Slashdot Mirror
Hundreds of Black Holes Found
eldavojohn writes "Hundreds of black holes that were thought to exist at the beginning of the universe have been found by NASA's Spitzer and Chandra space telescopes. From the article, 'The findings are also the first direct evidence that most, if not all, massive galaxies in the distant universe spent their youths building monstrous black holes at their cores. For decades, a large population of active black holes has been considered missing. These highly energetic structures belong to a class of black holes called quasars. A quasar consists of a doughnut-shaped cloud of gas and dust that surrounds and feeds a budding supermassive black hole. As the gas and dust are devoured by the black hole, they heat up and shoot out X-rays. Those X-rays can be detected as a general glow in space, but often the quasars themselves can't be seen directly because dust and gas blocks them from our view.' This is pretty big, as it's empirical evidence proving the existence of objects that theoretically had to exist but could not be detected previously."
but where does that stuff come from? And how did it get there?
IANAA (I am not an astrophysicist) but I seem to remember, from the astronomy course which I took for fun in college, that stars formed out of hydrogen present after the big bang (the hydrogen formed soon after everything cooled down enough to allow protons and electrons to bind together again) which formed stars due to minute temperature variations throughout the universe (apparently if the temperature were entirely uniform then nothing interesting, including ultimately Humans, would ever have formed out of the large soup of hydrogen that was left over).
Now, depending upon the initial mass of a star and its final disposition (white dwarf, brown dwarf, neutron star, supernova, black hole) which depends upon that mass, the star creates ever heavier elements as the fusion of hydrogen into helium progresses into the fusion of Helium into Lithium and Lithium into Boron and so on all the way up to Iron (which is the heaviest element that can be produced by fusion). The elements that are heavier than Iron are produced in the massive pressure and forces generated by novas and super novas. Obviously this process has happened over and over again as matter and stars coalesced by gravitational attraction into the galaxies that we see today (lots of handwaving here, again IANAA).
Now, to answer your question, since dust is probably mostly carbon type stuff and compounds (which form pretty often in giant red stars) then over time as stars form and explode and form and explode and form and turn into black holes there will ultimately be some black holes surrounded by stray gases and dust from its own nova or surrounding novas or nearby stars over large periods of time. Lots of handwaving here, but does this answer your question?
"This is pretty big, as it's empirical evidence proving the existence of objects that theoretically had to exist but could not be detected previously."
look closely
"empirical evidence proving"
should never occur in any sentence ever. By definition empirical evidence cannot prove anything. Empirical evidence lends support to inductive arguments, which don't concern themselves with proof. Only analytic statements may be proven.
Please, for the love of god remember, there are two forms of logic, inductive which has arguments from experience (physics), and deductive which has arguments from pure reason (mathematics). Only deductive arguments can be proven because you can always argue with the strength of the evidence in inductive claims. It is a fact (supported by inductive evidence and deductive proofs) that inductive claims may be false no matter how strong the evidence for them is. Thus they can never be proven, but you can say "there are strong practical reasons to believe."
People getting basic logic wrong has led to a lot of poor decisions in our society lately, so please do not contribute to the problem by adding to confusion over terms.
google example Replace the mass with any interesting value.
Fnord.
The black holes seen by Spitzer are supermassive black holes (i.e., black holes with a few million solar masses). These black holes will not evaporate for a long time.
What is generally taken to be the reason that the density of Active Galaxies is less high currently than at higher redshifts in the earlier universe is that the matter required to fuel the Active Galaxies is exhausted. This does not mean that these black holes do not exist anymore, just that it is virtually impossible to detect them. But the general assumption of most astrophysicists is that they are still around and in the centers of most, if not all, galaxies. For example, our own Milky Way has a supermassive black hole at its center. Its brightness is very low, so were this black hole not so close, relatively speaking, we would not be able to detect it at all.
Except, of course those micro-black holes couldn't exist, at least given our current understanding of stellar evolution. Post-supernova, without enough mass, neutron degeneracy will prevent the remains of our dead star from falling below the Schwartzchild radius. It's theorized that the minimum mass to form a black hole is about 2-3 times that of the sun, so the smallest black holes would probably have a 6km event horizon.
Well, the Earth is pulling the moon towards it too, and yet we still have a moon after all these billions of years. The Sun is pulling the Earth towards it, but, funnily enough, after all these billions of years we're not quite there yet.
In a sense, the Hitchhiker's guide got that right: ""There is an art to flying, or rather a knack. It knack lies in learning to throw yourself at the ground and miss. Clearly, it is this second part, the missing, that provides the difficulties."" We keep falling in an almost circular orbit around the Sun and ending up (almost) where we started.
What I'm trying to say is that those super-massive black holes obviously do suck everything towards them. But the rest of the galaxy sees it as centripetal force and rotates around them.
The problems with a black holes are at closer ranges.
