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Phy_enthusiast
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is black hole a theoretical concept or a natural phenomenon?
You are writing as if this was an either/or question. It's not. The answer is "yes".Phy_enthusiast said:is black hole a theoretical concept or a natural phenomenon?
D H said:You are writing as if this was an either/or question. It's not. The answer is "yes".
D H said:You are writing as if this was an either/or question. It's not. The answer is "yes".
D H said:You are writing as if this was an either/or question. It's not. The answer is "yes".
I think it is fair to call a region enclosed by an event horizon a "black hole". Even if all of it's mass appears on it surface.mrspeedybob said:The existence of black holes is kind of a philosophical question since time dilation prevents the event horizon from existing until you actually fall in. Black holes do not actually exist in our frame of reference. The celestial objects we call black holes are really frozen by time dilation right on the verge of becoming black holes (I think of them as very very dim holes). Never-the-less we could, in principle, go to one of these objects and fall behind an event horizon. So, whether the thing actually exists depends on exactly what definition of existence you choose.
Phy_enthusiast said:I wrote like that because theoretical physics is understood by very few.Does anyone know a verified black hole in the sky{experimentally}
mfb said:
Well, there are massive, very small objects which do not emit (significant) light on their own. That is certain.atyy said:But the article says "black hole candidates", and as of 2009 these authors http://arxiv.org/abs/0903.0100 wrote "Are the massive dark central objects in galaxies really Kerr black holes?", and considered "If the central object is not a black hole, but rather a boson star or something similar, then the inspiraling object will continue to emit long after it would shut off in Kerr (Kesden et al. 2005). This would be a clean and blindingly simple falsification of the central black hole paradigm." Kesden et al http://arxiv.org/abs/astro-ph/0411478 also write "the “smoking-gun” signature of an event horizon has yet to be observed. Until such a definitive determination is made, other candidates such as boson stars should continue to be considered."
mfb said:Well, there are massive, very small objects which do not emit (significant) light on their own. That is certain.
X-ray spectra of accretion disks have been measured, and the inner edges of those (determined by the redshift) are consistent with the predictions for the smallest stable orbit around black holes. This means the massive, very small object has to be smaller than a few times the Schwarzschild radius. And it has to be dark.
http://www.black-hole.eu/index.php/general-public/p5-constraining-strong-gravity-using-iron-line-features-in-black-holes
A strong and broad iron line in the XMM-Newton spectrum of the new X-ray transient and black-hole candidate XTE J1652-453
The precise metric of rotating black holes is a different question.
The authors write that it is important to test the predictions of GR (it is always important to test existing theories), but they don't think that GR is wrong.
No we haven't seen one yet, but they're believed to exist.Phy_enthusiast said:So there is no perfect example of a black hole yet?
I agree with this. All so-called black holes, I think, must be called quasi-black holes. Furthermore, if a black hole is formed from a chunk of dust, I think, time dilation also prevents the dust from falling further before becoming a genuine black hole because time dilation is larger at the central region than at the surface. It must be observed as frozen in the air. As a result, singular point will never be formed. Following link shows further discussion.mrspeedybob said:time dilation prevents the event horizon from existing until you actually fall in. Black holes do not actually exist in our frame of reference. The celestial objects we call black holes are really frozen by time dilation right on the verge of becoming black holes
A black hole is both a theoretical concept and a natural phenomenon. It is a concept in the field of physics that describes a region of space where the gravitational pull is so strong that nothing, including light, can escape from it. However, there is strong evidence from observations and mathematical models that suggest black holes exist in the universe.
Black holes are formed when a massive star dies and its core collapses under its own gravity. This collapse causes the star to become extremely dense and compact, resulting in a singularity, a point of infinite density and zero volume. This singularity is surrounded by a region called the event horizon, which marks the point of no return for anything that gets too close to the black hole.
Black holes themselves cannot be seen because they do not emit any light. However, the effects of a black hole can be observed, such as its gravitational pull on surrounding matter and its distortion of light. Scientists use this evidence to infer the presence of a black hole.
According to current theories, black holes do not last forever. They slowly evaporate over time due to a process called Hawking radiation, named after physicist Stephen Hawking. However, this process is extremely slow, and it would take trillions of years for a black hole to completely evaporate.
Once something crosses the event horizon and enters a black hole, it cannot escape. This is because the escape velocity of a black hole is greater than the speed of light. However, things can orbit around a black hole without crossing the event horizon, and some particles may be ejected from the black hole through Hawking radiation.