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First real Black Hole image - 10 April 2019


Elendirs
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25 minutes ago, beecee said:

A real shame that Professor Stephen Hawking had not lived long enough to see this momentous event. 

No, but he did get to see LIGO detect gravitational waves!

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11 hours ago, Strange said:

The phrase "event horizon" is a technical term that means there is no causal connection between the inside and the outside. Therefore nothing on the inside can have any effect externally.

Doesn't gravity connect what is inside the event horizon with what is outside?

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2 hours ago, Airbrush said:

Very interesting.  It looks like a glazed donut.  Is the donut hole about the size of the event horizon?

The donut is around 2.6 Schwarzchild radius from what I understand and the info I have read. In other words while the inner most orbit of the accretion disk is at 3 Schwarzchild radii. It is effectively explained here.....https://www.youtube.com/watch?v=zUyH3XhpLTo

Note, the illustration in the video was before this image was released, so it can be seen that the astronomers and scientists were pretty close to the mark of what would be seen.

1 hour ago, Ken Fabian said:

Doesn't gravity connect what is inside the event horizon with what is outside?

The gravity of a BH operates the same as gravity of any massive object, but obviously far more intense. Photons approaching a BH at the appropriate trajectory would orbit at 1.5 Schwarzchild radius, which is known as the photon sphere and is unstable. Nothing of course can ever orbit any closer. The closest edge of the accretion disk is the inner most stable orbit and is at 3 Schwarzchild radius.. This applies to any non spinning BH [for simplicity sake] and its gets far more complicated for any Kerr spinning BH.

Here is a pretty good link maintained by a Professor Andrew Hamilton, that covers most questions etc one would ask about any BH. 

https://jila.colorado.edu/~ajsh/

Edited by beecee
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10 hours ago, Ken Fabian said:

Doesn't gravity connect what is inside the event horizon with what is outside?

Interesting question.

In GR (the main model of black holes) all the mass falls towards the centre. There may be other models where the mass is evenly distributed throughout or distributed at the event horizon (I don't know if there are any such models). These would all be indistinguishable from outside the event horizon (see Newton's Shell Theorem).

When something falls into a black hole (or when they merge) then the event horizon is actually distorted towards the approaching mass. There is then a "ring down" phase where the event horizon oscillates while it settles down into a (slightly larger) sphere again. But that only tells us about the mass that was outside, not what happens when it is inside.

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1 hour ago, Strange said:

When something falls into a black hole (or when they merge) then the event horizon is actually distorted towards the approaching mass. There is then a "ring down" phase where the event horizon oscillates while it settles down into a (slightly larger) sphere again. But that only tells us about the mass that was outside, not what happens when it is inside.

How can an event horizon ring? Isn't time stopped at the event horizon, and thus for an outside observer it should remain unchangeable? I don't even understand how it can grow.

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12 minutes ago, Danijel Gorupec said:

How can an event horizon ring? Isn't time stopped at the event horizon, and thus for an outside observer it should remain unchangeable? I don't even understand how it can grow.

The event horizon is an invariant: it is the same for all observers. And it is not just the event horizon that "rings", it is space-time around it, which is why we can detect gravitational waves.

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11 minutes ago, Danijel Gorupec said:

How can an event horizon ring? Isn't time stopped at the event horizon, and thus for an outside observer it should remain unchangeable? I don't even understand how it can grow.

 

depends on your pov.

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6 hours ago, Danijel Gorupec said:

How can an event horizon ring? Isn't time stopped at the event horizon, and thus for an outside observer it should remain unchangeable? I don't even understand how it can grow.

My take actually says that it is spacetime that is ringing and/or oscilating, analogous to gravitational waves and the Lense Thirring effect. Your last question is best answered imo simply by the fact that all frames of references are as valid as each other.

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2 minutes ago, beecee said:

My take actually says that it is spacetime that is ringing and/or oscilating, analogous to gravitational waves and the Lense Thirring effect. Your last question is best answered imo simply by the fact that all frames of references are as valid as each other.

Spot on. (I thought I had written something to that effect, but apparently that only happened in my head!)

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6 hours ago, Strange said:

Spot on. (I thought I had written something to that effect, but apparently that only happened in my head!)

:D  You did. But I being a lay person, have a better lay person's manner in expressing an idea in lay person's fashion! :P

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On 4/11/2019 at 12:26 AM, koti said:

Heres something to put it all into perspective, there are more Hydrogen atoms in a teaspoon of water than there is tea spoons of water in all Earth's oceans. A Hydrogen atom size is 10^-9 m and the Planck length starts at 10^-34 m:
 

Planck_scale.gif

Since the singluarity is below Planck length territory where the concept of left/right up/down straight/backwords stop to have meaning, the very question if a singularity has volume has no meaning. 

