What is Black hole: Definition and 1000 Discussions
A black hole is a region of spacetime where gravity is so strong that nothing—no particles or even electromagnetic radiation such as light—can escape from it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. Although it has an enormous effect on the fate and circumstances of an object crossing it, according to general relativity it has no locally detectable features. In many ways, a black hole acts like an ideal black body, as it reflects no light. Moreover, quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation, with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is on the order of billionths of a kelvin for black holes of stellar mass, making it essentially impossible to observe directly.
Objects whose gravitational fields are too strong for light to escape were first considered in the 18th century by John Michell and Pierre-Simon Laplace. The first modern solution of general relativity that would characterize a black hole was found by Karl Schwarzschild in 1916, and its interpretation as a region of space from which nothing can escape was first published by David Finkelstein in 1958. Black holes were long considered a mathematical curiosity; it was not until the 1960s that theoretical work showed they were a generic prediction of general relativity. The discovery of neutron stars by Jocelyn Bell Burnell in 1967 sparked interest in gravitationally collapsed compact objects as a possible astrophysical reality. The first black hole known as such was Cygnus X-1, identified by several researchers independently in 1971.Black holes of stellar mass form when very massive stars collapse at the end of their life cycle. After a black hole has formed, it can continue to grow by absorbing mass from its surroundings. By absorbing other stars and merging with other black holes, supermassive black holes of millions of solar masses (M☉) may form. There is consensus that supermassive black holes exist in the centers of most galaxies.
The presence of a black hole can be inferred through its interaction with other matter and with electromagnetic radiation such as visible light. Matter that falls onto a black hole can form an external accretion disk heated by friction, forming quasars, some of the brightest objects in the universe. Stars passing too close to a supermassive black hole can be shred into streamers that shine very brightly before being "swallowed." If there are other stars orbiting a black hole, their orbits can be used to determine the black hole's mass and location. Such observations can be used to exclude possible alternatives such as neutron stars. In this way, astronomers have identified numerous stellar black hole candidates in binary systems, and established that the radio source known as Sagittarius A*, at the core of the Milky Way galaxy, contains a supermassive black hole of about 4.3 million solar masses.
On 11 February 2016, the LIGO Scientific Collaboration and the Virgo collaboration announced the first direct detection of gravitational waves, which also represented the first observation of a black hole merger. As of December 2018, eleven gravitational wave events have been observed that originated from ten merging black holes (along with one binary neutron star merger). On 10 April 2019, the first direct image of a black hole and its vicinity was published, following observations made by the Event Horizon Telescope (EHT) in 2017 of the supermassive black hole in Messier 87's galactic centre. In March 2021, the EHT Collaboration presented, for the first time, a polarized-based image of the black hole which may help better reveal the forces giving rise to quasars.
As of 2021, the nearest known body thought to be a black hole is around 1500 light-years away (see List of nearest black holes). Though only a couple dozen black holes have been found so far in the Milky Way, there are thought to be hundreds of millions, most of which are solitary and do not cause emission of radiation, so would only be detectable by gravitational lensing.
[Reposted from my PF Blog.]
I haven't yet had the pleasure of participating in a PF thread on this topic :wink:, although I have made at least one post that refers to it in passing. But I know there have been some in the past, such as this, so I wanted to post a quick treatment of the topic...
Black holes are usually shown as funnels. Is there one "funnel" pointing in a single direction or are there event horizons and "funnels" seen from every direction?
Hey! I'm new here and I just wanted to ask a question and maybe I'll come back here once I have started college in a week or so. :P But firstly I must say, at first I thought the confirmation question for signing up was a science question about acid and I was totally stumped. But that's PH... I...
An interesting article for ordinary people but I just wondered if it is science or pseudo science?
It offers an explanation why the Universe has a beginning and has finite age.
To me it suggests many Universes occurring at random, like raindrops falling randomly into an ocean of space time...
Thinking about how so much matter can be squeezed into a singularity, the answer (if I understand correctly) is that the matter just stacks upon itself down an infinitely long weird space-time well. In a sense, the last item in masks the ones below.
But doesn't this impact the gravitational...
Experiment:
Imagine the dalayed time quantum eraser experiment, except the pair of "idler" photons(which would normally pass onto the detectors d1,d2,d3,d4) instead fall into a black hole.
Would d0 detect interference or not?
It seems commonly accepted that the information of...
Are there any EXACT solutions similar to Schwarzschild or Kerr in a spacetime which is not asymptotically flat; e.g. FLRW or other cosmological metrics? I am already familiar with the "Swiss cheese" approximations.
Hello. I'm a layperson curious about physics.
I've read that Quantum Gravity could eliminate the predicted singularity inside a black hole based on General Relativity.
