What is Blackholes: Definition and 72 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.

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  1. Mlesnita Daniel

    I What kind of matter formed Primordial Blackholes?

    I read somewhere "space was not completely homogenous (the same at every point). Instead, some areas were denser and hotter than others, and these dense regions could have collapsed into black holes." and I was wondering what does it exactly means? Did space itself fall into becoming PBHs...
  2. J

    B Descending a Black Hole: Spaghettification or Compression?

    I have heard from, many attractive looking physicists on Youtube, that if I fell into a black hole, as I fell, I'd be stretched out or be "spaghettified. Is this correct? It seems to me that gravity compresses the free space, and that means, any object near a black hole should be compressed. If...
  3. Mlesnita Daniel

    B Could singularities be just rips in the space-time fabric?

    First off, this is just an assumption. My knowledge of the field is extremely limited and I beg you to come and correct my mistakes, so I can learn. So, I guess we all know how that space-time fabric is bended by gravity. When a star dies, all of the atoms are brought extremely close...
  4. tuantle

    I Origin of supermassive blackholes in the very early universe

    Hi, I am new here. A while back I read articles about observations of supermassive black holes in the early age of the universe. What are the hypotheses that would explain how these black holes grew so large and so fast so soon? Could inflation play a role here? Like how inflation would be able...
  5. marcelhattingh

    B How do we know we are not inside a blackhole?

    If you fall into a black hole, that what is closer to the singularity, will fall faster that than what is further. However, space before and after you, is falling in with you. So from each General Relativistic perspective of "you", because there would be no inertial frame to orient yourself (you...
  6. 1

    What Happens to Mass When Black Holes Move?

    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...
  7. ganguly pranav

    Black Holes, Light & Photons: Mass & Speed

    If black holes were able to stop light from escaping , then would it mean that photons do have a certain mass (no matter how much negligible it is ) and if it does then how can something that has mass (photons) travel at the speed of light. wouldn't the speed limit aplly to them too?
  8. Justice Hunter

    Particle/antiparticle annihilation problem near blackholes

    So around the time of the Big Bang, Particle and antiparticle pairs were created and annihilated. I believe one out of every 100 million(?) particle pairs actually didn't have an accompanying antiparticle, and survived the maelstrom, giving us the galaxies and stars we have today. Now, at the...
  9. A

    Black Holes: Gravity & Formation Explained

    Do black holes have gravity less than their mother star?.if no then why not,though during formation of black holes outer layer of star explodes out in space and inner core crush by its own gravity this way its mass decrease..So If i consider Gravity a force,by Newton law of gravitation Decrease...
  10. M

    Light & Blackholes: Unraveling the Mysteries

    Well read a post long ago about light My questions are: If light has no mass then how can it be suck in a black hole? What exactly is redshifting? What do polarizing glasses do?
  11. D

    ULXs & Black Holes: Unveiling Secrets of Escape Velocity

    Scientists had long thought that black holes were the only sources for ULXs. As black holes consume nearby material, they emit powerful X-rays thought to be responsible for the extremely bright ULX objects. http://www.space.com/27385-pulsar-discovery-superbright-xray-beacon.html A few...
  12. S

    Do Black Holes Outlive Everything Else in the Universe?

    Hey all, This is a just for fun question, as I am sure there is no definitive correct answer. But here it goes Blackholes to my knowledge, generate the strongest gravitational fields in the known universe. While thinking about gravitational time dilation, and the sheer magnitude that black...
  13. T

    How do we know blackholes are dense? Could instead they be a vortex?

    I was wondering if we decided that black holes are dense due to the spin and gravity? Are there any other factors for determining density? And could those factors also be true if a black hole were simply a vortex- like a drain per se. A drain that shoots out in two opposite directions, that...
  14. M

    How Blackholes Influence Outside Event Horizon: Exploring the Theory

    I just registered and am not entirely sure this is the right section of the forum to ask, but regardless... My understanding of gravity is that it is a wavelike distortion in spacetime which travels not instantaneously but at the speed of light, and may also be describable in terms of a stream...
  15. R

    Matter ingestion rate of blackholes

    Sorry if my questions are rather naive, this is my first post on this forum. Whilst burshing my teeth, I was watching water drain from the sink and came up with a few rather curious questions. Does the ingest of matter suggest by black holes suggest that the pressure of our universe is...
  16. L

    Are there non-spherical blackholes?

