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.
There are twenty candidates, and the poll is divided into Parts I and II, each with ten. The poll is multiple choice so it's possible to vote for several papers. Please indicate the ones you think will prove most significant for future Loop-and-allied QG research. Abstracts follow in the next...
General Relativity predicted existence of Black holes. The theory of general relativity predicts that a sufficiently compact mass will deform spacetime to form a black hole. But The Chandrasekhar limit is the maximum mass of a stable white dwarf star. White dwarfs with masses greater than the...
When the star stops burning because heavier elements like Iron are formed in its core. Then the gas pressure stops and as you know the gas pressure helps keep a star in equilibrium because it provides pressure against the force of gravity. So Iron does not give off energy. So what stops the star...
This seems like a question that would be in the Relativity FAQ, but I didn't see it.
Briefly: I've seen the claim made that there is plenty of observational evidence for the existence of black holes. But I don't understand how, from the outside, one can tell the difference between a black hole...
I am sure this question must have been dealt with before but i can not find an answer:
What came first galaxies or black holes? How did supper massive black holes become so massive?
List of most massive black holes
http://en.wikipedia.org/wiki/List_of_most_massive_black_holes
It is said that black holes exist and are therorized to be very very abundant throughout the universe. These black holes are said to be sucking everything up around it, including light. It is also said that the universe is ever expanding, and that expansion is accelerating. How can the universe...
I'm trying to understand the ideas in this paper at a nontechnical level:
Laura Mersini-Houghton, "Backreaction of Hawking Radiation on a Gravitationally Collapsing Star I: Black Holes?," http://arxiv.org/abs/1406.1525
She says:
This work investigates the backreaction of Hawking radiation on...
Black holes have long captured the public imagination and been the subject of popular culture, from Star Trek to Hollywood. They are the ultimate unknown – the blackest and most dense objects in the universe that do not even let light escape.
And as if they weren’t bizarre enough to begin with...
Newtons Universal law of gravity equations are an excellent approximation when dealing with low velocities (i.e., velocities whose magnitude is much smaller than the speed of light) and when dealing with weak gravity fields (such as those found on Earth or around low-mass stars). The...
Here is what I have read:
carroll, sean from eternity to here
carroll, sean the particle at the end of the universe
deutsch, david the fabric of reality
gott, j. richard time travel in einstein's universe
greene, brian the elegant universe
greene, brian the fabric of the cosmos
greene...
I've been reading Kip Thorne's "Black Holes and Time Warps," and it mentioned something rather counter-intuitive; apparently, when material forms an accretion disk and falls into a spinning black hole, it increases the angular momentum of it.
Now, let's take a gas cloud, and put a spinning...
In How A Supernova Explodes, Scientific American, by Bethe and Brown, there is this passage.
Wow 10% of the mass equivalent of the neutron star. What an amazing number. But as I see it, the number of neutrinos should equal the number of protons in the pre collapse core material (which...
The event horizon, or schwarzschild radius for a black hole with the mass of the Earth is 3 km. But according to http://hubblesite.org/reference_desk/faq/all.php.cat=exotic, objects would have to be as close as about 6.2 miles (10 km) to the black hole's center before they began spiraling in...
The way I understand Hawking radiation is that black holes decay by sucking in anti particles from the virtual particle pairs that are created right at its event horizon. I also understand that these anti particles reduce the mass of the black hole instantly when crossing the event horizon? And...
I have fundamental question about what is called the “law of conservation of energy”.
We all hear about the tidal power stations which using the tidal power. The source of the tidal power came from the changes in the gravity field between the moon and the earth. Allegedly, because of the law of...
Dear all,
In one of his lectures,Prof. Susskind mentioned that the event horizon "bulges" forward to meet any incoming radiation or matter; and it is a property of Einstein field equations. I have not come across any such property, and if it exists, shouldn't it belong to the Schwarzschild(or...
Hi
Is someone interested in this topic ?
I'd like to share my idea with you, PF people. I also designed a "reverse geometry" to illustrate this paradoxical effect.
Thank you for your answer
Jean-Marc
Recently I have been researching black holes, and came across the "Schwarzschild Radius". The wikipedia page on Schwarzschild radius's mentioned that the Sun has a radius of 3km. If that is so, then how can that be so, as that would mean that light cannot escape it.
So when it said "3km", did...
Does quantum bounce provide a solution by which black holes could on some other side of the universe or in another universe create white holes
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Jim P
With this post I am hoping someone would be kind enough to lead me in the right direction.
I am a layman who knows little about the actual math behind physics, nonetheless I have developed an interest in it and wish to expand my knowledge base.
First question I have is if someone could...
Hello. I would like to know. Does matter when heading towards a black hole then crossing the
event horizon threshold reach the speed of light? I am guessing no. It simply crosses the threshold
and at a finite velocity heads toward the center of the black hole.
The escape velocity of a...
Ok, so if I were to travel towards a black hole at close to c, would the event horizon become visible?
Let us assume there are no stars, CMB, or any other luminous body in the universe.
