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.
I am confused about black hole horizons and such common statements as "light cannot escape from inside the horizon".
The way I currently understand it is as follows :
1. Horizons are always relative to an observer, and what is called "the black hole horizon" is just a shorthand for "the black...
As multiple stars would collapse into a black hole, are the electrons shot outwards? Or are they converted into mass with infinite density (what a black hole is right?)
Thanks.
How close do you have to be from a black hole to experience noticeable time dilation. I always believed you will not experience noticeable dilation until you are at or in the event horizon is this correct?
Also does rotation/spin of mass such as a planet decrease it's inherent gravitational...
Rovelli & Vidotto's Planck Stars describes a possible quantum black hole - white hole transition through a quantum bounce somewhat analogous to the LQC bounce.
In another thread, @marcus pointed out to me that this was not necessarilly considered the most likely scenario for a QG black hole.
Is...
What would happen if there was a supernova explosion near a black hole ? Would it just sit there and absorb all the energy incident on it ? Or would it simply vaporize into elementary particles ? And if it does vaporize, could the remnants give us a clue as to the quantum state of matter inside...
Black holes grow by absorbing matter, which includes galaxies and black holes. Would the growth of black holes overtake the expansion of space time and collapse the entire universe?
So I was reading threads and i came across a question on what happens when a black hole collapses. As I was reading the responses, I saw some people commenting in which they asked if the mass the black hole absorbed was released when the black hole collapsed. If it did would the black hole...
What do you put inside einstein field equation for black holes? Why is it that such black hole solution is not feasible?
Isnt the schwarzschild metric a solution for black holes? How is it not feasible?
I know that black hole have strong absorb force even light can't escape,so if we get near i think we can't also escape,but i want to know what will happen when we reach inside the black hole? and what happen if two black holes meets,what will happen if it come near to earth?
I'm curious about what others think. As I believe that you fall indefinitely in a black hole, and since you don't feel the gravity when falling, you fall until your incinerated by faster moving electromagnetic radiation falling on you. But you can only see what is above you, assuming your eyes...
Is there a physical boundary that is the event horizon? Or is there not?
The reason I'm asking is because texts say that the event horizon that appears in Schwarzschild's metric is a result of the coordinate choice, and it disappears by choosing some other coordinates.
(I don't know if this is the best place to ask this, if not please feel free to move it elsewhere or delete it.)
A number of Quantum Gravity papers explore the evolution of Black Holes and their potential transition to White Holes, and some discuss the possibility of astronomical observation of...
I thought that this might be a concern for the standard Cosmological model?
An extremely large Black Hole discovered to have existed just 900M years after the Big Bang...
If the Singularity Has Infinite Mass, How Does Merging With Another Black Hole Create "Suoermassive" Black Holes? Infinite Plus Infinite Is Infinite. No Increase.
I am fifteen and I attend High Tech High International and I have to teach a hour long lesson on Black Hole Buoyancy. And I was wondering how to do that. Can I have some suggestions or help?
Hi there,
I was reading one of my textbooks and I had a thought. For a black hole, there is minimum orbiting radius of ##R_{min}=3R_s## where ##R_s## is the Schwarzschild Radius. This minimum orbit is created by the fact that in order to obtain an orbit of that radius around a black hole, you...
How exactly did Hawking compute that black hole entropy is 1/4 that of a Planck area and concluded about the holographic principle where information of a volume is located on the area of black hole? And if there was no holographic principle, how big should entropy of the black hole be with...
Hello :)
I had a question , i recently red a lot about black holes and i had a question about the Schwarzschild
Radius . How does that come that π is not in the equation ? The black hole is a sphere so instinctly one could think that Pi should be in the equations.. ?
P.S: I'm french and 16 so...
Hello. I'm thinking about Hawking radation and there's one thing I find a bit strange. The radiation is usually described as originating at he even horizon. The explanation makes sense and all, but still how can this locally non-special place become the seat of a local phenomenon(emitting...
Hello,
Theoretically any object can convert into black hole by compressing its mass below some radius( describe by Schwarzschild Radius). Suppose one of this object after becoming black hole have radius
which is comparable to atoms and nucleus radius. Now my question is what will happen if we...
Is it possible, in principle, for an experiment to distinguish between an ensemble of pure states and an ensemble of mixed states?
If so, how?
In particular, I am thinking of an ensemble of particles whose spin has been measured, one at a time, on the "Vertical" axis. The ensemble consists of...
Consider a Maximal (negatively) charged black hole. Can it have "flavor" or weak charge?
Suppose a muon collided with that hole. Would an electron be emitted?
What if electron neutrinos collided with that black hole; would electron neutrinos more likely be emitted as Hawking Radiation...
if I compress a heavy body to a very small point object such that its density is almost infinity, I get a black hole. but how can a point mass be a hole?
why do scientists call it a black 'hole'?
what I mean is, if I were to be pushed into a black hole, will I collide with that point mass?
Also...
In my thought experiment (it seems that others have asked a similar question, but I have a more specific question in my list below), we have a physicist outside the event horizon of a black hole. He has many entangled particles and sends some into the black hole.
Is / Could there be some...