Stupid question: does that mean that in a BH the atomic nucleus is compressed?

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9 minutes ago, michel123456 said:

Stupid question: does that mean that in a BH the atomic nucleus is compressed?

Even in a neutron star atoms and nuclei no longer exist. The particles are compressed to a much denser and more complex state. 

We don’t know what happens in a black hole. According to GR everything is crushed to a point but is probably not realistic. 

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22 hours ago, Strange said:

There is then a "ring down" phase where the event horizon oscillates while it settles down into a (slightly larger) sphere again.

Wouldn't that mean that if enclosed by the event horizon, there are dancing chocolate elephants, we would also notice that because of oscillations of the event horizon?

24 minutes ago, michel123456 said:

Stupid question: does that mean that in a BH the atomic nucleus is compressed?

Just think about the different end stadia of stars. Depending on the mass, there are several possibilities:

  •  (this one nearly does not count) brown dwarfs. Have not enough mass to get hydrogen fusion started, so are compressed till even hydrogen behaves as a metal
  • white dwarfs: End stadium of small to medium sized stars. The compression is stopped by electron degeneracy. According to the Pauli principle no electron can have exactly the same state as another, and this sets a limit to further compression
  • neutron stars: under very high pressure, protons and electrons combine to neutrons. But again Pauli stands at the upper limit of this: as neutrons are fermions just as electrons, no two neutrons can be in exactly the same state
  • black holes: Under even higher pressure the pressure of neutron degeneracy does not suffice, and there is nothing we know of that would stop further compression. And when the object is compressed enough that it is surrounded by an event horizon, we will never be able to investigate, as nothing can leave the inside of a black hole. 

So I think that we are already going too far, if we say that all the mass is compressed in a point, the singularity. That could be the case, but without a quantum theory of gravity, we even have no hint what is inside the event horizon.

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4 minutes ago, Eise said:

Wouldn't that mean that if enclosed by the event horizon, there are dancing chocolate elephants, we would also notice that because of oscillations of the event horizon?

Good question (I did wonder about that myself).

I don't think so. For example, say two objects that were orbiting one another were to fall into a black hole (large enough that tidal forces did not disrupt them much). Before they fall in, they would be generating gravitational waves. Inside the event horizon, the curvature of space-time is such that the only direction for the gravitational waves to travel is towards the singularity. The could not reach the event horizon and certainly not outside it.

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On 4/10/2019 at 12:57 PM, Strange said:

I was just about to post this, which partly answers it:

m87_black_hole_size_comparison.png

From: https://xkcd.com/2135/

It is from the accretion disk. M87 is a fairly active black hole - see the massive polar jets in the second image in that Forbes article.

Does this illustration mean that the size of the event horizon is about 4 times the diameter of the solar system out to Pluto's orbit?

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8 minutes ago, Airbrush said:

Does this illustration mean that the size of the event horizon is about 4 times the diameter of the solar system out to Pluto's orbit?

The radius of the event horizon is about 2x1013 metres. That is about the same as the distance from the Sun to Voyager 1 (which is just outside the Solar System). 

The black area in the image is the "shadow" of the black hole (created by gravitational lensing of the photon sphere) and is 2.6 times the size of the event horizon (see the video poster earlier for a good explanation of that).

Edit: so looking at that diagram again, it would appear that Randall has got the comparison wrong. Which I am rather surprised about.

Edited by Strange
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21 minutes ago, Strange said:

The radius of the event horizon is about 2x1013 metres. That is about the same as the distance from the Sun to Voyager 1 (which is just outside the Solar System). 

The black area in the image is the "shadow" of the black hole (created by gravitational lensing of the photon sphere) and is 2.6 times the size of the event horizon (see the video poster earlier for a good explanation of that).

Edit: so looking at that diagram again, it would appear that Randall has got the comparison wrong. Which I am rather surprised about.

Does that mean that the radius of the event horizon for M87, in our solar system, would extend out to somewhere in the Kuiper Belt, inside the Oort Cloud?

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1 minute ago, Airbrush said:

Does that mean that the radius of the event horizon for M87, in our solar system, would extend out to somewhere in the Kuiper Belt, inside the Oort Cloud?

I make it about twice as far as the Kuiper belt.

This might be useful for comparison purposes: https://en.wikipedia.org/wiki/Orders_of_magnitude_(length)#Astronomical_scale

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