    An amount of material I have read recently refers (specifically) to the spherical case of black holes. Are there non-spherical black holes? Regards, Noel.
  17. I

    The philosophy of Wormholes, Blackholes, Deep space, etc

    Many scientist have actually wondered what scientific discoveries await from the beginning of a wormhole to the bitter end on the other side. But what exactly can be waiting on the other side at the very end of that dark abyss? What do we truly know about the deep regions of space and time...
  18. G

    Why do blackholes cut off from the rest of the universe

    This is from Hawking's Brief History of Time: I don't see why the black hole is cut off from the rest of the universe. The black hole is still there and it's still made of ordinary matter, just a more dense than other matter. Is it because time stops in a black hole? Or that nothing can...
  19. R

    Quarks can form mini blackholes

    this passage is from Paul Davies' the Last Three Minutes: I have a very difficult time believing and understanding this. Why would two quarks being in close proximity create a black hole? A nucleus is only 3 orders of magnitude larger than a quark which i like mount everest compared to a...
  20. R

    Can Stars Become Black Holes Without Going Supernova?

    I have a question about the formation of black holes. Correct me if I am wrong but as I understand it, if you have a massive enough star that when its used up all its fuel and collapses, it will overcome the exclusion principle and crush itself into a black hole. My question is, during this...
  21. S

    What would happen when Blackholes Collide?

    What would happen to the spacetime fabric when two super massive black holes collide. I know that they would orbit each other and the would produce gravitational waves.
  22. L

    Do All Black Holes Exhibit Rotation?

    There are two representations of black holes that I see in the popular media. Could you help me find the answer to a (or two) question about this please? 1. Feeding black hole with an accretion disk - I assume that the accretion disk is a product / consequence of rotation (in addition to the...
  23. G

    Do Minute Black Holes Appear and Disappear in Empty Space?

    I read in an article (lecture) by Stephen Hawking that very minute black holes keep on appearing and disappearing in empty space. Would anyone like to explain this?
  24. M

    What does a black hole look like from behind?

    Hi guys, can't find a post similar to this so ill ask; What does a black hole look like from behind? The spatial apperance is similar to a heavy object sitting on a taught towel or sheet (due to its large mass affecting space-time), but what does an observer on the singularity side (further...
  25. B

    Can you create a black hole from light? Also, Whiteholes vs. Blackholes

    I recall reading about creating a black hole from having an area of space-time occupied by a sufficiently high enough number of high-energy photons, so as to create a black hole. I believe this has some German name, but I can't recall it at the moment. Does anybody have an opinion on this...
  26. Evo

    Intellectual blackholes, battling nonsense

    Again, there is a bad word, ignore it. Yes, he appears not to know about the affect of different altitudes/pressures on the boiling point of water, but he's a philosopher, not a scientist. He still makes good points...
  27. M

    Are blackholes formed in other ways besides supernovas?

    In science books I always have read that supper massive black holes explode in a supernova once they run out of fuel. After that the core of the star collapses and forms a black hole. But are there other ways in which black holes are formed in nature, besides the the core of a big star...
  28. T

    Black Holes and Gravity: Answers to Your Questions

    Hello, I've been wondering about a few things, I hope you can answer my questions. Question A. If you look at a black hole that has something behind it, say a nebula in our example, what does the black hole look like? Would it be a completely black spot in the middle of the nebula...
  29. S

    Are Black Holes Infinite and Do They Emit Jets?

    From what I understand a black hole is the result of a tremendous amount of matter being pulled together to a finite point in space and this point creates some kinds of a dip in space. Please correct me if I am wrong? Questions.. How big can a black hole get? I've heard something about...
  30. J

    Entangled Particles and Black Holes: A Conundrum of Observation?

    I was watching a show on TV about physics and a question popped into my head that I can't find an answer to. I remember hearing it may be possible to create tiny black holes in the LHC, so maybe you can test this, I don't know. Here is my question... What would happen if you took two entangled...
  31. T

    Do Falling Observers Experience Blueshift Inside a Black Hole?

    If you could safely stand inside a black hole about the size of a small room, filled it with smoke, and shined a laser - would you see the light not only bend towards the warping gravitational field but also blueshift? My previous post was removed so if you responded I didn't get it. I guess...
  32. L

    Black Hole Diagram: Parts, Types & More

    Im trying to come up with a sort of diagram you could call it, of a black hole and all its "parts" for example i know there's the event horizon, ergosphere, the jets that come out of the poles. And any other helpful info. about black holes and there classification, like there's rotating ones...
  33. G

    Are Black Holes Destroying Our Galaxy? The Truth About Galaxies and Black Holes

    I'm sure this is a stupid and/or already asked question. But I don't do astronomy. If every galaxy has a black hole, and black holes suck everything in, does this mean that our galaxy is being slowly destroyed by black holes? (Everything just keeps getting sucked in) And if so, are we going to...
  34. C

    Exploring Supermassive Black Holes: Understanding Orbiting Stars and Gravity

    Hello, I was watching a show on one of DirectTV's Science channels last night about supermassive black holes. They stated the these supermassive black holes exist in two phases : 1. When they are sucking in everything around them (stars, planets, moons, etc). 2. When they aren't sucking in...
  35. A

    Light & Black Holes: Can Massless Light be Sucked?

