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.
Homework Statement
Consider a 2D spacetime with:
## ds^2 = g_{tt}dt^2 + g_{tx}(dtdx + dxdt)##
where: ##g_{tt} = -x## and ##g_{tx}=3##
Draw a spacetime diagram showing the null geodesics, including one which passes through the origin. Then show that for a massive object, when ##x## is positive...
Now my Kerr orbit simulator is pretty much feature complete, I have started to look at producing videos . . .
I have just started a channel on YouTube to accumulate some of the more interesting examples. Aside from creating the simulation, the most difficult part was to generate useful initial...
I have a simple question about Lewkowycz and Maldacena's paper http://arxiv.org/abs/1304.4926v2'][/PLAIN]
http://arxiv.org/abs/1304.4926v2
In section 2, they consider the scalar field in BTZ background ground and require boundary condition of the scalar field,
$\phi \sim e^{i\tau}$ . This...
OK, so it's time to start a new thread.
I heard many times that there exists only one black hole solution for a given mass and angular momentum, but I know already that this is not true.
We all know that if we throw something into an existing black hole, its event horizon starts to ripple. So...
How is information conserved when one form of energy is converted to other?
Like how a black hole's gravitational energy is used to create photon pairs near the event horizon, what happens to the information in the gravitational wavepackets (gravitons?) and how is it not lost?
A black hole evaporates through hawking radiation, what I don't get is the requirement for an energy-negative energy pair production. Since it's the black hole's gravitational energy that's responsible for the pair production, even if one of them escapes, the black hole would lose energy anyway...
Assume a spherical black hole that is eating matter from its surroundings. Then its Schwarzschild radius will increase with a speed proportional to the mass flux that enters the black hole. The question is: is this speed limited by the speed of light in vacuum c?
If the event horizon is a...
This is a somewhat weird question, but here it goes:
What would happen if there were only gravitons? Would some other kind of particle appear in the Universe sooner or later? Would there be any chance for mass to appear in such a Universe (assuming that the graviton is a massless particle)...
In a couple of recent threads, I have attempted, unsuccessfully, to elicit a response to the following, which is my belief about why an observer standing well off from a black hole will in fact see the black hole evaporate (over a LONG period of time, of course, so the observer has to have an...
Premise 1: From the frame of reference of the earth, observing a thing falling into a black hole (crossing the Schwarzschild radius) is impossible -> the thing is observed falling toward but never reaching the radius, i.e. the process takes an infinite amount of time.
Premise 2: Observation...
What would the final velocity of an object be as it falls into a black hole? I assume you could calculate the gravitational field strength of the black hole to determine the acceleration of the object and then calculate the final velocity with the equation
V(final) = gt + v(initial)
Can someone point me to the seminal (or any other) paper explicitly showing and proving the formation of singularities in black holes?
I'd like to learn about the exact physical processes which occur during the collapse of a star into a black hole and how the progress of those physical...
I was wondering what is known about the speed of objects falling to the centre of a Black Hole?
If a number of identical objects, initially located outside the event horizon, were propelled at varying speeds towards a black hole, would that variability be maintained as they pass through the...
I was wondering about this for awhile and I still don't understand what happens to the enormous amount of mass stored in a black hole when it dies. I understand this question is based on a conclusion that may be incorrect, but if anyone could shed some light on this, please do so.
In various explanations of the event horizon which do not invoke the existence of a firewall (thereby upholding the dictum that an observer would not notice any difference upon passing the event horizon until she looked out the window), one uses the concept of a theoretical observer passing the...
HI,
I need to calculate the variance of mass released when a particle jumps down or up between energy levels
inside a black hole , i don't know where to begin
any advice will help
thanks
If the sun disappear right now, we won't notice before 8 and something minutes due to the speed of light. The Earth will keep going it's way on it's orbit because, as everything, gravity cannot exceed light speed.
The same would apply if we were orbiting à black hole.
I often heard of the...
I am reading about mergers of a neutron star with a black hole and the association with GRB. While talking about the accretion disk, the paper I am reading says about the last stable circular orbit.
Firstly I thought it was where the Roche limit lies, where mass transfer or matter ejection from...
If we plug the Planck mass into the Bekenstein-Hawking formula for the BH entropy, we'll get S = A/4l^2 = 4πGM^2/cħ = 4π ≈ 12.56 nat for the minimal Schwartzschild black hole.
If we assume that each entropy unit is a compact area on the horizon, can we consider the minimal BH a dodecahedron...
I have a question that when the fuel of star runs out there is a imbalance is temeperature-gravity equilibrium.
When it collapses to a single point where mass gets compressed so much,but shouldn't the temperature at instant increase so much that the mass could not be compressed to infinite...
Naive reading on the web says that stellar collapse is halted by quantum mechanical processes called "degenerate pressures" that arise when gravity tries to force fermions such as electrons or neutrons into the same quantum state. White dwarfs are propped up by electrons, neutron stars by...
[Mentor's note: The thread title has been edited to change the level from "A" to the more appropriate "B"]
Suppose there is planet Z revolving around black hole. Astronaut from Earth go in that Planet Z and start video recording and make a DVD . Suppose they played that DVD in the computer in...
The question is as follows: suppose I throw a metal bar 1m long inside the event horizon of a supermassive black hole of 1 million solar masses. At both ends of the metal bar there is a light source.