Well read a post long ago about light
My questions are:
If light has no mass then how can it be suck in a black hole?
What exactly is redshifting?
What do polarizing glasses do?
Suppose you have a source of electron antineutrinos, and you arrange your apparatus so that a billion billion billion of them collide directly with a black hole. In principle, you could measure the change in momentum and energy from that occurrence.
Suppose you did that the next day. According...
So I understand that as a star begins to die, and begins fusion of H, He, C, O... it eventually reaches Fe which cannot be fused to create energy. Then the stars own gravity overcomes it's outward radiation and the star implodes, and eventually a black hole is created.
How can the star's...
Hey Guys,
so i was reading Hawking&Ellis a bit and still encounter always problems with the Penrose-Diagrams. Looking at the Penrose-Diagram for the rotating Kerr-Black hole (just one illustrating picture at the end) i come up the following question:
Why are there TWO regions III and III ?
In...
I'm a bit puzzled by the dynamics of things falling into a black hole. If I start with a test mass at infinity, it will fall freely into the black hole and reach the speed of light at the event horizon.
What happens if I throw something towards the black hole? Will it already reach the speed of...
I have been pondering black holes for some time and have had trouble with the problems presented simply because there is very little we can do to study the phenomena. I have always thought of a black from the outside looking in, or basically the only way we can hope to see a black hole. However...
I have a problem with the concept of a singularity, defined as something that has a property which is infinite. Infinities do not belong in our reality, and in my opinion are just hints that our understanding of the phenomenon is incomplete or wrong.
From my understanding, during the collapse...
In the view of Hawking radiation and entropy of black holes, the evaporation is continuous and at one point, there will be no singularity for the black hole. By relativity, if we reach a super massive black hole, then time would be relatively slowed down to a point that it stops (maybe?). Now...
I'm going through Kerr metric, and following the 'Relativist's toolkit' derivation of the surface gravity, I've come to a part that I don't understand.
Firstly, the metric is given by...
Information that is ordered can be compacted down to a single repeating unit i,e; 110055110055110055110055 down to just 110055 and this meant that it must have been highly ordered to be compacted down this far.
So could it be that matter is also highly ordered somehow and it can be compacted...
Hey guys
First real thread besides my introductory thread.
I'm a Danish student in what is somewhat equivalent to my junior/senior year in the american school system. That was a small attempt at school system conversion.
I'm writing a project about the black hole Sgr. A* in the centre of our...
We have a large mass, and we increase it slowly- dropping in one atom at a time. Will a black hole form suddenly, or will it gradually become blacker with the addition if each atom?
I assume that a mass marginally below the threshold must at least partially have the properties of a black hole...
Hey all this is my first post,
Everyone knows you can't enter a black hole because you'll be stretched/turned into noodles due to the immense change in gravity over small lengths. I was reading another thread on the physics forum and happened to come across an equation which would determine if...
I see that the formula for hawking radiation is related the the formula for unruh radiation. The accelleration experienced by a body yields an unruh temperature equivalent to a black holes hawking temperature with an equivalent value of g. The unruh effect happens at all accelerations, therefore...
If a large mass of matter and anti-matter collided to form a black hole, I assume they would anihilate and you would have a black hole made of photons. Now considering the black hole as a container of photon, there must be a net pressure pushing against the confines of the gravity.
The force of...
A substance of arbitrarily low density can form a black hole if there is enough of it.
So I took the mean density of the universe and calculated how big it would have to be to form a black hole. It's a surprising coincidence that the swartzchild radius in light years is the exact age of the...
##E= -T^uP_u ##,
where ##T^u## is the time-like killing vector associated with the Kerr Metric and ##P_u## is the 4-momentum of the particle. ##E## is the energy.
Outside the ergosphere ##T^u## is time-like and inside the ergosphere it is space-like. Therefore it can be arranged within the...
I know the original schwarzschild formula for finding the radius of the black hole, but what equation can be used to find its mass if you ONLY know its radius?
I have a question about equation 10.21 in "Exact Space-times in Einstein's General Relativity" by Griffiths and Podolski. The equation is the well know standard metric for multiple extreme Reissner Nordstrom black holes.
It has the below term:
(1+ sigma(mi/ri))
The point ri = 0 is of course...
I just saw The Theory of Everything, which is a Hollywood biopic about Stephen Hawking. Of course the physics content had to be watered down and made to serve dramatic and thematic purposes, but a couple of historical points seemed interesting and made me wonder whether they were real:
1...
As all of us know that in a vacuum the particle antiparticle pairs or the virtual particles are created violating the law of conservation of energy.
So even near an Event Horizon of a Black Hole virtual particles are formed. One of the particles gets sucked into the black hole but the other...
I've been searching over this and I don't quite get it yet. I just heard about this "z" parameter for gravitational red shifting and I thought it'd be fun to apply into the scenario of a solar-mass black hole.
The equation I looked at was (1/(2GM/c^2r)^0.5) - 1 = z
So, like, does the z parameter...
After reading:
I wondered about the following thing - is it possible to make a story in which there is a place for a habitable planet and a black hole? (I mean, I have one idea, but it does not end up well... ;) )
I see one additional limitation: the black hole was created in a supernova, so...