TN: Difficulties in the Cellar (Jan. 17, 2011)

[Steven Spielmann]

originally posted by Oswaldo Costa:
When is anything off-topic?

I'm 93 points on this.

 

[MLipton]

originally posted by Ian Fitzsimmons:


I hadn't heard that. Are they thought to be old, disk-less galaxies that are slowly orbiting into the hole, and therefore concentrating in space; or are they distinguished from other galaxies somehow by their manner of birth? Or something else?

The origins of quasars is still a matter of debate AFAIK. One theory is that they arise from the density of stars at the center of galaxies, which then collapse into a black hole through gravitational attraction; another is that the black holes form from the dense center of a gas cloud that precedes galaxy formation; yet a third theory suggests that the initial supermassive black holes were artifacts of the big bang that then attracted matter around them that later coalesced into galaxies.

If the holes radiate EM across the spectrum, why are they 'black?' Or is their visible spectrum radiation just extremely low.

The black holes are black because no radiation emerges from within the event horizon (aka the Schwarzschild radius). The radiation that I'm talking about emerges from outside the event horizon, so you can imagine a large "accretion disk" of matter surrounding the black hole that is glowing white-hot as it emits all that radiation. Here's an artist's depiction of that:

Mark Lipton

 

[Ian Fitzsimmons]

originally posted by MLipton:

originally posted by Ian Fitzsimmons:

originally posted by Ian Fitzsimmons:
Yes, Mark; they emit hugely powerful x-ray beams, don't they - is that the same? A little knowledge is a dangerous thing. I guess in string theory, any unaccounted for energy can jump down the rabbit hole of one of the microscopic dimensions.

Anyway, thanks.

But, on second thought, to maintain balance, the radiated energy would have to be equivalent to all the energy and matter approaching the event horizon; so that, in effect, nothing is captured in the hole's gravitational field, it's just converted to energy (if it was initially mass) and propelled away. That doesn't sound right.

Why would it have to be equivalent? The radiated energy is equivalent to the work performed by gravitational attraction. Any mass not radiated away as electromagnetic energy is added to the mass of the black hole. I see nothing in that that mandates a strict equivalence in mass/energy.

Mark Lipton

Well then you get back to my initial question. I guess it should be rephrased as How can mass and energy be be concentrated at a dimensionless point?, rather than How are matter and energy conserved? But perhaps I'm also wrong in thinking that mass in a black hole is thought to collapse to a dimensionless point.

 

[SFJoe]

No one knows what's inside, but you can calculate the diameter for the event horizon--it's just the radius where the escape velocity is c. So light black holes are small (and much more radiant), and heavy ones are big. The radiation is mostly from things falling in, not from the holes themselves. Big ones are quite stable.

 

[Ian Fitzsimmons]

originally posted by MLipton:

originally posted by Ian Fitzsimmons:


I hadn't heard that. Are they thought to be old, disk-less galaxies that are slowly orbiting into the hole, and therefore concentrating in space; or are they distinguished from other galaxies somehow by their manner of birth? Or something else?

The origins of quasars is still a matter of debate AFAIK. One theory is that they arise from the density of stars at the center of galaxies, which then collapse into a black hole through gravitational attraction; another is that the black holes form from the dense center of a gas cloud that precedes galaxy formation; yet a third theory suggests that the initial supermassive black holes were artifacts of the big bang that then attracted matter around them that later coalesced into galaxies.

If the holes radiate EM across the spectrum, why are they 'black?' Or is their visible spectrum radiation just extremely low.

Okay; I'd only heard that black holes result from supernovas of supermassive stars, the collapsing mass of which becomes is sufficiently great to overwhelm both electron and neutron degeneracy pressure. Thank you for these new (to me) ideas.

originally posted by MLipton:
The black holes are black because no radiation emerges from within the event horizon (aka the Schwarzschild radius). The radiation that I'm talking about emerges from outside the event horizon, so you can imagine a large "accretion disk" of matter surrounding the black hole that is glowing white-hot as it emits all that radiation. Here's an artist's depiction of that:

Mark Lipton

I'm still confused: if there is EM radiation at the event horizon, it would define a visible shape, albeit at the event horizon, rather than at the hole itself. But it sounds here like you're saying that the radiation is emitted by energy-matter approaching the horizon, rather than the horizon itself, so I probably misunderstood you before. Typical.

Thanks again.

 

[Oswaldo Costa]

Mark, I am having difficulty with the artist's rendition, can you find us a different one? Those pink puff balls spinning off the event horizon like interstellar cotton candy are giving me the creeps.

 

[Ian Fitzsimmons]

originally posted by SFJoe:
No one knows what's inside, but you can calculate the diameter for the event horizon--it's just the radius where the escape velocity is c. So light black holes are small (and much more radiant), and heavy ones are big. The radiation is mostly from things falling in, not from the holes themselves. Big ones are quite stable.

Да правда, but no one's witnessed neutron degeneracy collapse either, I think; the inference is made based on what we think we do know and some mathematical calculation. Perhaps we don't understand subatomic particle dynamics well enough to form conjectures about what succeeds neutron degeneracy.