# Tag Info

### Wouldn't Miller's planet be fried by blueshifted radiation?

For a 2.7 K blackbody (like the CMB) the calculator at http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/radfrac.html gives me 3 $\mu$W/m$^2$. This is how much Earth is heated by the CMB — not a lot! ...
Accepted

### Wouldn't Miller's planet be fried by blueshifted radiation?

Miller's world would be fried by a strong flux of extreme ultraviolet (EUV) radiation. The cosmic microwave background (CMB) would be blueshifted by gravitational time dilation and then would be very ...
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### Why would black hole rip me apart?

The tidal force between your head and feet depend on the difference in $GMm/r^2$ for the two different r values, one about 2 metres closer than the other. Tidal ...
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### Could we be sucked up entirely by a micro black hole?

If you and the black hole were the only things in the universe, then you would just be tidally shredded and then consumed extremely rapidly for a black hole of any sensible macroscopic mass. Anything ...
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### Why we don't see time dilation in stars orbiting black hole?

We do "see it" but the effect is smaller than you imagine. As already pointed out, the effects of time dilation are too small to have any visible apparent influence on the orbits in that ...
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### Why would black hole rip me apart?

There are nice answers by @fraxinus and @profrob, I would like to add a little side note about the balance between the forces. It arises because the gravitational field exerted on one body by another ...
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### Why would black hole rip me apart?

The inertial frame that falls towards the mass freely is only approximately an inertial frame. Around the Earth the approximation is almost perfect agreement. In the ISS, if you place marbles ...
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### Why would black hole rip me apart?

As a complement to the other answers: Not every black hole is capable of ripping you apart tidally. Too small black hole will burn and blow you away you with its Hawking radiation way before you are ...
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### Does an observer experience stronger gravity on the way towards the singularity?

Time dilation is said to be already infinite at the event horizon, so how could it become stronger inside? Yes but that's seen from the outside. When you fall in you don't experience local time ...
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### Are there any other significant radii around Schwarzschild black holes besides the four I know of?

There are radii that play a role when a black hole is observed from afar, for example by the Event Horizon Telescope. For example, the event horizon appears to be $2.6r_s$ because the space around the ...

### Why would black hole rip me apart?

It's also worth nothing that in the case of many black holes of which we have knowledge, the radiation from the accretion disk is so intense that you would be blasted into plasma long before you ...
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### Does an observer experience stronger gravity on the way towards the singularity?

One of the great differences between classical and relativistic gravity is that in the former there is no side effect in supposing all matter concentrated at a point (well, except for the huge tidal ...
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### Why would black hole rip me apart?

The problem is that when you are falling, all of you can't be in the same inertial frame. That is, whilst your centre of mass might be inertial, parts of your body will be feeling accelerating forces ...
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### Does an observer experience stronger gravity on the way towards the singularity?

The implication of your comparison with a neutron star is that you define "gravity" as the force required to keep an object at fixed radial coordinate. By this definition, the "gravity&...
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### Does an observer experience stronger gravity on the way towards the singularity?

A black hole is a singularity in space; there is no going inside (defined as being surrounded by black hole matter). Rather, you could only get closer and closer to the singularity. When you get ...
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### How fast would a clock falling into a blackhole tick relative to the reflection of a clock stationed far away?

If you drop it from rest at radial coordinate $\rm r=r_0$ the free fall velocity at $\rm r=r_1$ is $$\rm v=c \ \sqrt{\frac{r_s \ (r_0-r_1)}{r_1 \ (r_0-r_s)}}$$ which in the limit of $\rm r_0=\infty$ ...
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### Where does all the energy in black holes go?

The short answer is: To the future! EDIT: reading OP's question again, they seem to point out, that the temperature of inbound particles is measured by a distant observer as being near zero. But since ...

### Where does all the energy in black holes go?

Firstly I answer question: "How can a very cool object have a large amount of thermal energy": By having a large heat capacity, by having a large number of internal states, by for example ...
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### Self-coupling of gravity and gravitation escaping a black hole - contradiction?

"Self-coupling" means that yes, gravity gravitates -- that for example gravitational waves would be affected by the gravitational field of objects they move past. Gravitons, if they exist, ...
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### Where does all the energy in black holes go?

Energy inside black holes doesn't "go" anywhere. Energy and mass are the same thing ($E=mc^2$). There's a "no hair" theorem that says that black holes can be completely described ...
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### Is it possible the Black Holes to be pure deformations in the fabric of spacetime and not an effect of super-dense matter?

Your explanation in your comment: My definition is the absence of spacetime or vacuum space inside the event horizon will not work. If this were correct then the whole event horizon would be a ...
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### Is it possible the Black Holes to be pure deformations in the fabric of spacetime and not an effect of super-dense matter?

Is there any theory in the literature that supports this hypothesis that BHs in their center do not have a super dense matter singularity but are pure deformations in the fabric of spacetime itself or ...

### Why are there three bright spots in the first picture of Sagittarius A*?

Imaging artifacts This image is created by complex image reconstruction algorithms that propose alternative solutions which are averaged. Some of these alternatives do not show a ring structure but ...
1 vote

### What does a black hole accretion disk look like edge on?

You would still see a ring, but it would be quite asymmetric in brightness. The ring is not wholly a direct image of the accretion disk. It includes light from all around the black hole that has been ...
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Accepted

### Smooth vs analytic spacetimes

We only impose $C^{\infty}$ when setting up the general theory, because real-analyticity would be too strong a condition to impose. However, when trying to find specific solutions (Schwarzschild, ...
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### About the non-intuitive announcement at 12 May 2022 of the EHT team that spin axis of Sgr A* Black Hole facing Earth?

This recent Nature publication seems to contradict the EHT claim in their presentation about the orientation of the Sgr*A BH accretion disc plane relative to the Galactic plane. Seems to me that gas ...
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### About the non-intuitive announcement at 12 May 2022 of the EHT team that spin axis of Sgr A* Black Hole facing Earth?

I think what you mean is that the spin axis of the black hole is not aligned with spin axis of the Milky Way? NB: That's about all you can say - the conclusion of the actual science paper (Akiyama et ...
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1 vote

### Why are we so sure that there is a singularity inside the event horizon of a black hole?

how can we be certain that there is a singularity at the centre You are starting from a Schrwazchild black hole model which is an idealized eternal model and so never changes. This is a useful basic ...

### Why are we so sure that there is a singularity inside the event horizon of a black hole?

I was just 3 minutes ago reading Planck Stars by Carlo Rovelli. In it he conjectures that a star does not collapse down to a singularity, but rather it collapses down to Planck density: 10^93 g/cm^3 ...
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Accepted

### I'm confused about the number of Killing vectors in Schwarzschild metric

A brute force (and ugly) derivation of the Killing fields of Schwarzschild metric The Schwarzschild metric is ds^2 = -\left(1-\frac{R_{\text{S}}}{r}\right) \text{d} t^2 + \left(1-\...
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