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.
Dear PF Forum,
I have read a link about big bang time line. Started from time zero, then Baryogenesis, lepto genesis, Planck time then on...
http://www.physicsoftheuniverse.com/topics_bigbang_timeline.html
I try to make a simple calculation here with Schwarzschild calculator.
The mass of the...
Since light is entirely incapable of slowing down, what happens when light approaches a black hole such that it's trajectory passes through the exact center of the black hole? It seems, based on what I currently know, this would mean that the gravitational force pulling on the light would be in...
[Moderator's note: Spin-off from another thread.]
I'm sorry, does black hole have surface area? Did you mean the sphere defined by Schwarzschild Radius?
I'm just curious, do black holes have a maximum size? In other words, if it theoretically had an infinite supply of matter to "feed" off of, would the black hole just get more and more massive or is there a point where it can no longer fit anymore matter? Will it just spit out hawking radiation?
Hello people,
I have a question regarding black holes. The way i understand it, black holes form in supernovas, and they occur because the gravitational pull of the stellar remnant is so great that nothing can stop it, and it basically collapses down to a singe point, virtually nothing...
Now...
Dear PF Forum,
I have no background in physics :frown:
In http://math.ucr.edu/home/baez/end.html
1. If an Earth size object is left alone (assuming the Sun won't swallow it 2 billions year later). In 101500all of it atoms, oxygen (majority abundant in earth, right), silicon, nitrogen (abundant...
Questions about black holes:
Various articles mention that it takes infinite amount of time to observe something pass through the event horizon.
Does this imply that the redshift observed from afar would carry on forever, that the infalling object would just become dimmer and dimmer, but never...
We all know from the relativity, that even the light gets into the black hole, so gravitation-gravitons(what is actually graviton?)are stronger than photons in this case!?
I want to know which dimension does the black hole belongs? Can anyone say which force is responsible for the absorption? In case, if the black holes absorbs everything then were the things might gone?Is that everything becomes invisible or just blast into pieces?
Forgive me if I have posted this in the wrong location. I'm trying to reconcile my understanding of spacetime, but am running into a paradox that I'm sure is arising from my own misunderstandings. As you get closer to a black hole, time, with respect to outside observers, begins to slow to a...
Hi all,
I am currently reading a paper and they have this statement in the abstract:
"If the supermassive black hole Sgr A* at the center of the Milky Way grew adiabatically from an initial seed embedded in an NFW dark matter (DM) halo, then the DM profile near the hole has steepened...
Normally a star with a mass several times that of the sun will become a black hole at the end of the lifetime of that star. Can black holes exist with a mass much smaller than that exist? In other words, are black holes with a mass of Jupiter or even Earth exist? Or even much smaller than that...
Does gravity get destroyed in a black hole ? If the Higgs particle creates mass in the universe and higgs are destroyed in a black hole, then the total gravity in the universe must diminish over time , hence the universe expanding ?
Homework Statement
I am preparing a report on black holes and I recently learned about a phenomenon I was previously unaware of: the photon sphere of a black hole. While reading an article on said occurrence (I have now confirmed this on multiple sources) the photon sphere which is the minimum...
Good morning everyone, I'm Giuliano and I would like to know how light behaves in a black hole and because it can not get out.
More precisely, i understand that light moves in curved space-time format from the black hole, but once passed within swarzchild radius the photon is expected to impact...
I've been working through Leonard Susskind's "The Theoretical Minimum" lecture series (which are a fantastic introduction to the topics covered by the way) and a couple of his comments confused me when he was covering the Kruskal-Szekeres metric/coordinates in General Relativity.
The end of the...
We know that light's speed gets slowed down when traveling through a medium, and the more dense the medium the slower light can travel (of course c remains constant, but it takes longer to travel due to the continuous scatterings, absorbtions and re-emissions).
Inside a black hole, just below...
The dinamic of a light ray in a Schwarzschild' s metric is governed by a lagrangian where the potential is V(x)= a*(1/r)^2-b*(1/r)^3 with a and b positive costants.
The presence of a Lagrangian it means that is possible to apply a first quantization of this sistem; if so which are the...
Hey so i have a naive question that i always had since i was young, but i never really could find an answer to it.
Lets say you have a black hole isolated in a vacuum, in a closed system.
Dark matter is supposed to be a sort of weakly interacting massive particle, which exerts a gravitational...
Homework Statement
Trajectories around a black hole can be described by ## \frac{d^2u}{d\theta^2} + u = \alpha \epsilon u^2 ##, where ##u = \frac{1}{r}## and ##\theta## is azimuthal angle.
