Cygnus X-1

[Ian]

If Cygnus X-1 is a black hole, then there could be particles coming out of it. Stephen Hawking and Kip Throne had a bet about whether or not Cygus X-1 was a black hole. I hope that it is eventually settled.

[bPer]

Originally posted by Ian
If Cygnus X-1 is a black hole, then there could be particles coming out of it.
Care to explain that statement?

βPer

[Ian]

I meant that there should be particles coming out of it like in other black holes like the one that is believed to be at the center of our galaxy.

[bPer]

Originally posted by Ian
I meant that there should be particles coming out of it like in other black holes like the one that is believed to be at the center of our galaxy.
Ok, first off, the particles aren't coming out of the black hole; they're coming out of a disk of material that orbits the black hole, called an accretion disk. You do realize that a black hole is called that because nothing (matter or energy) escapes it, right? If you don't, time to head off and do some research.

Beyond that, you're getting into parts of astronomy that I only have a passing knowledge of, being basically an observing amateur. However, my understanding is that Cygnus X-1 is thought to be a binary system (if you don't know what a binary is, go look it up) where one star is a relatively-small black hole. That's where the x-rays (not particles) come from - from its accretion disk. When this phenomenon occurs, I believe astronomers call it a 'micro-quasar'. Note that, AFAIK, a quasar is quite different in structure to this.

Also (and this gets to my first question), it is not necessarily the case that a black hole produces a micro-quasar or a jet of particles. AFAIK, that is only the case in certain circumstances, like a black hole that is spinning very rapidly. I don't think you can assume "black hole = jet".

Also, I'd be careful about comparing this purported black hole to the one at the centre of our galaxy. This one is small (in the same order of magnitude in mass as our sun, if I recall correctly) whereas the one at the centre of the galaxy is thought to be millions of times more massive.

βPer

[Ian]

So the Star's matter gets attracted by the gravitational well of the black hole and it goes around it and then x-rays are produced. It doesn't actually come out of the black hole. Right?

[bPer]

Originally posted by Ian
So the Star's matter gets attracted by the gravitational well of the black hole and it goes around it and then x-rays are produced. It doesn't actually come out of the black hole. Right?
Yes, that is more or less my inexpert understanding of the current thinking. The matter drawn off from the 'normal' star is heated to very high temperatures in the immense gravitational field close to the event horizon of the black hole, and this hot matter emits x-rays. IIRC, the gravitational field is so immense that it can even tear apart individual atoms.

βPer

[jj]

Originally posted by bPer
Yes, that is more or less my inexpert understanding of the current thinking. The matter drawn off from the 'normal' star is heated to very high temperatures in the immense gravitational field close to the event horizon of the black hole, and this hot matter emits x-rays. IIRC, the gravitational field is so immense that it can even tear apart individual atoms.

βPer

What about quantum evaporation of a black hole?

While I don't mind most of what you've said, you seem to be dismissing quantum evaporation, something that I believe Hawking proposed.

[bPer]

Originally posted by jj
What about quantum evaporation of a black hole?

While I don't mind most of what you've said, you seem to be dismissing quantum evaporation, something that I believe Hawking proposed.
Can't dismiss something you've never heard of! As I have mentioned several times, I'm no expert in these matters. My interests lie mainly in the realm of what an amateur can observe. I went beyond that to engage Ian in his questions, with what little I have gathered about the subject of black holes. I am not at all surprised to find that my knowledge in this area is lacking.

So, please, fill us in. What's quantum evaporation?

βPer

[Donks]

Originally posted by bPer
Can't dismiss something you've never heard of! As I have mentioned several times, I'm no expert in these matters. My interests lie mainly in the realm of what an amateur can observe. I went beyond that to engage Ian in his questions, with what little I have gathered about the subject of black holes. I am not at all surprised to find that my knowledge in this area is lacking.

So, please, fill us in. What's quantum evaporation?

βPer

Try googling "Hawking Radiation." My knowledge in astronomy and Quantum Mechanics is basic at best, so I won't pressume to be able to explain it any better than a google search can.

[bPer]

Originally posted by Donks
Try googling "Hawking Radiation." My knowledge in astronomy and Quantum Mechanics is basic at best, so I won't pressume to be able to explain it any better than a google search can.
Thanks for the tip! Interesting stuff. I just finished an initial browse of the top few hits. One thing stood out, regarding this discussion:

Source (http://casa.colorado.edu/~ajsh/hawk.html) Black holes for which astronomical evidence exists have masses ranging from stellar-sized black holes of a few solar masses, up to supermassive black holes in the nuclei of galaxies, such as the 3×109 solar mass black hole at the centre of the galaxy Messier 87. The Hawking radiation from such black holes is minuscule. The Hawking temperature of a 30 solar mass black hole is a tiny 2×10-9 Kelvin, and its Hawking luminosity a miserable 10-31 Watts.
So, jj, in response to your comment, it sounds to me like the Hawking radiation from the Cygnus X-1 black hole would be swamped by the x-rays emitted from the accretion disk. Doesn't mean it isn't there, but probably isn't observable or relevent.

Neat stuff!

βPer

[jmercer]

Not that I'm an expert on quantum anything, but I've read up on this particular issue since following this kind of thing (and astronomy) are hobbies of mine.

First off, I believe that Kip Thornton conceded the bet about Cygnus X-1 to Stephen Hawkings a few years ago. I don't recall why, but I think it had to do with some new observation equipment put into orbit that provided evidence about it.

Regarding "evaporation" - the theory goes thus:

There is a sort of quantum "foam" (generated by the randomness at the quantum level) that permeates the universe. It's constantly "bubbling", and emits something called "imaginary particles" which are always paired in two forms - quarks and anti-quarks. Normally, the pair subside back into the "foam" and never manifest themselves as physical particles - hence the designation "imaginary".

At the event horizon of a black hole, as the foam bubbles, the pairs occasionally split because one appears inside the horizon, and one outside. I don't remember the details of why, but apparently the theory indicates that more anti-quarks will fall into the event horizon than quarks over a period of time.

The quarks that escape the pairing and the event horizon are "emitted" matter, and move away from the singularity - it appears as if matter is generated out of nowhere. As the anti-quarks fall into the singularity, they reduce the mass of the black hole since it's composed of highly degenerate - but "normal"- matter. So it appears that the black hole is evaporating - particals of mass suddenly "appear" at the event horizon and "radiate" away, while the mass of the singularity slowly decreases with each particle it "loses". (That's the appearance, but as you can see, it's not really evaporation in the classic sense of the word.)

Over an enormous amount of time, the singularities mass will eventually drop to the point where light can escape it again. I don't believe that anyone's quite worked out what will happen at that point, although there's speculation that a massive explosion could be the result.

That pretty much sums up what I recall of the evaporation process.