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TravisM
2005-Feb-06, 12:00 PM
It was mentioned at the tail end of another thread about chandra, but, I think it deserves its own little space here:

http://www.nasa.gov/missions/deepspace/chandra_chandrasweb.html

However, I'm always worried about being ToSeeked...
:-?

John Kierein
2005-Feb-06, 02:39 PM
There's more here:
http://www.spacedaily.com/news/darkmatter-05d.html

It's my view that light's interaction with this intergalactic plasma causes the red shift.

George
2005-Feb-06, 10:34 PM
Nice, a WHIM explains the missing baryonic universe. :)

Am I reading it right? These WHIMs are equal in baryonic mass to the known baryonic matter? #-o

(What are the popsicle-shaped WHIM's called? :wink: )

John Kierein
2005-Feb-07, 01:51 PM
How this is interpeted is highly dependent on whether the quasar is as distant as its red shift indicates. If the quasar has an intrinsic red shift and is much nearer, then the gas may be is more dense than the standard interpretation would say. Quasar distance is somewhat controversial, but is generally believed to follow Hubble's law in the mainstream interpretation which would lead to the extremely huge distances and huge intrinsic brightness. If the WHIM gas is spread out over this longer distance, it's density may not be great.

George
2005-Feb-07, 03:01 PM
Is the "warm-hot" energy level due to quasar proximity? What mechanism can keep it so hot?

Finding one WHIM, excluding the Milky Way's, and proposing they (WHIMS) represent half the baryonic mass of the universe seems....(forgive me)...whimsical. Am I too pessimistic?

TravisM
2005-Feb-07, 03:56 PM
The gas is still cooling off. Space itself may only be 2.7K but not the constiuents. 8)

George
2005-Feb-07, 04:02 PM
The gas is still cooling off. Space itself may only be 2.7K but not the constiuents. 8)

Wow. I would not have guessed this. Matter radiates as the 4th power of it's temp. What would have been the gases temp. say 100 million or so years earlier? #-o

ngc3314
2005-Feb-07, 04:14 PM
The gas is still cooling off. Space itself may only be 2.7K but not the constiuents. 8)

Wow. I would not have guessed this. Matter radiates as the 4th power of it's temp. What would have been the gases temp. say 100 million or so years earlier? #-o

Only dense matter (which does approach a theoretical blackbody). At low densities, cooling options are more limited, which is why gas in galaxy clusters stays at 10^7 K for so long. This stuff would be somewhat hotter and cools very inefficiently, since the only cooling available for what are mostly loose protons and electrons happen when they happen to pass close enough together for electromagnetic forces to change their paths. Then they radiate (having charges and being accelerated). But that doesn't happen often at these temperatures.

A sort-of-analogous trick was used to cool the Bose-Einstein condensates for the original Nobel work - use a type of atom which has no absorption lines in the whole wavelength range where the vacuum tank's walls radiate thermally. Then they remain blind to that whole surrounding heat bath. I thought that was unspeakably clever.

George
2005-Feb-07, 07:33 PM
... Matter radiates as the 4th power of it's temp. What would have been the gases temp. say 100 million or so years earlier? #-o
Only dense matter (which does approach a theoretical blackbody). At low densities, cooling options are more limited, which is why gas in galaxy clusters stays at 10^7 K for so long.
Ug. This is counter intuitve for me. I am too familiar with normal matter & temp. The greater the density, the greater the ability to hold heat (assuming a smaller surface to mass ratio compared with less dense regions).

Also, the power from a Planck bb radiation curve is quite significant at the stated temperatures (watts/m^2).


This stuff would be somewhat hotter and cools very inefficiently, since the only cooling available for what are mostly loose protons and electrons happen when they happen to pass close enough together for electromagnetic forces to change their paths. Then they radiate (having charges and being accelerated). But that doesn't happen often at these temperatures.
I think I get it. Are you saying plasma does not release energy as lower temp. matter?


