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Possible Hole in Black Holes
jd writes "Researchers have found what they believe may be a MECO (Magnetic, Eternally Collapsing Object) inside of a quasar. MECOs are rivals to black hole theory and involve plasmas that never reach the state of being a singularity. The most obvious differences between them are that MECOs have a magnetic field and do not have an event horizon. The problem lies in that the Universe cannot have both MECOs and black holes — it can only have one or the other. If this object truly is a MECO, then black holes do not exist. Anywhere. (Furthermore, this would require Professor Hawking to return a year's subscription to Private Eye and give Professor Thorne a year's subscription to Penthouse.) On the other hand, if this thing isn't a MECO, it's behaving very very oddly for a black hole."
I was reading it fine until I hit the word "Penthouse", then I forgot everything else and had to look it up:
1 4/2330221
n g_an_old_bet
http://science.slashdot.org/article.pl?sid=04/07/
http://en.wikipedia.org/wiki/Stephen_Hawking#Losi
Seriously, if this thing really is an MECO then what are all of the things that we've thought were black holes?
Probably MECOs.
Because it's 3 AM, and I don't have the energy to reproduce all the math, there's two main theories about super-massive objects (simplifying a lot).
One: Black holes. You've got an event horizon. Anything passes that point is gone forever. And they don't have magnetic fields. (remember, simplified massively)
Two: MECOs. No event horizon, instead the matter pulled in is spun for a while then ejected at near lightspeed. They do have magnetic fields.
Everything we know about black hole candidates falls into one of two sets of mutally exclusive equations (in large part to the magnetic field thing).
That this object appears to have a magnetic field supports one set of Einsteinian equations; the one that supports MECOs.
I like you, Stuart. You're not like everyone else, here, at Slashdot.
Preface: I have a Ph.D. in Astrophysics and my ressearch has to do with computer models of black holes.
This is yet another one of these things where an observational astronomer who just doesn't like black holes comes up with some incredibly complex theory to explain their oberservations so they don't need a black hole to explain them. There is an incredible resistance towards black holes in some parts of the astronomical community. Saying that "A black hole can't do this" when our models of accretion discs arount black holes are still at the state they are in i.e. fixed background metric, many models are only HD not MHD (no magnetic fields in the disc) is just not backed up by the facts.
This reminds me of the whole "we don't need black holes to explain jets" discussion a couple of years back.
Besides I do not se how the existence of Mecos would prevent the existence of black holes in general. We are still using the same Einstein Equations, right?
I think the operand word in the article is "controversial". Occam's Razor is a good rule of thumb.
Is it possible that, as I think I once read here on Slashdot, some cosmological constants may really be variables that shift very slowly as the universe ages, and that MECOs were thus possible then, but no longer are
I am an astrophysicist but not a general relativity (GR) or cosmology person; take the following with a grain of salt. As far as I understand all solutions of GR equations involving singularities require some assumptions, since they need to take quantum effects into account and we do not have a theory of quantum gravity. So, we should be living in a very interesting universe if a few parameters about quantum gravity had such values and changed in such a way that MECOs were possible in the past and black holes are possible now. It is certainly possible, but if this happened I would suspect that there is a deeper reason for this.
ato
Just skimmed it. This theory definitely does not exclude the existence of black holes. This is just another solution to the Einstein equations, involving matter.
If the contraints they impose on the stress-energy tensor (i.e. the the assumptions they make about the behavior of matter) are always enforced in the universe, I think they'd have a problem with creating neutron stars.
"consensus" is a fourth declension noun (in Latin) so it's plural, properly, is "consensus." No change. Who knows what it is in English though.
The definition of a black hole does NOT require a singularity. What the strict defintion requires (as in Hawking and Ellis, or Wald's "General relativity) is that the black hole region in an asymptotically simple spacetime is the region that is causally disconnected from future null infinity.
In English: once you go into one, you can never get back out if you believe that nothing can travel faster than light. If you CAN get out, the thing you started with was not a black hole!
Notice that for the concept of black hole to make sense, you do not need general relativity. You do need to believe that there is an ultimate speed limit, and then the black hole of any theory is the region you cannot escape from.
It is then a THEOREM of (classical) general relativity that such a region contains a singularity. If GR is corrected by some version of quantum gravity where there are no singularities, then this theory can still have black holes (regions of no escape).
Now this is a stricter sense in which black holes are talked about currently. The article mentions Hawking and Thorne's disagreement: is information carried off by Hawking radiaiton? The answer is no: if the information goes in then it cannot come out by (the strict) definition of what a black hole is. Technically, the argument about the information loss problem is whether or not black holes (as originally defined) exist at all!
However, this is an arguement purely at the level of sematics. There is very little observational difference between a real black hole [one that locks information up forever] and an information returning black hole [one that locks up and processes particles for a long period of time, but the end result of this process is re-emission as Hawking radiaiton]. Because the definition given above is one made for convience, most researchers in the field take a somewhat more pragmatic definition of a black hole.
The theory of MECOs seems to still be built on General Relativity. It claims that radiation increases to stop complete collapse. This does not preclude the existence of black holes! It just means that they are unlikely to form as the end result of astrophysical processes. However, there are situations where you can make black holes at very low temperatures, or ones that you can do in flat space (although these tend to be somewhat artificial).
The moral is
* MECOs are built on GR. If MECOs exist, then black holes are still solutions to GR
* The MECO advocates claim that this is a universal process for very hot and dense gas. We should not expect that black holes are a typical end of stellar product.
* MECOs may exist, but the process may not be universal (i.e. it may require particular thresholds of energy/pressure). This would allow a mix of black holes and MECOs.
* There may be no MECOs at all.
Personally I am dubious that MECOs exist at all. Pressure *can* support a star against collapse, but only to a certain extent in GR. After a while, the pressure required also acts as a stronger source of gravity and ends in a runaway reaction causing collapse. See this paper of mine for more details: http://arxiv.org/abs/gr-qc/0306038