What is Black holes: 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.
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...
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...
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...
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...
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...
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"
- -...
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...
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...
So Alice and Bob are hanging out near a really large black hole.
It's quiet. Nothing has entered the BH is a while.
Alice tosses Bob in and then waits long enough for him to collide with the singularity.
Of course, Bob is keeping time differently than Alice - so I rather doubt that the time...
The other day my friend asked me a really interesting question regarding the scene from interstellar where they go down to Miller's planet, where every hour on this planet is 7 years of Earth time. He asked me if they were to send a signal to the spaceship where Romilly was, what would happen...
Here is a presentation on the discovery of two colliding neutron stars and the resulting phenomena such as gravity waves, gamma ray bursts, and synthesis of high atomic number elements. The author is a theoretical physicist who is involved in the research.
He says that the neutron stars most...
Recently there have been a lot of studies of black holes colliding and the gravitational waves that they produce. My question is: What is the effect on the space between the two black holes before they collide. The stress must be extraordinary. That stress should be measurable by radiation...
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...
How long would it take for an object, stationary with respect to a black hole (mass of the sun), to fall from 1 AU into it beyond its event horizon?
From our frame of reference can we observe over time, a black hole growing in size as matter falls beyond the event horizon?
From our frame of...
The thing is that this is an exercise that I have to show my teacher but I don´t know how to get the answer.The exercise says:
"A body of mass m moving in the Keplerian field V = −M/r (in G = 1 units) has a total conserved energy, Etot = 1 /2( m r˙^2 + r ^2ϕ˙ ^2 )− mM/r.
Show that the...
The laws of physics breaks down at an atomic level, it also breaks down around black holes.
could the two be related? could a black hole be an atom with a periodic number in the (insert ridiculous number here) ?
If it were true that black holes where atoms / elements it'd turn two problems...
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...