If that's true, what would happen from the frame of reference at the center of a black hole? Would that cause a tremendous...
Consider two black holes: the left one has a mass M1= 5x10^30 kg, and the right one has a mass of M2= 9x10^30 kg, and they are a distance d= 3.0x10^6 m apart. A spaceship passing between them is having engine trouble and so the captain has to park the ship somewhere where he won't get sucked...
Please excuse me for being a complete and utter pleb, my meager knowledge of Leonard Susskind's holographic principle comes from the second episode of the documentary "Through the Wormhole" (which is available online but I won't link to in case it is copyright infringement?).
He talks about...
Let's imagine a stationary black hole and a fast moving object falling into BH. Let the momentum of the falling object be enough to give an observable bump to BH, pushing it into motion.
Since the object does fall into BH, by momentum preservation BH should start moving. But I don't see how...
What are the equations that shows that time slows down as you near a black hole? I'm trying to prove to a non-believer that the math is there and shows this. Thanks!
http://arxiv.org/abs/1407.0989
White hole anyone?..^^
"...intense gravity creates a horizon, but it is not an event horizon. It is locally like an horizon, but not globally. So, matter is trapped for a while, but not forever; it is called sometimes a “trapping” horizon."-CR
Instead of being a force that works against gravity. Is it possible that dark energy is the pulling of everything towards the event horizon of a black hole? This would marry dark energy with gravity and replace myserious massive amount of energy with a logical source of energy/force that we know...
So as I understand it, Hawking theorized that due to the behaviour of virtual particles on the event horizon of a black hole, eventually the black hole would "evaporate" through what was coined the Hawking Radiation. But what I'm curious about is Hawking's interpretation of the event in that...
By theoretical calculations of super dense black holes show their gravity exceeding to a limit that can pull in light into the heavenly body. This means that the gravitational pull, which are actually acceleration as shown by the Relativity theory, is greater than the speed of light. So won't a...
Hi!
New here. Be gentle.
Kinda an idea that popped into my head a little while ago:
Are the tidal forces of some black holes powerful enough to separate quark groups? Google seems to be a bit iffy on the subject.
It is confirmed that Black Holes have variations of masses. But these masses are said to be gained from the base mass from the Supernova it's born from. Another way a Black hole gained mass was that the collisions of multiple Black Holes caused it to add on to the mass of each other, such as...
Was thinking about this why is it a requirement that the center of a black hole be a singularity? If the event horizon contained all the mass of a black hole would it still not have the same effect on it's surroundings? Why could it not be similar to a a crystal where as each molecular link or...
So, I lay a rope into a black hole, rope leaves the reel at velocity 0.99 c.
When I observe the lower end of the rope, I never see it reaching the event horizon.
Can I see some slack rope somewhere sometime?
Hi, I am not too sure where to post this. I am studying for my astrophysics final and I came across this question which is pretty easy ( I think) but I can't seem to find the answer...
S2 is observed to be one of the brightest stars orbiting the black hole at the center of Milky Way. It has...
So I have a question about Sagittarius A*, which more and more astrophysicists are certain is a supermassive Black Hole. But now for the evidence part:
1. An alternative model for this object was proposed http://journalofcosmology.com/RobetsonLeiter.pdf published 4 years ago. So is there any...
(Correct me if you think I'm wrong in anyway, I am open to new ideas.) A black hole is created when a planetary mass has its atoms completely cave in on its self. This creates a massive amount of gravity, one so massive that it even attracts photons (light). So does this mean that a black hole...
Hello, if you could help, I will be glad.
I am studying the Einsteins-Rosen bridge (a matematically solution of the black hole) and I thought that the Einsteins-Rosen bridge was what we found making the Schwarzschild metric a change in kruskal coordinates. But reading an scientific article it...
Suppose a black hole travels at something like v = 0.999999999c relative to some observer. Does the black hole's event horizon becomes length contracted, thus appearing to turn into a black disk?
Hello,
I am interested in surface gravity of Kerr black hole it means, I need to find killing vector for Kerr which is null on outer horizont. Is it true? How should I do that? I guess it could be some linear combination of vecotrs ∂/∂t and ∂/∂\phi. So can I looking for that this way...
Here is my basic question:
Lets say we have a massless charged shell with charge q and radius R. Is there some R where a black hole is formed?
I haven't work this out with the EFE, but the calculations I've done are relativistic (GEM equations instead of EFE, for simplicity). I found that...
I have a question pertaining to objects falling through the event horizon of a black hole.
It is my understanding that due to the immence gravity of a black hole and the way gravity affects the flow of time, that from the point of view of an observer at a safe distance from a black hole...
