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.
Hello, I didn't know if this is the right place for this question but here it is. I have a thesis due by June sometime. The thesis is in an astronomy course so I would like to do something on physics. I have just started learning the basics and would like to impress the teacher (this might help...
I'm a structural engineer in Mississippi and I love all aspects of cosmology. I want to learn all I can about gravity wave technology. I was not expecting the level of detail that a single event is revealing. It's very interesting that they expect to see gravity waves from objects other than...
Questions.
1. As protons will eventually decay, will objects made with protons orbiting black holes that are time-dilated remains?
2. What happened at someone's perspective if he/she fell into a super massive black holes? Will he/she be free instantly? (Time dilation)
3. What happens after the...
Is there a limit as to how much a black hole gathers mass and how much it losses mass via hawking radiation so that the black hole becomes in equilibrium, neither gaining mass or loosing mass
How long would it take a hypothetical isolated black hole to loose one solar mass due to Hawking radiation.
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...
When I saw the report of a gamma ray burst associated with the LIGO GW event, my immediate thought was that the obvious explanation is that the compact massive objects were not in fact black holes, and the gamma ray burst was from the energy of the final collision and merger.
This would...
Quite unexpectedly, it seems that the Fermi Gamma-ray Burst Monitor spotted what appears to be a hard gamma-ray burst about 0.4s after the LIGO GW event, lasting about 1s: http://arxiv.org/abs/1602.03920
This is not expected from a black hole merger (and as a black hole sceptic, I find it very...
As we all know, the LIGO collaboration published a paper recently on the first direct observation of a binary merging black hole system. From the observed signal, they were able to infer the black holes' masses and their distance from Earth.
However, the fact that they can estimate masses and...
a related thought experiment to a tunnel through Earth through which a person falls to the other side, is what if it was a pendulum falling through the planet?
first, a pendulum is at 90 degs to the G field; 2nd, as soon as the pendulum BEGINS to fall through, it is in free fall, and it will...
OK, in solar mass terms, 29+36=62 with 3 left over. Or make that 3 left out.
This is a little-advertised mechanism for pulling mass from a black hole. And, since the output is gravity waves, it doesn't seem to be directly related to Hawking Radiation.
Somehow intense gravity can scoop out...
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...
Since we think that 85% of the matter in the universe is Dark Matter, does it follow that around 85% of the mass of a typical black hole should be of dark matter origin?
If not, why not?
And if so, black holes are defined by only 3 parameters, mass, electric charge and spin. As far as we can...
It appears that black holes do exist in our universe, in the sense that there are objects so massive and so small that there must be an event horizon. Is it generally accepted that there is "really" a singularity inside these event horizons, or that we just don't know, and may never know?
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...
First of I am not a scientist, just a big fan. So I am sorry for any incorrect terminology. A few years back I remember reading a article on the various theories pertaining to Dark energy. I think it may have been in a Scientific American. After the article was done talking about the most...
The tittle says it all really, how did Black Holes appear so early in the universe, why not stars?
arXiv:1601.05473 [pdf, ps, other]
The Early Growth of the First Black Holes
Jarrett L. Johnson (LANL), Francesco Haardt (Universita dell'Insubria)
Comments: 13 pages, 9 figures, invited review...
I don't know if this question makes any sense, sorry if it doesn't.
I have often read that any matter (say an object, for more mundane clarity) falling into a black hole (providing it radiated) would be perceived by an outside observer as never actually crossing the event horizon. It's "image"...
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...
Soft Hair on Black Holes
Stephen W. Hawking, Malcolm J. Perry, Andrew Strominger
(Submitted on 5 Jan 2016)
It has recently been shown that BMS supertranslation symmetries imply an infinite number of conservation laws for all gravitational theories in asymptotically Minkowskian spacetimes. These...
Apparently rare - only 12 galaxies are known to exist with two black holes in their midst, according to Dr. Julie Comerford.
Comerford reported a recent observation of a double black hole galaxy at the American Astronomical Society's annual meeting in Kissimmee, Florida. One of the BHs is...
If a black hole had a mass similar to the Sun (I know black holes tend to be at least three times larger but let's assume an unusual series of events) how far would the are of extremely distorted bent gravity around it be could it cause closely orbiting bodies to be pulled or pushed out of orbit...
Hey guys. I've been wondering, what would happen if a star around 13 solar masses and a black hole 10 solar masses were drifting towards each other? Since the star is heavier, It would absorb the black hole, But i think when it reaches the event horizon It would meet Mr.Singularity, and what...
Over the years I've watched Science try to deal with the Information Paradox regarding black holes.
http://news.sciencemag.org/physics/2015/12/physicists-figure-out-how-retrieve-information-black-hole
I've always been curious how we got to the point where we see this as a problem in need of a...
Why is it that the smaller the black hole is, the more quickly it supposedly evaporates? It seems like a black hole should radiate energy proportional to the surface area of the event horizon. To me it seems like the evaporation should slow down the more the black hole shrinks because the energy...
What do you think about the following blog post about a recent paper by Alex Vilenkin about the possibility of black holes containing inflating universes?
http://fqxi.org/community/forum/topic/2589
According to LQC, did the universe before the bounce contain black holes? If so, would they still be around?
