# Tag Info

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The emissions we observe from quasars and blazars are not coming from the black hole, but from the accretion disk that surrounds it. The linked Wikipedia article to quasars even says (emphasis mine), Quasars are believed to be powered by accretion of material into supermassive black holes in the nuclei of distant galaxies, making these luminous versions ...

5

Understandably, Einstein would probably have been uncomfortable with the idea of singularities being consequences of GR. Your quote seems to indicate that he thought the singularity of a Schwarzschild solution was an accident caused by exact spherically symmetry, and that a more generic configuration would somehow not result in a singularity at all. However, ...

5

If you stick to the theory of general relativity then what happens to the matter is fairly straightforward. As the matter falls inwards it experiences increasing tidal forces. The matter reaches the singularity in a finite (short!) time, and at the singularity it is compressed into a point with zero size and infinite density. Note that nothing special is ...

4

No, it is not a possibility. I don't say this to cast doubt on the existence of micro black holes, but rather because of their properties. Black holes evaporate via a process known as Hawking radiation. This means that, in theory, every black hole should eventually evaporate completely, and disappear. For micro black holes, this would be very important. Any ...

3

Although there are suggestions that a black hole could lead into another expanding universe you should regard these as highly speculative. Although the metrics can be stitched together it requires a contribution from currently hypothetical quantum gravity effects. Until we have a working theory of quantum gravity there is no way to comment on how likely the ...

3

No. You must have made an error in determining the GR horizon radius. The radius of the event horizon determined from Newtonian theory (simply determining the distance from a point mass at which the escape velocity equals the speed of light) happens to be the same as the radius rigorously derived from the General Relativistic equations. This, by the way, ...

3

Only static spacetimes are derivable from a potential. Spacetimes for rotating black holes aren't static, so they can't be derived from a potential. The spacetimes for nonrotating black holes are static, so they can be derived from potentials. Since the spacetimes are different for black holes with different amounts of charge, it follows that the ...

3

If we take the Milky Way as an example, the black hole at the centre, Sagittarius A$^*$, has a mass of about 4 million times the Sun. However the mass of the Milky Way is somewhere around a trillion Suns. So the central black hole makes up 0.0004% of the total mass. While the central black hole may have been important in the formation of the Milky Way, its ...

3

Comment to the question (v1): Besides what John Rennie wrote in his correct answer, note that the velocity profile of an irrotational/free vortex falls off as $$\tag{1} v~\propto~ 1/r,$$ while a galactic rotation curve may actually increase with $r$, and in any case, it never falls off faster than$^1$ $$\tag{2} v~\propto ~1/\sqrt{r},$$ so the analogy ...

3

Direct experimental evidence of Hawking radiation is going to be exceedingly difficult to obtain. The radiation from stellar mass black holes is so small as to be undetectable, and we haven't (yet) worked out how to small black holes in the lab. At the moment there is no direct experimental evidence, and we have to accept we may not see any in our lifetimes. ...

2

Here's an answer from a nonspecialist who's reasonably comfortable up till the end and no further of "The Big Black Book" (Misner Thorne and Wheeler) and with a general lay reading other than this. Although often asked and thought about a great deal by physicists, your question is an excellent one because it leads straight to the edge of our knowledge of ...

2

This is actually more subtle than you would think it would be. First, remember that a fourier transform is defined, for some time-dependent signal $F(t)$, as${}^{1}$: $$F(\omega) = \frac{1}{\sqrt{2\pi}}\int_{-\infty}^{+\infty} dt\, e^{i\omega\,t} F(t)$$ Well, this is great in special relativity, but in general relativity, what time do we actually use? ...

2

If you're not up to speed with general relativity this is going to be hard to explain, but I'll give it a go. The more determined reader may want to look at this PDF (just under 1MB in size) that describes the collapse in a rigorous way. A couple of points to make before we start: you're being vague about the distinction between the singularity and the ...

1

Let us try to clear up terminology here: A black body is classically defined as a perfect absorber of radiation. No, it is not. The classical description of the perfect absorber also includes an emitter black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. A ...

1

The scenario you are talking about may have taken place as a sort of a "Big bounce". Big bounce is the theory of a cyclic universe implying that the big bang in the past will be followed by a big crunch in the future, followed again by a new big bang and so on. However, currently a future big crunch is considered as less probable because it seems that ...

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My answer to your question is an absolute "no". First of all Black holes do not implode, that would suggest them blowing up in some way, they can grow but to say implode is null.

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There is plenty of evidence for the underlying quantum field theoretical description of the vacuum. The (complete) quark content of the nucleons has been measured, and includes both flavors not in the valence content (strange, charm (?)) and lots of anti-quarks. Everything that isn't valence content ($uud$ for a proton or $udd$ for a neutron) is called the ...

1

If the event horizon is really a one-way surface, the answer is that whatever happens inside the event horizon is irrelevant to our universe. An object that crosses the event horizon will appear to an outside observer to take an infinite amount of time to do so, and no model of the interior of a black hole can ever be tested. Whether the event horizon is ...

1

This answer expands on @Rex s answer, on the part elementary particles have in a black hole creation. It is often said that when the gravitational force exceeds any outward forces or pressures, mainly the electron degeneracy pressure I'm thinking, the star collapses into a black hole. But how can this happen without the Pauli exclusion principle being ...

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