For a start, if you do get closer to it than its event horizon, then you're properly fucked. There is no way to get out of there, not even theoretically. Not even light can get out of there. Hence, the name black hole.
However, I'll return to the analogy with the solar system. With the Sun's massive gravity well, it's damn near impossible to hit it, even if you wanted to. If you dropped a big rock right at it, even the slighest deviation or initial speed sideways (like would happen if you dropped it from Earth), would cause a clean miss and you'd just get that rock in some kind of orbit around it. The only way to actually hit the sun would be if that orbit was flattened enough that it passes through the sun.
And the same problem applies to black holes too. Remember that it's a more massive gravity well _and_ the "bullseye" is much smaller, at least in relation to the gravity well. As you fall even a little off the centre, your speed would increase enough so at one point the centrifugal force (yes, I know it doesn't even exist, but it makes the explanation easier) just flings you clean around it.
There's even at least one theory that nothing ever finishes falling into a black star. Although there is energy loss due to that X-ray emission and all, basically matter just spirals closer and closer to the event horizon without ever reaching it. Think an asymptotic decay. It gets closer and closer and closer over time, but never quite reaches it.
The second problem is, well, tides. If you get close enough to the centre of a gravity well, say, looking at the centre, then your front is pulled towards it much stronger than your back is.
This is actually true for any gravity well, and, again, you can see it in action in the solar system too. That's why the moon is tidal-locked with the Earth and you always see the same face of it.
But for a massive enough gravity well, the force difference gets larger and can rip a star or a planet apart. That's how stars and black holes end up occasionally peeling another star apart, pretty much syphoning its outer layers.
So basically you could be past the event horizon and still be properly fucked, in slightly different way.
But even that only extends so far. IIRC there are stars orbitting the centre of a galaxy with a period measured in hours. Admittedly, that's not as close as it might suggest, again because of the massive gravity. Even with that angular speed, you still need a heck of a radius to stay in orbit there. But, still, if those survive just fine, then you can probably see how the rest of the galaxy is safe.
A polar bear is a cartesian bear after a coordinate transform.
I am an astrophysicist, so let me try and explain in a little bit more detail why this result is so interesting.
First of all: No, the discovery of these black holes has nothing to do with questions concerning the dark energy or missing mass. Note that one has to distinguish between dark energy or missing mass. What is meant by missing mass is the fact that in order to explain the rotation of many galaxies we need to invoke about 10 times more mass than what is found from observing the galaxies. What we do here is that we look at the rotation of the galaxies from which it is possible to infer their mass using simple dynamics arguments. In order to infer the mass present in a galaxy independently of the dynamics, you can simply make a picture of it. Since we know that typical stars have about the luminosity of the Sun it is then possible to calculate from the observed light how much radiating matter is present in the galaxy. It turns out that to explain the observed motions, about ten times more mass is required. Similar arguments also apply to galaxy clusters. This is what's called the missing mass.
Dark energy, on the other hand, is a term proposed in the Einstein field equations, and therefore also in the Friedmann-Equations, which describe the expansion of the universe. With a so-called cosmological constant, these equations predict an accelerated expansion of the universe. It turns out that this is what's observed. About 85 percent of what is causing the curvature of the universe (the so-called Omega-parameter) is due to this cosmological constant, and many astronomers call the cosmological constant "dark energy". There is a nice plot by Mike Turner summarizing the different terms that need to be added to explain by the observed matter density of the universe.
To turn to the question as to why we astronomers were looking for black holes enshrouded in gas: there is a long standing question about the number density of black holes in the universe. We know that in the local universe most galaxies, including our milky way, harbor a supermassive black hole in their center. These black holes are difficult to find since most are just sitting there, doing nothing. The mass of such a black hole is on the order of one million to one billion solar masses. This sounds a lot, but is really not very much: the typical radiating mass of a galaxy is 100 times more, and if you add the missing mass, then the supermassive black hole only contributes less than 0.1 per cent to the mass of the galaxy. So, on cosmological terms, the mass contained in these black holes is really negligable.
What matters, however, is that models for the evolution of black holes predict that there should be a large number of black holes that are enshrouded in rather dense material in many galaxies. It has been difficult to detect these objects so far, since the dense material absorbs most radiation from the accreting black hole. With infrared observations with Spitzer that are summarized in the press release the Slashdot posting points to it has finally been possible to confirm the long-standing assumption that these black holes exist. What is the nice thing in all of this is that these observations confirm the predicted space density of black holes inferred from previous observations, which is a very nice and important result.
Glancing through the article some more, I grant that I am somewhat incorrect. The key difference is that an ECO will decay much faster than a pure black hole with no photon radiation pressure would. Recall that we still have Hawkings radiation to eventually eliminate the massive object. Also recall that a considerable portion of the mass of some massive objects (particular those in the center of galaxies) might have a large "dark matter" component which in turn might be matter that won't convert into photons or other massless particles.