Could Gravitons be causing this Black Hole turbulence?
http://perimeterinstitute.ca/news/turbulent-black-holes
In the article above they talk about how the Gravity around Black holes is bumpy or has Gravity turbulence. Does this discovery give any evidence to the undiscovered Graviton? Because...
It is my understanding that at the most fundamental level, a black hole is simply an object with a gravitational field so strong that there exists a sphere that lies outside the body of mass of that object from which the escape velocity is equal to the speed of light. In other words, a body of...
Is it still true that most if not all galaxies have at their center a Black Hole? And that the estimated gravity is about 10% of the total mass galaxies. And is it still true that all stars or 99 % of them are moving out and a way from the black hole. I was just wondering if these black holes...
by Dr. Ken Croswell
Astronomers staring across the universe have spotted a startling scene: three supermassive black holes orbiting close to one another, two of them just a few hundred light-years apart. The trio, housed in a pair of colliding galaxies, may help scientists hunting for ripples...
So according to Stephen Hawking, non-penetrable event horizons don't really exist.
So by the same argument the cosmic event horizon can't exist either right? Only an "apparent" horizon which may hold information from outside the visible Universe for a short while until it enters the visible...
Black hole A moves at slow velocity, and there's an Einstein light clock hovering near the event horizon.
Black hole B moves at high velocity, and there's an Einstein light clock hovering near the event horizon.
The black holes are identical. And the light clocks are at the same...
For my research on astrophysics for the summer, a professor gave me this assignment but I don't know where to start. The question is: What methods could be used to find the dark matter distribution around a galaxy's central black hole?
Not sure how speculative this is but thought it would be of interest-
http://www.iflscience.com/space/could-supermassive-black-holes-center-galaxies-be-wormholes
and the related paper-
http://arxiv.org/abs/1405.1883v1
Distinguishing black holes and wormholes with orbiting hot spots by...
Bear with me, I am (not even) a chemist.
This is something that bothers me for some time.
The larger the black hole, the smaller the density and the smaller the tidal forces. Supermassive black holes (expected to exist in centers of galaxies) have density comparable to that of water, and I...
I am no cosmologist, just purely curious as to what the explanations and if there are explanations currently to some of my questions:
If it was possible can one fly far enough around a black hole in all 360 degree angles, i assume yes one could but what the question leads to is, does it have...
If I observe two particles that are entangled enter two different black holes and wait, will there eventually be 2 entangled photons radiating out of the black holes or do the black holes take possession of the entanglement as the 2 particles enter their respective black holes and said black...
Hawking Radiation and the "Decay" of Black Holes
I have been doing a lot of reading and thinking about certain quantum mechanics so that I can try and wrap my head around how it all works. However I have come upon something that I cannot find a good explanation for.
I was reading about...
So, yeah.
Here I am, a fledgling Undergraduate Freshman at Brigham Young University. I've been reading Brian Greene's books, and darn, do I love physics. This was the semester I decided to change my major from Mechanical Engineering to Physics-Astronomy.
Well, one night, as some of this...
Has it ever been explored in science that the other side of a black hole could have caused the "Big Bang"? My thinking is that if a black hole sucks in matter and compresses this matter to a point where it can no longer contain it; would that not cause a collapse on the other end?
It has been...
Hi friends,
I was wondering about the following - in GR texts we always see these penrose diagrams and some line representing the horizon and all these timelike , spacelike curves and all that ... but the picture that I have of GR is just that of a smooth 4 manifold endowed with a metric . Can...
As the title says, do we have to have black holes for the universe to run? Every galaxy has a suppermasive black hole at its center. What if there were a star at the center of our galaxy? I guess it would have to be so big but that means the star would soon run out of energy and then explode...
Why is there a large Shapiro delay when a light beam passes a black hole?
Coordinate velocity of the beam is slowed down in a gravity field, except for the straight down component of the coordinate velocity?
Some part of the trip takes a long time anyway.
This paper, http://arxiv.org/abs/1402.3055 Black Holes, Firewalls and Chaos from Gravitational Collapse, reminds me why it is risky to get too close to a black hole. The authors suggest some the paradoxes posed by black holes may be a consequence of the cosmic censorship hypothesis. I may have...
The nuclear explosion occurs when the nucleus of atom of Uranium (of Plutonium) are split in two pieces by neutrons. These two pieces are repelled from each other due to (the same) positive charge; these pieces are moving quickly between other Uranium atoms, colliding with them. These collisions...
Yesterday, I read about Hawking's new proposal regarding the firewall paradox.
A more general thought about standard black holes occurred to me. Black holes including stellar black holes are of course always presented as if the event horizon is an invisible barrier, which the unfortunate...
I've posted a few threads over the years questioning the existence of black holes, and the response has been unequivocal defense of them...
http://www.nature.com/news/stephen-hawking-there-are-no-black-holes-1.14583
According to general relativity, if a remote observer monitors an object falling onto a black hole, (s)he will never see the moment when the object crosses the event horizon. Due to the time distortion, the falling object will hover over the event horizon forever.
With that in mind, how...
It looks like the case for primordial black holes as dark matter is drawing to a close: http://arxiv.org/abs/1401.3025, Exclusion of the remaining mass window for primordial black holes as the dominant constituent of dark matter.