What I'm getting at is this: I've read that LQC predicts that the high densities around the bounce tend to smooth out inhomogeneities. If I understand correctly, this is quite promising...
self-dual loop quantum gravity results when the immirizi parameter y=i has been the subject of many recent research papers here is a partial listGravitational axial perturbations and quasinormal modes of loop quantum black holes
M.B. Cruz, C.A.S. Silva, F.A. Brito
(Submitted on 26 Nov 2015)...
Hi, layman here,
I have often read that because of time dilation, we would never see any infalling matter actually crossing the event horizon, it would just look more and more redshifted towards becoming invisible, even for infrared or microwave / radio detectors, but never becoming part of the...
http://www.space.com/28664-monster-black-hole-largest-brightest-ever.html
Astronomers have discovered the largest and most luminous black hole ever seen — an ancient monster with a mass about 12 billion times that of the sun — that dates back to when the universe was less than 1 billion years...
I have heard that, given the energy of a quantum of Hawking radiation, we can extrapolate backward in time to its 'creation' near the event horizon. When we do this we find that, because of time dilation and conservation of energy, the wavelength of the emitted particle becomes smaller than the...
I understand how the neutron stars are formed, and why the electron degeneracy pressure collapses as electrons are absorbed by protons, by photo disintegration. However, I'm struggling to grasp what happens when the gravity is large enough to overcome neutron degeneracy pressure.
Apparently a...
So, according to physicsoftheuniverse.com, "In the centre of a black hole is a gravitational singularity, a one-dimensional point which contains infinite mass in an infinitely small space, where gravity become (sic) infinite and space-time curves infinitely, and where the laws of physics as we...
[Moderator's note: Spun off from previous thread on different topic.]
I'm still a bit new here and haven't studied much astronomy (being an electronics dude) so can anyone give me a good link(s) for what we know about existing black holes. That is size, location, and other physical...
For this we need a thought experiment: imagine you're on a gedanken planet manning a gedanken laser cannon, and it's pointing straight up. The light doesn't curve round, or slow down as it ascends, or fall down. It goes straight up. Now let's keep you safe in a bubble of artistic licence, and...
http://arxiv.org/abs/1510.03066
String condensation: Nemesis of Black Holes?
Michael Hewitt
(Submitted on 11 Oct 2015)
This paper puts forward a conjecture that there are no black holes in M theory. We will show that a mechanism to prevent black hole formation is needed in 4 dimensions to make...
Homework Statement
Muscle can be torn apart by a force of 100,000 N applied across an area of 1 m2. A 10 cm2 muscle therefore will be torn by a force of 100 N.
If a student of average size were being lowered into a black hole of 1 solar mass, at about what distance from the hole's center will...
This paper;http://arxiv.org/abs/1510.01733, Detecting Direct Collapse Black Holes: making the case for CR7, announce potential detection of a direct collapse black hole. Such a detection would shed light on questions such as the origins of SMBH and galaxies in the early universe.
Do these PBHs exist and would they lead to quantum gravity?
http://arxiv.org/abs/astro-ph/0504034
Recent developments in the study of primordial black holes (PBHs) will be reviewed, with particular emphasis on their formation and evaporation. PBHs could provide a unique probe of the early...
Here is an oddball that I am wondering -
could the spaghetification be countered by time dilation? Because as you approach a black hole (assuming you go in legs first) not only do your legs experience higher gravity than your torso, but they are also subjected to more time dilation - as they...
It heard it stated that light cannot escape from a black hole, yet light continues to propagate at the speed of light even in a black hole. Can someone explain to me how it can be that light can't escape yet does not slow down?
Hi Everyone,
first post here, another enthusiastic amateur I'm afraid so please excuse my general ignorance!
I struck me the other day that it should be possible to find an arrangement of large galaxies that would allow light emitting from our galaxy to be bent back towards us. This would give...
If they are so insanely dense and their gravity is so mind-numbingly great, what prevents a neutron star from immediately collapsing into a black hole?
I have some questions regarding things that boggle my mind about black holes. These things seem to me like paradoxes, and I was wondering if someone could explain them.
1. How do you measure the distance to a black hole? As far as I understand the distance to a black hole is defined as the...
My professor wants me to make a 15 minute oral presentation on black holes for an event we have going on on campus. How should I structure it? I think I have a pretty good understanding of the concept of a black hole, but I don't want to get caught off guard during the 5 minute Q&A section. My...
The Einstein-Cartan theory is, to my mind, a completely straightforward generalization of General Relativity, and indeed seems like a necessary generalization if we are to accommodate particles with intrinsic spin. (The mathematics for this claim is beyond me, but the layman's summary is this...
I'm very new to the understanding of Hawking Radiation. I don't know much about this theory, but I do know that Hawking radiation works on a Quantum scale. I know that with black holes this theory proposes th idea that over time black hole lose mass because of "Spontaneous appearing positive and...
According to Hawking [1] it is posited that light photons at the event horizon of a black hole must cease to move, and remain motionless for the entire lifetime of the black hole.
It is also observed [http://dls.physics.ucdavis.edu/~scranton/LensedCMB/a2218.gif] (and calculated) that the path...
this paper
Do Black Holes End up as Quark Stars ?
R.K.Thakur
(Submitted on 25 Feb 2007)
The possibility of the existence of quark stars has been discussed by several authors since 1970. Recently, it has been pointed out that two putative neutron stars, RXJ 1856.5 - 3754 in Corona Australis...