles black holes. https://www.theonion.com/step-by-step-how-do-black-holes-work-1846628568

If you search on-line for "efficiency of a black hole" you will get several discussions suggesting that the efficiencies of converting mass to energy are from 6% for non-rotating black holes to 42% for the fastest rotating black holes. I would like to know exactly how black holes convert some of...

A new pre-print makes a sensible and convincing, in my view, argument that phenomena attributed to dark matter are not exclusively or predominantly explained by primordial black holes formed at less than the mass of a star shortly after the Big Bang, by means other than stellar collapse. This...

Hi, I'm a Portuguese translator working on a documentary about black holes and there is a specific bit of dialogue between Stephen Hawking and his colleagues that I'm having a hard time translating. Basically, Hawking says: "So, it could be the F plus minus term takes this away." Is this the...

If dark energy causes spacetime or things in the galaxy to expand (acceleratingly), then won't black holes die due to expansion past the Schwarzschild radius, rather than simple radiation evaporation? (When black hole die, I mean, we have the ability to look into the space because it is no...

How did you find PF?: duckduckGo search. My math is very weak and I don't like explanations done using math. I read books with very little math. I try to use reason based on what I've read. My understanding is time slows down in gravity and it will actually stop at the event horizon (see...

I want to ask if you can theoretically chill the particles of a black hole and if it is possible to achieve it what will happen

My hypothesis: A sequence with the gravitational waves detected, sent by modulating radio waves, could be received and used by other intelligent beings to find the corresponding sequence within their records and then compare it to calculate our spacetime position in relation to theirs. As...

My understanding from General Relativity is that if as distant observers we watch a probe or any test mass approach a black hole, time dilation goes to infinity as the probe gets closer to the event horizon. This would imply that we would never observe a black hole form, or the collision of two...

I am currently studying the Vaidya metrics and I am a bit confused regarding the term Misner Sharp mass, and I am referring to Blau notes and in them the description is very deep which I surely don't need but just an overview. TIA

The reason why I think it could happen is that spacetime is being curved really extremely in black holes and when you draw a chart of spacetime near and in black hole , you can see that time axis is being bend towards the center of black hole and that thing is happening from all sides of the...

Before explicitly stating the Kerr metric let us discuss a bit what to expect, comparing it to the easiest solution to (in-vacuum) Einstein's equations that I know: the Schwarzschild metric. I studied that the Schwarzschild metric is derived under the following assumptions: the metric must be...

Well, my question arises because when one hears about black and white holes in divulgation, usually one hears that they are two kinds of "objects", the first one is a region that can only absorb things, and nothing can escape from it. While the latter is a region that only emits things and...

Does Hawking radiation at the event horizon of a black hole result in the reduction of the mass of the black hole? Quantum mechanics requires the creation and destruction of particle-antiparticle pairs throughout space-time. When this effect occurs at the event horizon of a black hole...

Do black holes exist? I have largely only heard that mathematically physics rules break down inside of a black hole by its current definition and that nothing can escape it beyond a point. And Hawking radiation has already shown to escape it beyond an event horizon. And Stephen Hawking in 2014...

For the Black Hole Bomb to be effective, does it need the mirrors there, or can they be replaced with wormholes, or some other quirk of spacetime?

I just want to know if Black Holes would be quantumly coherent.

My fascination with black holes runs very deep. I was wondering if anyone could shed some light on two questions I have: Do black holes orbit around another object, or are they "free-roaming"? If they do, what determines which object they rotate around? The place where they form, or some other...

How does mass determine the bending of space from inside a black hole?REPLY

Hello, This is a question I've been pondering on my own for some time. I have no formal education in advanced physics, only at the introductory undergrad level. I read that immense pressure can create black holes by compressing matter. I've read Laurence Krauss explain you'd need to compress...

A Paradox of the black hole is that GR states the stationary observer experiences time dilation, while the inflating observer experiences no time dilation. By the time the infalling observer reaches the event horizon, an infinite amount of time passes for the other frame of reference. But...

The paper is reasonably old and was written as a phd thesis by (I believe) a man from china. It was basically the first paper on the subject and in it he effectively (from what I understand) dropped particles into a black hole, counting the information added, and saw that the black hole changed...

Hi everyone, been reading this site for a while, and this question has been stuck in my head for 3 days and i can't shake it, so i figured I'd step out of the shadows and ask. There are some follow up questions that came on the same train of thought too. Can light pass by a Black Hole and get...

This should maybe go in the Beyond The Standard Model forum but since it's a paper about quantum cosmology I'll put it here. Feel free to move it if it's too speculative but that's exactly my question. That is: if it is... Perusing "The Area of a Rough Black Hole" - -...

Three Lectures on Complexity and Black Holes - could be a good read for quarantine!

I am grateful for anyone for their time to answer this question. Some theories predict black holes will evaporate and eventually disappear. From my limited understanding, Hawking's theory predicts that quantum effects near the event horizon of a black hole are responsible for blackbody...

This is on page 2, and I guess it is the key to understanding what they mean by linearized perturbation to a BH in the abstract. What is meant by gravitational fields, what is delta(g_ab) and delta\Phi ? A perturbation to the metric, and the 'gravitational field', sure. And where are these...

Physically speaking, why the insides of the least massive black hole should be any different from the heaviest possible neutron star?

After binge watching Steins;Gate, it has had me thinking about black holes. In the show it mentioned the idea of microscopic black holes(CERN). That being said, if matter and energy have an "equivalence", and if the Schwarzschild radius depends on mass, then would it be possible to confine a...