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Hidden Black Holes Discovered
mknewman wrote to mention a Space.com article discussing the discovery of a large group of hidden black holes. From the article:"Black holes cannot be seen directly, because they trap light and anything else that gets too close. But astronomers infer their presence by noting the behavior of material nearby: gas is superheated and accelerated to a significant fraction of light-speed just before it is consumed. The activity releases X-rays that escape the black hole's clutches and reveal its presence. "
what was there when it all started: galaxy or a black hole?
Gee, doesn't that make you feel oh-so-safe for our upcoming space travel (many lifetimes ahead of us)... "a large group of hidden black holes." pot holes of the universe? You think driving is bad *now*...
Light and x-rays are the same things (as you imply), just at differing frequencies. Visible light can escape from outside black holes' event horizons, just as easily as x-rays.
Any electrical charge undergoing an acceleration emits radiation, if it can couple to its environment. Charges which are accelerated more emit radiation at higher frequencies, and accelerations near a black hole's event horizon are very large, so x-rays are emitted preferentially over visible light. There is also an effect of higher frequency emissions from any finitely-sized source being more "focused" than lower frequencies. This leads to more concentrated "beams" of emission from finite sources.
Finally, one of the methods of radiation from black holes is that of spontaneous particle-antiparticle production in the tremendous gravitational gradient outside a black hole. Normally, these particle-antiparticle pairs recombine quickly. However, if one travels nearer a black hole than the other (they're emitted going in opposite directions relative to their center of mass, to combine linear momentum), it can get sucked down the gravity well, and the other escapes.
I forgot to mention one of the most imporant effects: matter which is around a black hole tends to form accretion disks. It forms disks because it tends to have a net angular momentum about the black hole's center, and so spins. The fact that differing parts of the accretion disk move at different speeds means that there is a lot of rubbing going on -- not unlike with slashdot readers. This leads to heating of the accretion disk, often up to a very high temperature; the accretion disk is just like a very hot oven, which doesn't emit (much) in the visible region, but a lot in the x-ray region of the spectrum. There are also tremendous focusing effects of magnetic field lines (accelerating charges again), and so the emitted radiation tends to get focused along opposing "jets".
Beware, the article is quite technical:
If you extrapolate our 21 quasars out to the rest of the sky, you get a whole lot of quasars.
Better yet, how about its mass compared to the Moon, and how many AU is the Moon from the Earth?
Think of it this way:
Most black holes are for obvious reasons of stellar mass, i.e, less than 20 times the mass of our sun. 20 AU doesn't even get you out of this star system--Pluto is 30 AU or so out. So the contribution of those black holes is going to be completely swamped by the sun.
The supermassive black hole at the center of the Milky Way is thought to be in the neighborhood of a 10^6 solar masses; the galactic center lies about 2x10^9 AU in the general direction of Sagittarius, so any contribution from it will also be swamped by the sun.
Nothing outside our solar system is likely to have any measureable gravitational effect on anything inside it other than the entire system orbiting the galactic center.
Example: It is possible, at room temperature and pressure, to have pure water at 105 degrees celcius and NOT have it boil. It is very unstable and will generally boil vigorously the moment you get any kind of circulation within the water.
Second, Quasars (Quasi-Stellar Objects) are, as yet, undefined. Nobody knows what drives them, so to call them super-active Black Holes is blatantly absurd. They are also frequently at the very edge of the visible Universe, making it very unlikely anything large enough to collapse into a super-massive Black Hole could have existed - let alone existed long enough to actually undergo gravitational collapse.
Besides which, such objects are not near. This is important. Black Holes evaporate, but they don't evaporate THAT quickly. A Black Hole the size of a typical Quasar would need to be absolutely gigantic and would not have evaporated in this time even if no other matter had fallen in.
Indeed, there are NO quasars closer than 5 billion light-years away - a distance referred to as the "red-shift cutoff". If Quasars were galaxy seeds, you would expect them to fade into the age of galaxies, not dramatically and suddenly cut off entirely.
The idea that Quasars then formed into galaxies is improbable - the diameter of a Black Hole is a direct function of the mass of the Black Hole (which includes the mass and effective mass of everything it consumes). It is unlikely that there are any galaxies large enough to have a Black Hole of the kind of mass implied by the output of a typical Quasar.
If a Quasar were powered by a Black Hole, it would be typically 100,000 times more massive than the Black Hole at the Black Hole at the center of our own galaxy. Given that the presence of a galaxy implies that the Black Hole is still being fed matter and energy, it would be quite impossible for a Black Hole to evaporate to 0.00001% of its original size in the time available.
Remember, Earth is 4 billion years old, the Universe is only 15 billion years old. And of those 15 billion years, the Black Holes would only start to really evaporate relatively late on as the density of matter and energy declined. Actually, you don't even get all 15 billion years of that. Quasars peaked at about 12 billion years ago and as already noted, vanished entirely at 5 billion years ago. This gives you a paltry 7 billion years to shrink to the required size.
Now we get into a real mess. The Milky Way galaxy is ALSO estimated at 12 billion years old, based on the ages of known structures. There are no structures around Quasars. They'd be blown to bits. For the Milky Way to have formed around a "dead" Quasar, the Quasar must have formed considerably earlier. There are a LOT of galaxies out there as old as, or older than, the Milky Way. If all of them formed around Quasars, there would have needed to have been more of these really early starters than existed at the height of the reign of Quasars.
There is another problem. The Milky Way belongs to a local cluster of galaxies. If they ALL had formed around dead Quasars, the Quasars would have fallen into each other from their gravitational pull LONG before there was any possibility of a galaxy forming.
Nor are Black Holes strictly "hidden". They always emit Hawking Radiation, although there are no good detectors for this at present. That is hardly the fault of the Black Holes, though - if they're not seen, it's because the observers aren't looking.
As for the number of Quasars - there are only 39 known Type II Quasars
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
When asked why it took this long to discover the nature of the strange space phenomenon, Mark Lacy of the Spitzer Science Center at the California Institute of Technology replied:
"Well, the thing about a Black Hole, its main distinguishing feature, is it's black. And the thing about space, your basic space color, is black. So how are you supposed to see them?"
"Derp de derp."