Slashdot Mirror
Why Some Supermassive Black Holes Have Big Jets
astroengine writes "Some of the supermassive black holes at the centers of galaxies have powerful jets blasting from their poles, and others have weak jets, but many don't have jets at all. Why is this the case? In new simulations carried out by astronomers at NASA and MIT, it would appear that the way in which the black hole spins relative to its accretion disk may be a contributing factor. Strangely enough, the results indicate that if the black hole rotates in the opposite direction to its accretion disk, the most powerful jets form. The region between the black hole event horizon and the accretion disk still baffles scientists, so these simulations are very speculative, but the results seem to match what radio astronomers are seeing in the cores of active galaxies. Perhaps it's time to fire up that event horizon telescope!"
They also decrease in mass by emitting hawking radiation.
http://en.wikipedia.org/wiki/Hawking_radiation
MACHO: Massive compact halo object
An alternate theory is WIMP. You can imagine which ones the nerds prefer.
the growth in cynicism and rebellion has not been without cause
You never see the singularity supposed at the middle of a black hole. A black hole, is normally defined by its event horizon a spherical (spheroidal for a spinning) hole, region light can't escape from. A black hole can have spin and charge, because these are both universally conversed quantities.
Black holes are regions of spacetime from which light cannot escape (nor can any other known form of matter or energy). The boundary of that region is called an event horizon. In classical General Relativity, there is a singularity inside the black hole. For a spinning black hole (described by the Kerr spacetime), this singularity is a ring around the axis of rotation, if that makes you feel any better. But in the end, talking about the motion of the singularity is meaningless - space and time do not exist in any normal sense at the singularity - it is called a singularity because the definitions of space and time break down there (the curvature of spacetime becomes infinite). If there is no space and no time, what does it mean to "rotate"? In fact, it is the spacetime at and outside the horizon that carry angular momentum (as compared to an observer at infinity). What that means is that objects near a rotating black hole which feel that they are locally "at rest" will still be rotating around the black hole from the perspective of an observer very far away from the black hole because the spacetime itself is being dragged around the black hole. Finally, for the record, singularities in spacetime are widely believed by physicists to indicate a failure of the General Theory of Relativity to describe extremely high curvature regions and not actual physical objects in our universe. We hope that if we can ever reconcile General Relativity and Quantum Mechanics that the resulting theory will be singularity free. Does that clarify things?
Since it now appears that many galaxies, and possibly every single spiral galaxy, is the result of galactic "collisions", I imagine that although in any undisturbed galaxy the central black hole will rotate precisely the way the rest of the galaxy does, following galactic mergers, things can end up a little topsy-turvy. The naturally tendency would be for these collisions and mergers of the central cores of galaxies to bias towards the existing spin (since it will influence the merger itself), so the majority of resulting mergers will maintain a spin in the same direction as the larger galaxy prior to the merger, in some cases, it's going to be a bit out of whack. Particularly after many repeated mergers (and there's evidence that many if not most larger galaxies end up gobbling up a number of smaller galaxies during their lifetimes), some are going to end up with core configurations completely opposite of their original state.
"Convictions are more dangerous enemies of truth than lies."
You may be thinking of the 'White Hole' theory.
http://curious.astro.cornell.edu/question.php?number=108
http://en.wikipedia.org/wiki/White_hole
I have only a most basic grasp of cosmology but it's an interest of mine and I recall watching something on documentary heaven to the effect that black holes may well be a universe of their own
One of my most favorite books on the subject is called The Five Ages of the Universe by Adams and Laughlin. If you like reading books about the subject but don't care about or can't comprehend the math, I seriously recommend it. That said (and I think it's in the book I linked), there's an evolutionary theory about universes that contends each time a black hole is created, it splits off a unique instance of spacetime creating a "new" universe with its own laws of physics. Universes created in this manner that contain laws of physics favorable to the creation of black holes will go on to evolve new "child universes" of their own; a sort of cosmic equivalent of Darwin's natural selection.
;)
One more thing, should you find yourself occasionally staring at the TV and wanting to feel educated and entertained, then you should, uh, "acquire" a copy of Into the Universe with Stephen Hawking. It's a very well written and well narrated version of how Hawking explains the workings of the universe, but unfortunately isn't available on DVD yet. However, the trusty folks on the web that don't make any money from TV and movie distribution should have a copy you can pick up today
The extremely fun thing about physics from a layman's point of view is that there are so many theories about how the same things work, and getting them presented to you in a manner you can understand without knowing the math behind it is a wonderful thing. From there, you can theorize and come to your own conclusions about which you like best, because if Planck has anything to say about it, we'll never truly know which of them is right.
It's kind of like going to a trade show, only instead of the place being full of vendors, it's full of missionaries from every major religion on the planet, and you get to objectively pick the one you like the best. I'm sure most Slashdotters would be drinking the free coffee at the Atheists' booth or ignoring everyone and speculating what the giant bundle of Cat5 on the wall goes to, but regardless of whether your God is supernatural or nonexistant, to glimpse into the very fabric and inner workings of the cosmos is the only true way to see into that mind.
Still, even if that's not the way you see it, I do feel that it's also the only way to even begin to fathom what we all really are.
Boot Windows, Linux, and ESX over the network for free.
