[tamsinbell (OP)]

Richard asks:

"We are told that nothing can escape a black hole  - not even light. But Professor Hawking told us that radiation can escape. I do not understand this since light is made from photons which are massless and are the fastest moving objects we are aware of (space itself aside) so how can radiation escape?"

Do you know? Post below...

[evan_au]

Hawking radiation is a theory about what might happen when you combine General Relativity with Quantum Theory near the event horizon of a black hole. For now, it remains a theory which is yet to be proven in practise (and I, for one, am happy that there are no nearby black holes on which to test it...).

There are a number of analogies that are commonly used to explain Hawking radiation, but they all come down to the fact that you can't simultaneously tell the precise energy, position, velocity, energy and momentum of a subatomic particle (or even the precise energy of a vacuum!).

Some of these analogies:
- Exploit uncertainty in the energy of a vacuum to say that perhaps virtual particles can appear in a vacuum (and one gets swallowed by the black hole)
- Exploit uncertainty in the position of a particle to say that perhaps a virtual particle is actually outside the event horizon, while its partner is still inside

General Relativity makes absolute statements like "No object with mass can be accelerated up to the speed of light in a vacuum".
- Quantum Theory is a bit more "forgiving", and allows violations provided they are not too big, and don't persist for too long.
- So when you come to large objects (big enough to be felt by humans), the Quantum effects are almost imperceptible, and General Relativity prevails.
See: https://en.wikipedia.org/wiki/Hawking_radiation

[guest45734]

As Evan_au points out above.

LMGTFY

Also > The accretion disc which exists outside the event horizon of a Black hole emits lots of EM radiation. https://en.wikipedia.org/wiki/Accretion_disk. This radiation is likely what we see emitted from Pulsars
Also > The singularity inside a BH involves infinities, and the laws of nIormal space time do not exist https://en.wikipedia.org/wiki/Gravitational_singularity. This can be interpreted that 4 dimensional space time ceases to exist.
Also> Also a further speculative thing from Einsteins field equations is the existence of an Einstein Rosen bridge a wormhole in space time connecting separate regions of space together. https://en.wikipedia.org/wiki/Wormhole this is none proven however the possibility exists. The wormhole provides a kind of back door to the event horizon which can be regarded as a back door.
Also > Also Quantum Loop Gravity again theoretical not unlike Hawking radiation suggests the Big Bang came from a Black Hole.
Also > To confuse you even further Podolsky theorized our universe exists inside a Black hole.

There is a lot of speculation about what is inside a BH. If you happened to go inside of one, you would not get out intact.    

[evan_au]

The accretion disc which exists outside the event horizon of a Black hole emits lots of EM radiation. ...This radiation is likely what we see emitted from Pulsars

It is true that the plasma of an accretion disk can produce bursty X-Rays that vary on very short timeframes. But these bursts tend to be somewhat erratic.

However, the rock-steady regular pulses from a pulsar are thought to come from the rock-solid crust of a neutron star.
See: https://en.wikipedia.org/wiki/Pulsar

[Richard_656]

Thank you  folks I don't really post on forums but signed up today just to post here, since my question was submitted via an email.

After reading the  above and the Wiki page , it sounds like we need that unified theory pretty soon if we are to truly understand this.  I must admit I do like the big bang being caused by a blackhole theory, the singularity being the point at which it starts ( at least in my mind), trouble is with that is,  from where did the BH come from in the first place (ie - another universe?)  I do hope I live long enough to find out these answers.

Richard

[PmbPhy]

Richard asks:

"We are told that nothing can escape a black hole  - not even light. But Professor Hawking told us that radiation can escape. I do not understand this since light is made from photons which are massless and are the fastest moving objects we are aware of (space itself aside) so how can radiation escape?"

Do you know? Post below...

Radiation cannot escape from within a black hole. virtual particle pairs which appear close to the event horizon will at times absorb one while letting the other escape. That's how radiation and energy escape black holes. But the radiation wasn't inside the blackhole to begin with.

[jeffreyH]

As Pete said above, Hawking radiation occurs outside the event horizon. Virtual particle pairs will normally disappear very quickly. These are not real particles. However, if one of the disturbances is consumed by the black hole the other one does not disappear. It becomes a real particle that adds mass to the universe. It is theorised that this subtracts mass from the black hole. The vacuum remains unchanged, since it can be considered to act like a condensate.

[guest45734]

I forgot to mention yesterday that energy/mass can escape BH's as gravitational waves as was detected by LIGO. If memory serves two BH's orbiting each other emitted gravitational waves. One BH had 29 solar masses and the other 36 solar masses, spiralling into each other to create a single black hole of 62 solar masses. Three solar masses were lost as gravitational waves which rippled through space to us a few years after.

trouble is with that is,  from where did the BH come from in the first place (ie - another universe?)  I do hope I live long enough to find out these answers.

A very good question that only speculative answers exist for. Speculating a little, before any Big Bang Space time did not exist (time and space are expanding due to dark energy). Looking inside a BH space time as we know it does not exist. A theory amongst many others exists developed by Nikodem Poplawski a Russian physicist that the universe we exist in is expanding inside a BH. This as I understand it, is a dimension devoid of space time dimensions, a bit like a worm hole or something of that ilk.

[yor_on]

Define 'escape' :)

As in light propagating (a 'beam'), reflected from some (BH) center and then passing a event horizon outwards to the universe?
No

As in there being principles and laws defining an balance in where black holes too should interact with the rest of the universe?
Yes

But as Pete wrote, that's a tricky one

[guest45734]

I forgot to mention yesterday that energy/mass can escape BH's as gravitational waves as was detected by LIGO. If memory serves two BH's orbiting each other emitted gravitational waves. One BH had 29 solar masses and the other 36 solar masses, spiralling into each other to create a single black hole of 62 solar masses. Three solar masses were lost as gravitational waves which rippled through space to us a few years after.

Being lazy I didn't place a link to the merger above, here is one for completeness https://en.wikipedia.org/wiki/Binary_black_hole.
Edit found this pdf from the LIGO team https://dcc.ligo.org/public/0122/P1500218/014/PhysRevLett.116.241102.pdf

The SPECULATIVE thing ref the BBH merger from a zero energy universe point of view. Is if the gravitational wave is regarded as negative energy, then could the gravitational wave have created any kind of positive energy as it travelled away from the merger to maintain a zero energy universe.

A photon of light has its own gravitational field and is affected by mass and gravity from other forms of energy. Hawking radiation escaping a BH will likewise have its own gravity field and be affected in the same way any other particle would be.

If a particle with +ve energy has a gravity field with -ve energy, does a gravity field escaping a BH merger also have energy in the form of radiation = to the strength of the gravitational energy.

[yor_on]

It's weird going, I remember that one too. It was formulated as the gravity waves contained the missing 'energy' from the black hole merger. And yes, where did it go? Into a distortion of SpaceTime?