Black hole Definition and 999 Threads

Dark matter passes through everything, but is only influenced by gravity, so in the case of a neutron star, since dark matter doesn't interfere with ordinary matter, it can just pass through it, but neutrinos might be stopped by it's density, as neutrinos can just pass through stars almost as if...

Article: https://www.skyandtelescope.com/astronomy-news/heavyweight-black-hole-find-mystifies-astronomers/

Summary: The Big Band question. Why don’t we live in a black hole? Or do we? That actually might be a stupid question... so don’t hesitate to tell me that. If all mass of our universe was squeezed into something incredible small (compared the universe size) like maybe a tennis ball or maybe...

I read that after explosions supernovas can ”transform” into a neutron start or into a black hole? And now I’m curious of therer any factors which can predict what thing we’re going to get after the supernova’s explosion.

Due to strong gravitational tidal forces, any living observer will die and any macroscopic measuring apparatus will be destroyed before it reaches the black hole singularity at the center of a macroscopic black hole. Hence the black hole singularity cannot be observed, so from an experimental...

If I was looking at a black hole head on (from outside its Schwarzschild radius), would I be able to discern it? Would the stars etc from behind the hole be gravitationally lensed as to "obscure" the hole? Would any of this change when positioned ON, or within, its Schwarzschild radius? Excuse...

As I have studied before, I found that Infinite Red Shift occurs where gtt = 0 but this exercise says that on Kerr's Black Hole it doesn't really work like that. Right now I'm blocked because I didn't find anything on the internet about it so I don't know how to show this phenomenon. Any help...

As a prior physics major (had to stop at my 3rd year of undergrad due to children and financial difficulties), there was something I was always extremely passionate about - finding feasible ways to travel faster than light. Obviously, the only feasible way seems to be to bend space-time, but I...

Summary: If a situation can exist where photons can escape black hole gravity, would “dark star” not be a more adequate name? It is commonly accepted that once there is enough material put together to create a sphere with a mass big enough to prevent light from escaping, that this object then...

For this assume General and Special Relativity and not some of the quantum enhancements that have been proposed for them. If I were an astronaut who just crossed the event horizon on a galaxy center type black hole (big enough so I would not be immediately spaghettified) and avoided the...

If it all started with a big bang of incredible density and energy, does that mean there must be particles that can travel faster than light? How would anything escape the grip of that kind of gravity? I was under the impression that at a certain threshold of mass/density, it turns into a...

According to MIT Technology Review, the Solar System's conjectured 'ninth planet' might be a Black Hole. https://www.technologyreview.com/s/614441/is-planet-9-actually-a-primordial-black-hole/

NASA's website has a video and annotated image of a black hole simulation. It is here. I found the explanations of some aspects of the weirdness of black hole images interesting, but I'm no expert on these things.

From what I understand, a black hole can exist that was formed entirely from antimatter. If this antimatter black hole were to collide or merge with a black hole that has the exact same mass, but was made of regular matter, what would happen? Obviously the matter and antimatter would...

A wormhole collides with a black hole------------what would happen?

Hello! I am a bit confused about the circles of light around a black hole, that were present both in simulations and in that image of a real black hole. I understand that the gravitational field is so strong around the black hole that the light is forced to move in a circular path around (from...

I am trying to derive the radial momentum equation in the equatorial Kerr geometry obtained from the equation $$ (P+\rho)u^\nu u^r_{;\nu}+(g^{r\nu}+u^ru^\nu)P_{,r}=0 \qquad $$. Expressing the first term in the equation as $$ (P+\rho)u^\nu u^r_{;\nu}=(P+\rho)u^r u^r_{;r} $$ I obtained the...

suppose the universe started shrinking. because the density vs mass is a 1/M^2 factor, density can be made arbitrarily small given high enough mass. so it's not hard for all the mass in the universe to quickly reach black hole density. when critical density of the universal is reached, what...

if there's a really good rocket hovering just above a super massive black hole with very low tidal force, and it dips a rod just inside the event horizon, will the rod break? it seems a certainly but the tidal forces are very weak. is it like dipping ur feet into piranha infested water? so when...

