Black Holes?

[mikey32shaw]

I'm sure this may have been explained so if so please forgive me. After watching The Sky At Night this evening there main topic was black holes. I was wanting to know if someone far more intelligent than me could answer a few questions?

1, As far as I was aware a black hole was a collapsed star many masses larger than our sun. These black holes allow nothing to escape upon passing the event horizon. Is all of this true?

2, The main belief is that nothing can travel faster than the speed of light. And once inside a black hole nothing can escape not even light?

3, now this is the main question there now saying they are observing massive steams of gasses being ejected from the centre of some black holes how is this possible? I thought nothing could escape not even light? And if these gases are escaping are they travelling faster than the speed of light?

I'm sure there are explanations to the above bit was hoping someone could shed a little light on it for me

Thanks in advance

Mike

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[mikey32shaw]

I'm sure this may have been explained so if so please forgive me. After watching The Sky At Night this evening there main topic was black holes. I was wanting to know if someone far more intelligent than me could answer a few questions?

1, As far as I was aware a black hole was a collapsed star many masses larger than our sun. These black holes allow nothing to escape upon passing the event horizon. Is all of this true?

2, The main belief is that nothing can travel faster than the speed of light. And once inside a black hole nothing can escape not even light?

3, now this is the main question there now saying they are observing massive steams of gasses being ejected from the centre of some black holes how is this possible? I thought nothing could escape not even light? And if these gases are escaping are they travelling faster than the speed of light?

I'm sure there are explanations to the above bit was hoping someone could shed a little light on it for me

Thanks in advance

Mike

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[heedthebaw]

Watched a video on youtube that I found quite interesting. All about black holes and how some rather clever people tracked down their location at the centre of galaxies!

Goes onto explain about the phenomenon you've described in part 3 but i'm far too lazy to try and post an explanation so i'll let you watch

[JulianO]

I'm sure this may have been explained so if so please forgive me. After watching The Sky At Night this evening there main topic was black holes. I was wanting to know if someone far more intelligent than me could answer a few questions?

Its not intelligence thats needed - just knowledge!

1, As far as I was aware a black hole was a collapsed star many masses larger than our sun. These black holes allow nothing to escape upon passing the event horizon. Is all of this true?

Yes - thats correct. There mass means the escape velocity due to gravity is greater than the speed of light. A mass bigger than about 3 or so solar masses will cause a black hole - but stars lose a lot of mass in their final days, so in practice it needs to be about 8 solar masses before it goes off.

2, The main belief is that nothing can travel faster than the speed of light. And once inside a black hole nothing can escape not even light?

True - Einsteins equations state the universes speed limit is that of light. Nothing can go faster - including CERNs neutrinos

3, now this is the main question there now saying they are observing massive steams of gasses being ejected from the centre of some black holes how is this possible? I thought nothing could escape not even light? And if these gases are escaping are they travelling faster than the speed of light?

The gases are ejected from the accretion disk, this is a area around the black hole where gravity is not yet enough to make the escape velocity > than the speed of light. So this material hasn't got into the black hole, but is losing a lot of energy as it falls in. Lots of other processes including friction and huge magnetic fields which funnel some of the very hot ionised gas out into space.

Once the stuff goes over the event horizon, it's gone though, never to return!

Hope that helps

[ronin]

When they said: "they are observing massive steams of gasses being ejected from the centre of some black holes".

I suspect they meant: "they are observing massive steams of gasses as if being ejected from the centre of some black holes"

The jets will be from outside the event horizon, but the stream appears to originate from the centre. I would guess it is ejected along the axis of rotation of the black hole.

They probably never expected anyone to think too deep about what they said.

email Dan and ask him. :grin:

[mikey32shaw]

^^^^^ That explained it very well, I feel much more confident about being able to explain this to my Dad who was also asking the same questions. I won't take the credit for it though ;-)

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[ScottS]

Quasars!

[FraserClarke]

1, As far as I was aware a black hole was a collapsed star many masses larger than our sun.

That is true for "small" black holes, made from big stars. These have masses of about 10 times that of the Sun.

There is another class of black holes found at the centre of most (all?) galaxies, which are much much bigger; a million times the mass of the Sun, or more. These form in a different, and as yet not very well understood, way. These are the black holes which power quasars.

[pippolotta]

What about the Heisenberg principle (http://en.wikipedia.org/wiki/Uncertainty_principle)? I'm not an expert, but if you know the velocity of a certain particular, you can't know its exact position. Therefore, a black hole cant be black... ask Stephen H. ;-)

[JulianO]

What about the Heisenberg principle (http://en.wikipedia....ainty_principle)? I'm not an expert, but if you know the velocity of a certain particular, you can't know its exact position. Therefore, a black hole cant be black... ask Stephen H. ;-)

This only applies on very tiny scales. Black holes aren't technically black either, due to Hawking radiation. However for typical large black holes this is a fairly small effect, so they still look black close up. The accretion disk if they have one is very bright however - in nearly all wavelengths.