    Hello, I have a question, since light has no mass how can it be sucked by a black hole, doesn't anything with no mass have zero weight (W=mg), or are photons somehow attracted to black holes?
  36. E

    Blackholes In The Early Universe

    Would it not be possible for many black holes to form in the beginning stages of the universe since the universe was very dense? Can that be the cause of the so called "Dark Energy" or "Dark Matter"?
  37. J

    God & Blackholes: Mysterious Ways vs Physics Theories

    "God works on mysterious ways, which we don't understand" - a usual answer I hear from theists when asked about some contradictions. As per the current Physics, "Inside a black hole, every existing physics theory breaks." What's the difference between these two statements? Does god...
  38. A

    Energy, blackholes and whiteholes

    if a black hole absorbs mass and makes it disappear from this universe. Where is the missing energy from that mass in the universe, considering that the total energy is a constant. Could it be white holes the answer?
  39. X

    Finite Black Holes? Answers for Xap's Question

    please forgive my ignorance but, i was watching somthing in tv the other day about supermasive black holes, now my question is, if some black holes are more massive than others, how can their mass be infinite? if Blackhole A is more massive than black hole B then surly they can't both be...
  40. A

    Hey guys, this is my theory of blackholes and how new parallel universes

    my theory of black holes, and the start of the universe, ok ,all black holes go to central point of mass, all the central points of all the black holes combine to converge to a parallel universe, which takes the mass from our universe, to start the "big bang", when enough mass has been forced...
  41. R

    Does Time Slow Down in a Black Hole?

    It is stated that nothing can escape a black hole and they are gigantic and powerful enough to rotate a galaxy. The gravitational force of space acting on the black hole is immense. On this level of gravity could time it self be stopped in the black hole? Therefore the amount of mass taken by...
  42. J

    Blackholes and 2nd Law of Thermodynamics

    Is it possible to deduce that a black hole must have something akin to Hawking radiation due to the 2nd Law of Thermodynamics? Let us consider for now a purely classical black hole. The event horizon is effectively a 'light diode' in that if light can pass through in a particular direction...
  43. J

    What distinguishes Kerr and Schwarzschild blackholes?

    Consider the Schwarzschild black hole vacuum solution. Now let a test particle drop from "coordinate rest" at a finite r, and watch it fall in. Is there a coordinate transformation in which we go to a rotating frame where the black hole is now a Kerr black hole and the test particle follows...
  44. M

    Explaining blackholes dark matter ?

    Ok so i don't know squat about either subject, so blame Nova for this post. The show was talking about reaching absolute zero and einstine's conensate theory. As they talked about using intense magnetic fields and shot light waves through these near zero gas clouds causing light to slow. one...
  45. F

    Singularity in reference to blackholes and right before the big bang?

    Now correct me if I'm wrong. Gravitational singularity is when It has a defined mass but no volume and the equation for density is d=m/v. If a black hole's mass is say 10^40 yottagrams and its a singularity so it has no volume = 0. How can it have infinite density if the equation is (10^40...
  46. G

    Could a Supermassive Black Hole Destroy Our Galaxy?

    So, according to stuff i have read over the past few days (quite interesting stuff out there) there is a "supermassive black hole" at the center of our universe. what i would actually like to know is if this had the supposed mass it does which if i am correct with my memory was something along...
  47. J

    String Theory: Higgs and Blackholes

    First question: Since a neutral Higgs boson is its own anti-particle, and has zero spin, it appears to have zero for all quantum numbers (in the standard model). This is what one would expect as well for the smallest neutral black hole with no angular momentum. What "new" quantum numbers...
  48. B

    Blackholes, Jets and Dark Matter.

    this topic relates to my post in a threat relating to GLAST https://www.physicsforums.com/showthread.php?t=240620 Super massive black holes eject jets of matter back out into space. The matter in these jets shoot out of the black hole at 99% the speed of light. However the escape velocity...
  49. B

    Simulating globular clusters over blackholes with Fortran

    I suspect that the runtime simulation for a star systems containing thousands of stars , many of those stars whose mass is way beyond the solar mass to be very very long. Is it possible and cost-friendly(i.e, not expensive) to simulate a globular star system cluster over a supermassive black...
  50. K

    Micro Blackholes: Quantum Level & String Theory

    What are miniature black holes at a quantum level? What does string theory say?