Questions tagged [black-holes]
A black hole is a region of spacetime from which nothing can escape. More formally, the future light cone of any observer within the black hole is completely contained in the black hole, and the black hole region is not within the past light cone of any observer that goes to spatial infinity in an infinite amount of time.
1,110
questions
66
votes
10
answers
10k
views
Do all black holes have a singularity?
If a large star goes supernova, but not enough mass collapses to form a black hole, it often forms a neutron star. My understanding is that this is the densest object that can exist because of the ...
- 5,061
23
votes
2
answers
10k
views
How can Quasars emit anything if they're black holes?
We've heard it many times, nothing can escape the gravity of a black hole, even light once it's past the event horizon. If this is true, how can a black hole emit anything? Quasars are massive black ...
Hunter
20
votes
4
answers
8k
views
How can a singularity in a black hole rotate if it's just a point?
I guess nobody really knows the true nature of black holes, however, based on everything I know about black holes, there is a "singularity" at their center, which has finite mass but is infinitely ...
- 912
16
votes
2
answers
4k
views
Entering a black hole, jumping into another universe---with questions
I'm quite familiar with SR, but I have very limited understanding in GR, singularities, and black holes. My friend, which is well-read and is interested in general physics, said that we can "jump" ...
- 526
10
votes
3
answers
2k
views
How were the solar masses and distance of the GW150914 merger event calculated from the signal?
The GW150914 signal was observed, giving us the frequency and amplitude of the event. Because LIGO has two detectors a rough source location could be derived.
But how do these three factors allow for ...
- 956
26
votes
3
answers
3k
views
So Black Holes Actually Merge! In 1/5th of a Second - How?
I've read a lot of conflicting answers in these forums. However, today saw the awesome announcement of gravitational waves. Two black holes merged: http://www.slate.com/blogs/bad_astronomy/2016/02/11/...
- 401
56
votes
4
answers
13k
views
Does black hole formation contradict the Pauli exclusion principle?
A star's collapse can be halted by the degeneracy pressure of electrons or neutrons due to the Pauli exclusion principle. In extreme relativistic conditions, a star will continue to collapse ...
- 1,917
24
votes
7
answers
4k
views
Given that matter cannot escape a black hole, how did the big bang produce the universe we see today?
Extrapolation of the expansion of the Universe backwards in time using general relativity yields an infinite density and temperature at a finite time in the past.
If the matter contained within our ...
Daniel X Moore
19
votes
3
answers
6k
views
Can we have a black hole without a singularity?
Assuming we have a sufficiently small and massive object such that it's escape velocity is greater than the speed of light, isn't this a black hole? It has an event horizon that light cannot escape, ...
- 677
14
votes
5
answers
3k
views
Questions re significance of 2016 and 2020 LIGO observations
Phys. Rev. Lett. 116, 061102 (2016) - "Observation of Gravitational Waves from a Binary Black Hole Merger"
(https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.061102) reports that ...
- 396
10
votes
5
answers
1k
views
Taking selfies while falling, would you be able to notice a horizon before hitting a singularity?
I am generally interested in the role of "pings"(0a) between participants (a.k.a. "signal roundtrips"(0b), as familiar for instance from Synge's "five point curvature detector") in the determination ...
- 4,296
4
votes
5
answers
2k
views
If you shoot a light beam behind the event horizon of a black hole, what happens to the light?
I have a couple of questions about light here, and sorry of they are silly..
So since anything that goes beyond the event horizon can't go out, so what if a light beam was pointed somewhere behind ...
- 1,137
20
votes
5
answers
37k
views
Why does a black hole have a finite mass?
I mean besides the obvious "it has to have finite mass or it would suck up the universe." A singularity is a dimensionless point in space with infinite density, if I'm not mistaken. If something is ...
- 5,061
14
votes
7
answers
2k
views
Binary Black Hole Solution of General Relativity?
This is rather a technical question for experts in General Relativity. An accessible link would be an accepable answer, although any additional discussion is welcome.
GR has well known solutions ...
- 4,743
12
votes
2
answers
2k
views
Black hole formation as seen by a distant observer [duplicate]
Possible Duplicate:
How can anything ever fall into a black hole as seen from an outside observer?
Is black hole formation observable for a distant observer in finite amount of time? Specifically,...
- 355