(I chose a supermassive black hole to rule out any spaghettification process: with some quick...
I've recently read a new article that said that the recent gravitational waves might have had 2 black holes in a star
that gave me a question, because you need masses to move or accelerate to generate gravitational waves, what happens to the mass inside of the star? because black holes's space...
I refer to the time coordinate of an outside observer (ideally hoovering over the BH at large constant distance). Can (s)he actually see something falling into the hole within finite time, that means actually disappearing and making the Event horizon larger? If no, all the merging of black...
According to the holographic principle, It is proposed that the entire information that is kept in a 3D volume of the black hole can be represented in a 2D surface of its horizon. What if we have a drunk falling into a black hole and moves in a random walk in his inertial frame. According to the...
(1) Maybe should've messanged this, but given LIGO, the FAQ might need a light edit. It says,
"Gravitational waves have never been detected directly, but the loss of energy from the Hulse-Taylor binary pulsar has been checked to high precision against GR’s predictions of the power emitted in...
light waves created inside a black hole cannot. Can gravitational waves escape from inside of black holes?
in classical GR. does the answer change in string theory?
Hi Folks,
Can somenone explain what "information" is with respect to black holes?
I thought it was all about mass and energy from both quantum Mechanics and GR perspective.
Why does "information" come into it...sounds unusual to say the least.
Thanks
B
This question is in context of the recent gravitational wave detection by aLigo. Apparently aLigo has detected the entire process, including the before merger, during merger, and aftermath of the completed merger.
My understanding is that two black holes should not be seen to be merging in...
http://cdn4.sci-news.com/images/2016/02/image_3628-Gravitational-Waves.jpg
In the above image, i can see that the event horizon of each black hole has decreased in size. Does that mean that the event horizon can shrink in the presence of another black hole?
And how does graviton escape the event horizon? People say it's because those gravitons are "virtual particles" and can travel faster than light, yet many of the posts i read on here say virtual particles don't even exist. Also, gravity TRAVELS at the speed of light, if the sun is suddenly gone...
This picture confuses me. It showed here that the red particle at top right get suck into the black hole. But to a distant observer, everything near the black hole get time dilation and finally freeze at the horizon, right? So, "when" the black hole evaporates?
Moreover, why the black hole likes...
Hi.
From an outside observer's view, any object approaching the event horizon of a black hole appears to slow down and never quite pass through the horizon. So information about those objects can always be retrieved (if you correct for the redshift). So what actually is the information paradox...
Would it be possible that you could create a black hole from heating something really hot. I heard Vsauce said if you heat something hot enough that it's wave length of the light released is smaller than the plank length, it would become a black hole. That means that the energy would be on the...
Is this the proper formula for calculating the Schwarzschild radius of a black hole?
rs = 2GM / c2
If it is not, or if anyone has one that might work better, could you refer it to me?
Hello,
I'm working on a hypothetical situation involving a planetary body orbiting a black hole (similar to the scenario in Interstellar, but for different reasons), trying to balance tidal forces with orbital distance and time dilation.
First, I'm interested in the effect of gravitational...
[I originally posted this in Astronomy and Astrophysics but it didn't get much traction. Perhaps folks in this forum would have something to contribute...]
I'd like to understand if and when information is ever actually lost in a black hole; specifically, I'd like to analyze the statement:
Is...
This paper; http://arxiv.org/abs/1601.05473, The Early Growth of the First Black Holes discusses the evolution of supermassive massive black holes [SMBH] as inferred from observations of high z quasars: which has provoked questions about the putatitve age of the universe and the time it allows...
I'd like to understand if and when information is ever actually lost in a black hole; specifically, I'd like to analyze the statement:
Is there information, which existed in the past, that is theoretically unavailable to external observers today due to falling through the event horizon of a...
Hi. Now that I understand the conservation law of angular momentum, and given the fact that c is constant, I infer that if a photon were to go into orbit around a black hole, it could only take a circular orbit. No elliptical orbits for photons, because if it were to follow an elliptical orbit...
I have just seen a brief clip of an article by a journalist regarding a lecture given by Hawking this week about the mystery of where information of a star goes to when it is swallowed by a black hole. As a non physicist, I am grappling with what exactly is meant by this. Isn't this just a...
Since the center of a black hole is defined as a singularity and space-time collapses at that point (assumption) is it possible to define this point in 3D coordinates? In other words, is it possible that our universe can not be described as a 3D space but rather as a space with 2.99... dimensions?
Signature of an Intermediate-Mass Black Hole in the Central Molecular Zone of Our Galaxy - arXiv 1512.04661 (free reprint)
Apparently there was another thread with a similar title ("Second black hole may lurk at Milky Way's heart") from June 2003, but it really had nothing to do with a second...
What would happen if you were to fly a starship traveling near the speed of light directly into a black hole?
Would it stay in tact because it cannot be accelerating any faster?
Or would it split because it's being accelerated in all directions simultaneously?
I feel like this could go in quite a few of the Physics subforums (Quantum Physics, Beyond the Standard Model, Special and General Relativity, or High Energy, Nuclear, Particle Physics) instead of Astronomy and Cosmology, but hopefully this will work. This is my first question I've posed here...