Yes, there is a direct relationship between the radius of the event horizon and the mass-energy within the event horizon. More massive or more energetic black holes have broader event horizons. This is observer dependent and subject to a Lorentz contraction, so if you are accelerating directly towards a black hole it will appear more massive (and thus have a larger radius) than if you are accelerating directly away from the same black hole; this effect increases exponentially as (absolute) relative velocity increases towards c.
When any observer sees mass-energy crossing into the event horizon, the event horizon's radius increases proportionately. Again an observer's measurement of that mass-energy is subject to a Lorentz contraction.
There is also an inverse relationship between the surface area of the black hole and its temperature; both are subject to the same Lorentz contraction, but more massive black holes emit photons similarly to colder blackbody radiators than less massive black holes.
We have no useful theory about what's going on the inside of an event horizon.
There are several ways to consider the microscopic states inside a black hole from a thermodynamics-meets-General-Relativity perspective. Here's one. In GR (and we have tested this), the lower the gravitational potential in which a clock is, the slower it ticks, for any form of clock (including naturally oscillating processes). Ignoring observers experiencing acceleration other than via gravitation, the gravitational potential is very high in inter-galactic-cluster space (i.e., farrrr away from dense mass-energy), lower inside solar systems, lower still on planetary surfaces, very low inside stars, and extremely low inside black holes. Consequently, a "clock" ticking inside a black hole will, from the perspective of someone with a high gravitational potential, tick very slowly. The "clock" itself, however, will always tick at its natural rate, from its perspective and the perspective of anything immediately near by it, unmoving, and at the same gravitational potential.
So from our perspective on Earth, a natural oscillator inside an event horizon will go from oscillating at, say, several GHz, to oscillating less than once every several billion years of our time.
From its perspective our clocks on Earth will speed up by the same factor.
However, where things get strange is where the gravitational potential changes in distances shorter than the wavelengths of protons, neutrons, electrons, photons, and so forth, since they are ultimately oscillating "clocks". If "part" of a proton is in a higher gravitational potential than the rest of it, how do the quarks and gluons within it behave? What happens to the proton? And so forth.
That requires a consistent unified theory of gravitation and quantum mechanics, which nobody has been able to demonstrate yet.
Electrons, Protons, and Neutrons obey Fermi-Dirac statistics for fermions. Spatially, this means that you can't stack them all in one place - there is a pressure separating fermions from one another. When you introduce pressure from, for example, gravitation in a heavy star, it overwhelms the fermionic pressure and creates "degenerate matter". Neutron stars have degenerate phases including neutrons formed by squashing together electrons and protons. Quark stars may exist, and would have degenerate phases formed by squashing together heavy (i.e., full of neutrons) atomic nuclei. Pressures at and inside an event horizon would almost certainly lead to some further degenerate phase, and we have no idea what happens then.
(We can somewhat reproduce some
For pity sake
1) The matter in a black hole isn't missing. It's accounted for. We can't know what kind of matter is in there because we can't know anything about stuff beyond the event horizon
2) We still don't know what Dark matter is, but we know that the so called WIMP model is most likely to account for most of it. We know this due to studies of objects like the bullet cluster of galaxies which can't be explained by MACHOs. In the bullet cluster, you see 2 galaxies that have collided - the normal matter in the form of gas and dust in each galaxy got slowed down, but the dark matter passed through each other. That wouldn't happen with MACHOs, and we would expect to be able to detect MACHOs in such a matter rich area by their microlensing events.
http://www.universetoday.com/2010/03/01/what-can-the-dark-matter-be/
http://www.daviddarling.info/encyclopedia/D/darkmat.html
3) What's even more interesting is that recent work suggests black holes do not absorb dark matter
http://www.universetoday.com/2010/03/22/astronomers-find-black-holes-do-not-absorb-dark-matter/#more-60422
These posts express my own personal views, not those of my employer
No black hole we can indirectly observe actually loses mass, though: it would have to be of less mass than the moon to overcome even the background cosmic radiation, let alone the radiation in the environments we're observing. The black holes at the center of galaxies, well, they won't even be evaporating when the universe is twice as old as it is now.
I guess I shouldn't be surprised that we'd cite wikipedia without reading or understanding it.
The math breaks down at the Event Horizon because of the expression
Delta Tau^2 = (1-2M/r)dt^2 - dr^2/(1-2M/r)
Where Delta Tau is the invariant interval, 2M is the Distance from the singularity to the event horizon and r is the reduced circumference.
At the event horizon, where r = 2M, the equation breaks down.
The math breaks down at the Event Horizon because of the expression
Delta Tau^2 = (1-2M/r)dt^2 - dr^2/(1-2M/r)
Where Delta Tau is the invariant interval, 2M is the Distance from the singularity to the event horizon and r is the reduced circumference.
At the event horizon, where r = 2M, the equation breaks down.
Neither the math nor the physics break down at the event horizon, the Schwarzschild coordinates does for that particular spacetime, but that's just a problem with Schwarzschild coordinates. Much in the same way polar coordinates are not well behaved at 0, but the space R^2 is. There are several ways to check this, you could calculate curvature invariantes like the Kretschmann invariant and check that it doesn't blow up there, or you could use another chart (Kruskal-Szekeres for example) which are perfectly well behaved at the event horizon. The only true singularity for that spacetime is at r=0, the curvature actually becomes infinite at that point.
Unfortunately misleading messages like parent plague slashdot science oriented articles and get modded as informative.