(a) By using ##v = \frac{du}{d\theta}##, reduce system to 2D and find fixed points and their stability...
Question!
So Alice falls into a black hole, instead of the volume increasing for the black hole, it actually increases proportional to it's area. Thus one can draw the conclusion that 3 dimensional information can be fully explained by the information encoded on the surface area at the boundary...
What is the size of the singularity?
1. Is it 0 cm?
2. Is it below Planck length?
3. Is "the size of singularity" the wrong question, such as asking "what is the length of 500 celcius"?
What does that mean?
From event horizon all the way, just before, the centre, is vacuum?
And suddenly there...
Hello,
I had a thought about the formation of white holes off of black holes and i wanted to ask if it is possible,
if a massive black hole is surrounded by a lot of matter(a lot of giant stars etc.) and it consumes so much matter that even a aquasar is not sufficient enough in disposing all of...
Dear PF Forum,
In less than 1 second after big bang, baryons were created. And there's asymmetry in it.
Can anyone help me?
1. Is it physically possible for a galaxy made entirely from anti matter?
2. If it's true, is it statistically possible for a galaxy made entirely from anti matter?
If...
ok, hear me out on a lymph, because I'm going to either be talking crap or something that sounds crazy
either way...
my question is:
why does the phenomena of a black hole look so perfectly circular/spherical?
now here's my reasoning
spheres are the shape that takes the least energy to be...
Homework Statement
A sub-atomic particle is near the event horizon of a black hole. Due to the nearby gravitational field, the Ricci Curvature Tensor is changing rapidly. The particle then performs quantum tunneling. Homework Equations
Which version of spacetime does the tunneling particle...
I still don't understand this fully. Can someone please explain? I saw a video where an analogy was made, the distant observer is like an accelerating observer in flat spacetime and guy falling in is like an inertial observer, is it just like the coordinates of the distant observer from the...
Can someone please explain what a black hole is? I hear everyone speaking about it but have no idea what it is.
Is it something where even speed of light becomes 0? How?
Hi,
Einstein once showed that if we assume elementary particles to be singularities in spacetime (e.g. black hole electrons), then it is unnecessary to postulate geodesic motion, which in standard GR has to be introduced somewhat inelegantly by the geodesic equation. I don't have access to...
I've read that a stellar-mass black hole has a lifespan on the order of 10^67 years. Does this mean that a clock which is at rest with respect to (and sufficiently far away from) a stellar-mass black hole will tick off 10^67 years before the black hole evaporates? Also, will shell observers...
Hello all, please forgive me if I seem somewhat unaccustomed to this site, I have just registered.
I suffer from an illness called catastrophic thinking syndrome, simply put this means that I turn everything I read into a disaster until I become ill due to anxiety / depression . I recently...
Sorry for a bit of a sci fi question but are anti matter black holes likely, presumably they would need to come from whole antimatter stars in antimatter galaxies? otherwise they would already have destroyed themselves?
this seems like a dumb question but i just can't think of a solution. black holes can suck photons, that's why they are black. but there are charged black holes, and the EM forces is mediated by photons, so how can the mediating photon escape the gravity? also arent the gravitons (i know...
Hello to all !
I wanted to ask a question in this forum. I am french, and I have discussed this topic in a french physics forum, but with no clear conclusion. I hope I'll have another insights in this forum, which seems very well frequented.
I know the underlying subject has been discussed in...
I was thinking today about black holes. I was imagining how they formed a singularity, not mathematically, but physically and I got stuck at the Planck density. It's not a singularity yet and even with the entire weight of the rest of the object on top of it, you shouldn't be able to pack more...
I need to find the vectors for time and radius that describe a space-like 4-acceleration of an observer falling radially into a spherically-symmetric black hole. Previous to this question, the values of the real time derivatives for time and radius were derived to be:
dt/dτ = (1-2m/r)-1
and...
I'm currently teaching a gen ed course called Relativity for Poets. This is the first semester I've taught it, and it's been a ton of fun so far. If anyone is curious, http://www.lightandmatter.com/area3phys120.html is the class's web page with links to the syllabus and lecture notes. The...
The force in the centre of the earth, assuming it was a perfect sphere and the density was the same everywhere, would be zero as the pull from all directions would cancel. Why isn't it like this for a black hole? Surely the forces from each direction should cancel leaving zero resultant force at...
Would the universe end if you entered a black hole? What I mean by this is that due to time dilation would time elapse so fast for the universe outside the black hole relative to you inside it that all the stars would burn out and all that wouild be left would be other black holes?
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.