How does a Kerr black hole look like from above? Is it the same as a Schwarzschild one? I could not find any convincing visualization for this question. By above I mean from a point r>0 and ϑ=0.

none

In a circular orbit, the 4-velocity is given by (I have already normalized it) $$ u^{\mu} = \left(1-\frac{3M}{r}\right)^{-\frac{1}{2}} (1,0,0,\Omega) $$Now, taking the covariant derivative, the only non vanishing term will be $$ a^{1} = \Gamma^{1}_{00}u^{0}u^{0} + \Gamma^{1}_{33}u^{3}u^{3} $$...

I just wandering about the following hypotetical process to get some information from the inside of a black hole. 1. Drop a satellite into the black hole on a nearly tangential orbit. 2. After it crossed the event horizon drop a large mass after it (for example a small black hole). 3. This mass...

I am new here so apologies in advance. When a virtual particle and anti particle appear at the event horizon of a black hole, before they destroy each other, they are split with one being sucked into the black hole and the other becoming exhaust. Are these the same particles as the quantum...

Hey, If we take a hypothetical black hole with the mass of thirty billion suns which has the schwarzschild radius of roughly the orbit of the venus and let a spaceship fly into it, would it be possible for the spaceship to do some reseach on the physical nature of the singularity and then...

What would happen if a black hole made entirely from anti-matter merges with another black hole made from normal matter? Since most of the product left over from the annihilation is in the form of light (gamma rays) would the black hole lose mass?

Because they evaporate, quantum micro black holes resemble unstable elementary particles: you can create them by smashing stable particles together, and then they will decay back into particles, as if it was all just another scattering process. Certainly in string theory, elementary particles...

It is known theoretical prediction that Black Holes must emit radiation "... its temperature and surface gravity are proportional to its mass divided by its area" (Kip Thorne). This is applied to Event Horizon (rg). But one can imagine inner Black Hole (e.g. inside r' < rg), it does not have...

Summary: Can a black hole merger be approximated as a daughter Schwarzschild black hole created when two parent Schwarzschild black holes pack close enough together to trigger a local Schwarzschild radius containing their combined mass? We know that the radius of the event horizon of a...

Suppose a black hole with a radius equal to the radius of the observable universe exists and a fleet of coasting spacecraft are moving directly away from the black hole (along a similar vector) at very close to the speed of light with an amount of kinetic energy A with respect to the...

I am reading the following paper on the basic physics of a binary black hole merger: https://arxiv.org/ftp/arxiv/papers/1608/1608.01940.pdf Imagine two black holes orbiting each other until a point they merge. As you can see in Figure 1, the wave period is decreasing and thus the frequency...

Suppose there is a 1 million solar mass black hole. A 1.022MeV photon near a nucleus produces an electron-positron pair a distance=A from the event horizon. The positron’s vector is directly “up” away from the singularity. It doesn’t have escape velocity. It reaches an apogee at distance=B from...

In a recent thread we discussed the idea that an object slowly dropped into a black hole, can have its rest mass recovered, as energy, if slowly brought to a halt at the event horizon. Once the object is dropped, it would be unrecoverable, and the BH would gain no new mass. I am under the...

The first law of thermodynamics states that matter can only be transferred from one state to another, and cannot be truly destroyed. What happens to matter consumed by a black hole? What happens to it and where does it go? Does the first law still hold true?

The fundamental building blocks of the universe is thought of super strings, if proved can solve the mysteries of the universe but if proved than how? And how can it solve the mysteries of dark energy &dark matter and black holes?

I was reading another thread which has been closed, so I cannot ask this question there. The question is about a post by @PeterDonis (post #21). https://www.physicsforums.com/threads/what-happens-to-the-inertia-of-a-mass-falling-into-a-black-hole.970627/ There are no internal pressures inside a...

I am wondering if an object can fall into a black hole at faster that the speed of light. I have heard that the expansion of the universe can make distant galaxies appear to recede from one another at velocities faster than the speed of light.

 Intuitively, this makes sense to me. I am...

I just watched a youtube video saying that somewhere in a black hole, time is bidirectional (can go to the future and can go to the passed), but space is one-directional. Any introduction material on this subject? Thanks in advance!

Do all black holes have the same gravitational pull yes or no, and if not, is it possible that if space and time bends on itself and connects two black holes that the one with the strongest pull will continue as a black hole and the weakest will turn into a white hole considering the amount of...

What happens to the inertia of a mass falling into a black hole? I am not even sure if I frame the questions correctly. Will this mass reach the center or is mass distributed within the black hole? Is the singularity the whole volume of the black hole or is it a point in the center? If a large...

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...