New answers tagged black-hole
3
Hawking is referring to the Black hole information paradox.
In classical theories (such as Newtonian mechanics and General Relativity) the model is deterministic. If you know the precise initial conditions of a physical system you can predict its future evolution.
Quantum mechanics introduces indeterminacy: When a quantum system is observed, there is a ...
2
If you don't consider how the black hole has formed, then it is quite possible for a black hole to form a bound state with a massive object like a star. If the star has a much higher mass than the star, both can circle (or ellipse) around their center of mass. If this COM lies close to the star then the BH will be orbiting around the star. There will be no ...
8
This is a great series of questions!
Such a low mass black hole (BH) could have originated from a few possibilites: 1) a result of stellar evolution (the resulting black hole mass depends fundamentally on the initial mass and metallicity of the stellar progenitor, among other things); 2) a star collapsed into a neutron star which can accrete matter from its ...
9
A black hole of a given mass will probably have arisen from the collapse/supernova of a much more massive star. In particular, stars with an initial mass of less than around 15-20 solar masses are unlikely to leave a black hole remnant at all. Stars of $<8$ solar masses end their lives as white dwarfs and those with $8$ to $\sim 15$ solar masses likely ...
3
One of the results about black holes in classical General Relativity is the "No Hair Theorem". This says that black holes have exactly 3 properties:
Mass
Angular momentum
Electric charge
All other properties of the matter that falls into a black hole is lost.
Now black holes can change these properties. As matter falls into the black hole, its ...
4
It depends on the context, since "age" is not a trivial concept for nonliving entities. If you're interested in the connections between stellar evolution and black hole evolution, then you might consider the black hole as the last stage of development in a (high mass) star's life. Or if you're considering black holes forming in dense stellar ...
1
His theory says that the sum of all energies is equal to zero. Positive energy in the form of matter is exactly cancelled out by negative energy in the form of gravitational energy. More on the Wikipedia page about so called zero-energy universe. It is worth noting that his theory is supported by two observations in 1998, but many perceive it as some sort of ...
-2
You can even consider our visible universe to be a black hole. As there are stars around us, they can live quite undisturbed in it. As seen from the part outside the horizon our region is the black hole. Stars from the other side seem to move onto our region but will be seen to end at the horizon (just as we see matter move onto their region, so seen from us ...
28
In order to survive, the star's self-gravitation must be larger than the tidal stretching forces provided by the black hole. If not, then the star will get spaghettified before it crosses the event horizon.
The tidal acceleration on a freely-falling star at the event horizon of a (non-spinning) supermassive black hole is approximately
$$g_{\rm tidal}\simeq 2\...
2
As a fairly close analogy for what happens with Schwarzschild coordinates, suppose you replace Cartesian $(x,y)$ coordinates for the Euclidean plane with $(x,z)$, where $z=y/x$.
There is a bijection between these coordinate systems for all points with $x\ne 0$, but the points with $x=0, y\ne 0$ are not covered by $(x,z)$ coordinates at all, while the origin ...
0
I am doing a research on central SMBH-galaxy mass relation. Through my research, I came across many papers on observations of this relation. Almost all of them had a mass range of $~10^{10}M_\odot to ~10^{13}M_\odot$ as the DM halo mass. Whereas the SMBH mass was in range of $~10^{6}M_\odot to ~10^{11}M_\odot$ in the local universe.
Here are some points to ...
0
A black hole does not necessarily suck in everything around it. Something that is outside $r = 2GM/ c^2$ radial distance (Schwarzschild radius) from the black hole, behaves in a similar way as if the black hole were a normal gravitating object.
Here is a Schwarzschild radius calculator online
For a mass equal to that of the earth, the Schwarzschild radius is ...
2
I will try to generalize your question to 'why does any object not become a black hole?'. It is indeed true that the center of mass of an object pulls the mass around it, so why does it not collapse?
We need to see, what force is balancing the force of gravity. If you press an object (let's say: Iron), as hard as you can, why does it not get destroyed ...
0
... but how does the other know how to take energy from the black hole?
In order to understand this, you need to be familiar with the essence of this picture$^1$ including negative energy states inside the horizon, creation of virtual particle-antiparticle pairs, and conservation of energy.$^2$ I try to intuitively answer your question with simple words.
...
1
tl;dr: A study reported a possible scale (in)variance of a tidal disruption event or TDE.
Axios' Big and little black holes feed the same way has their own recent take on this question.
What they found: The study (Rapid accretion state transitions following the tidal disruption event AT2018fyk) in the Astrophysical Journal suggests all black holes go ...
2
If you have a spherical ball of matter, then outside that ball of matter, the gravitational field is the same as if all them mass were concentrated at a point (as a black hole)
But inside the ball of matter, some of the mass of the ball is behind you and acts in the opposite direction. This means that the gravitational field is at a maximum on the surface ...
4
Because you are somewhat larger than your Schwarzchild radius.
In order to turn into a black hole and start experiencing exciting things like Hawking radiation, you'd need to be compressed down into a ball about $10^{-25}$ meters in diameter, about one ten-billionth the size of a single proton. At that size, you'd have a hard time sucking anything in: your ...
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