Lets say we have a couple objects, one very close to a black hole, one a little farther out and then one a good distance away. Would the one very close to the black hole see the other ones time moving much quicker than their own time? How about just as they are going to hit the event horizon...
Requested info for a sci-fi short story I'm writing:
You are approaching the event horizon of a supermassive (10 billion Solar masses) Schwartzchild black hole in a magical spaceship which is capable of violating the laws of physics. You have not been free falling but lowering into the hole...
Hi, I've heard and read that if someone was to fall towards a black hole, say feet first, they would undergo spaghettification at a certain distance, as the gravity at their feet would be much greater than the gravity at their head, and their body wouldn't be able to reisist the pulling effect...
Imagine a spinning skater. She pulls her arms in a little and spins faster. She brings her arms all the way into her chest, and spins really fast, and then bam! she rockets up into the sky. Seven years ago, computer simulations revealed a configuration of two spinning black holes that merged in...
I think I am wrong in what I am about to say so I someone could explain relatively simply where I went wrong I would be thankful...
When light travels towards a black hole it's wavelength increases it's frequency and decreases it's wavelength due to the increase in energy. Because a black hole...
The FAQ states:
"In our universe, we observe that space is not a vacuum, and tidal forces are nearly zero on cosmological distance scales (because the universe is homogeneous on these scales). "
We observe Dark Energy. How do we know this accelerated recession of distant galaxies, which is...
First off I couldn't decide whether to enter my question in the relativity section or this one, so if I'm in the wrong place my apologies. Anyway I have a question or perhaps a hole in my understanding. I was wondering if there is a density point at which anything becomes a black hole. Now I...
Hi,
does anyone know how much of the universes's iron or carbon has been made in supernovae that formed black holes? Is it 5, 10, 50 % of the iron currently pressent here?
And, if se, do we have any idea how much of the average stars content gets traped in the BH versus the mass of the...
Hi,
I think I have several misconceptions about the theoretical framework of black holes, I'm just not sure where my intuition (or, lack of) goes wrong. So sorry if this sounds really stupid, any help is appreciated.
The scenario that I find confusing is what Alice sees when she throws Bob into...
I was thinking about how a black hole evaporates and the firewall idea. If after Page time a firewall forms around the black hole, does that mean that the energy/mass, and entropy cannot increase anymore? The energy of the black hole is essentially supposed to be in the singularity, right? I...
I thought this was cool, wasn't able to find a paper on it, but didn't look "super hard", and won't pay for it.
Apparently, a gravitational lensing has lined up so perfectly that we were able to measure the black hole's spin. They have it at "half the speed of light" (??!)...
Assume that there exist two people, person A and person B. Person B is falling into a black hole.
I understand that due to relativity and time dilation, person A will have to spend an infinite amount of time to watch person B cross the event horizon. Person B will appear to move at a slower...
I know several raytraycing results for static Schwarzschild black holes, but I have never seen something similar for collapse models like Oppenheimer-Snyder or Vaidya.
Are there reliable raytraycing results showing the effect on light rays from far distant light emitters observed by (far...
In a Kerr Black Hole there exists a region called the Ergosphere.
It is between the Event Horizon and a spheriod called the Static Limit.
The Event Horizon can be simplified to: ##\Delta## = 0.
The Static Limit can be simplified to: ##g_{tt}## = 0.
They yield two separate spheres...
Homework Statement
How do you find the Angular Momentum, J, if you are given the Angular Velocity, ω of a Kerr Black Hole.
Homework Equations
J = I*ω
##I = mass*r^2##
Event Horizon:
##r_+ = M + (M^2 − (J/mass/c)^2)^{1/2}##
Static Limit and the Ergosphere:
##r_0 = M + (M^2 −...
Suppose Alcubierre warp drives or some alternative form of warp drive is possible. Then surely a warp drive could enter the event horizon of a black hole, observe the interior, and exit the horizon, returning with information from within the black hole. What about black holes never visited by a...
In another thread we determined that the proper total force acting on an orbiting object in the Schwarzschild metric, is given by:
##f_{total} = \frac{Mm}{r^2\sqrt{1-2M/r}} - \frac{mv^2}{r}\left(\frac{1-3M/r}{(1 - v^2)\sqrt{1-M/r}}\right)##
One interesting aspect of the equation is that when...
If light approaches a black hole will it accelerate? I think this question ties in with whether light has mass or not. Does light have mass? It seems accepted that light has momentum, but this is not consistent with saying that photons are mass-less (momentum=mass*volume). Could someone clear...
Hey all,
I was wondering if the singularity at the bottom of a black hole is similar to what the universe would be like before the big bang, i.e. heaps of mass/energy concentrated into a tiny point.
To me I always think of black holes as sinkholes dotted throughout the universe which are...