New answers tagged

1

This is indeed possible! With a risk of overstatement, this fact is extremely important for astrophysics because it turns out that by dipping in and out of the ergogregion (the region between the surface of infinite redshift and the event horizon) one may extract quite a bit of energy and angular momentum from a rotating black hole in a process known as the ...


1

Traversable - Overlapping (actually intersecting) region would not be Traversable even if the gravity at some parts of the region may be zero. For exampple, between earth and moon, gravity will be zero at some point. That does not mean something in that region can go out of earth/moon system. As soon as an observer leaves that region, it either falls towards ...


8

The most distant object that light we emit today can reach in the distant future is at the event horizon $$eH(t) = a(t)\cdot \int_{t}^{t_{max}} \frac{c\cdot \text{d}t'}{a(t')}$$ which is now approximately 17 billion lightyears away, see the future light cone in comoving coordinates which converges to this distance: If the light was emitted at the big ...


0

If the event horizons overlap you get one big horizon. EM forces can not counteract gravity if the curvature is too large since the force required to counteract gravity becomes infinite at the horizon. You can see this in the equation $$F=\frac{G\cdot M\cdot m}{r^2\cdot\sqrt{1-r_s/r}} $$ which becomes infinite at the horizon $r_s$. Since from the outside ...


1

The metric for the de Sitter spacetime, which approximates the observable universe in stationary coordinates is $$ ds^2~=~-\left(1~-~\frac{r^2\Lambda}{3}\right)dt^2~+~\left(1~-~\frac{r^2\Lambda}{3}\right)^{-1}dr^2~+~r^2d\Omega^2 $$ The important term is $$ \left(1~-~\frac{r^2\Lambda}{3}\right), $$ that looks a bit like the Schwarzschild factor. This ...


0

Well first of all, Considering dark energy and other factors, what is the most distant object light could reach? If you are talking about an OBJECT like stars, galaxies etc... the farthest object we can "see" is located 13.39 bilions light-years (Galaxy GNz-11, you can search that) The 11 on the name indicates its redshift z=11. ...


0

A first problem is that there is in GR no such thing as "an observers frame", except in sloppy speech. There are various systems of coordinates. Two systems of coordinates may agree for an observer as much as one likes but differ elsewhere. And all the systems of coordinates are on equal foot, none is preferred. What could replace the "observer's frame"? ...


4

The "theory" describing the black hole interior (in the classical approximation) is the same theory that implies the existence of the black holes, namely the general theory of relativity. As the OP correctly said, the singularity at the event horizon is a coordinate singularity – one that is an artifact of a bad choice of coordinates. When a coordinate ...


2

Well, plenty of black holes show jets of highly energetic gas or plasma coming out perpendicular to their rotation plane, seemingly out of the hole. It's just accreting highly energetic gas that's spiraling into the black hole but can not make it in, much of it does but much of it is expelled out. It is not from the hole, just the energetics works out that ...


2

That's just a very poorly written article. Nothing was observed to exit from inside the event horizon. There was a high energy event that launched a flare from near the BH. The event is unexplained, but doesn't obviously violate any known laws of physics.


0

Yes the singularity of a black hole would be incredibly bright once you get to the center because the light and energy can't escape the black so it is all compressed into and infinity dense small point and even if it is just normal matter going inside the black hole it would even make it more bright because the black hole tidal forces would rip the atoms ...


2

Hawking, I believe, is referring to a more metaphorical 'hovering'. As light, or anything, approaches the event horizon, it becomes more and more redshifted---it's motion appearing to go slower and slower and slower, approaching zero apparent velocity to an outside observer (approximately) infinitely far away. Anything falling into a BH, thus appears to ...



Top 50 recent answers are included