A sort-of-analogous trick was used to cool the Bose-Einstein condensates for the original Nobel work - use a type of atom which has no absorption lines in the whole wavelength range where the vacuum tank's walls radiate thermally. Then they remain blind to that whole surrounding heat bath. I thought that was unspeakably clever.
Wow. I have heard of this but have avoided it's detail. Sounds like inelastic activity is not allowed. I suppose they found bb purity by drilling a hole in the side of the tank wall... :wink: (ok, nevermind :) )

IIRC, recombination was at about 3,000K. If half the matter (baryonic) in the universe is now near 1 million K, is there a good explanation for this increase? (trying to get back on topic :) )

ngc3314
2005-Feb-07, 07:56 PM
... Matter radiates as the 4th power of it's temp. What would have been the gases temp. say 100 million or so years earlier? #-o
Only dense matter (which does approach a theoretical blackbody). At low densities, cooling options are more limited, which is why gas in galaxy clusters stays at 10^7 K for so long.
Ug. This is counter intuitve for me. I am too familiar with normal matter & temp. The greater the density, the greater the ability to hold heat (assuming a smaller surface to mass ratio compared with less dense regions).

Also, the power from a Planck bb radiation curve is quite significant at the stated temperatures (watts/m^2).

Blackbody radiation requires that the matter be able to emit and absorb at essentially all frequencies. Solids manage this by coupling particles into larger structures, and dense enough gases have pressure effects that broaden the reach of individual spectral features. Dilute gases can't manage it - which is why the spectrum of the Orion Nebula is so different from a star's. This also tells why the blackbody nature of the microwave background doesn't just come from the process of recombination, but was set at an earlier epoch when the gas was yet denser (and when continuum radiation processes dominated).




This stuff would be somewhat hotter and cools very inefficiently, since the only cooling available for what are mostly loose protons and electrons happen when they happen to pass close enough together for electromagnetic forces to change their paths. Then they radiate (having charges and being accelerated). But that doesn't happen often at these temperatures.
I think I get it. Are you saying plasma does not release energy as lower temp. matter?




IIRC, recombination was at about 3,000K. If half the matter (baryonic) in the universe is now near 1 million K, is there a good explanation for this increase? (trying to get back on topic :) )

There is, if you allow simulations as good explanations... They predict that most of the energy is originally gravitational, turning into kinetic energy as the gas falls into denser regions over cosmic time. The same thing happens to gas in the overall potential well of a cluster of galaxies, and we're now looking at potentials which are even deeper (but more spread out so you don't have such a tight core). The heating (i.e. conversion into random motions of individual particles) would occur in shock fronts as material falling from different directions interacts (in the collisionless shocks which seem to be an astrophysical specialty). Renyue Cen at Princeton has some simulation visualizations of various phases of intergalactic gas at various cosmic times viewable at http://www.astro.princeton.edu/~cen/PROJECTS/p1/p1.html.

George
2005-Feb-07, 11:26 PM
Blackbody radiation requires that the matter be able to emit and absorb at essentially all frequencies. Solids manage this by coupling particles into larger structures, and dense enough gases have pressure effects that broaden the reach of individual spectral features. Dilute gases can't manage it - which is why the spectrum of the Orion Nebula is so different from a star's.
Thus, if I understand this, a star is closer to a blackbody as it is dense gas, as well as, plasma (for most classes). Are you saying these WHIMs are dense structures with significant pressures?


This also tells why the blackbody nature of the microwave background doesn't just come from the process of recombination, but was set at an earlier epoch when the gas was yet denser (and when continuum radiation processes dominated).

Surprisngly, the CMB power curve actually makes sense to me. However, you may be talking of something else.



IIRC, recombination was at about 3,000K. If half the matter (baryonic) in the universe is now near 1 million K, is there a good explanation for this increase? (trying to get back on topic :) )

There is, if you allow simulations as good explanations... They predict that most of the energy is originally gravitational, turning into kinetic energy as the gas falls into denser regions over cosmic time. The same thing happens to gas in the overall potential well of a cluster of galaxies, and we're now looking at potentials which are even deeper (but more spread out so you don't have such a tight core). The heating (i.e. conversion into random motions of individual particles) would occur in shock fronts as material falling from different directions interacts (in the collisionless shocks which seem to be an astrophysical specialty). Renyue Cen at Princeton has some simulation visualizations of various phases of intergalactic gas at various cosmic times viewable at http://www.astro.princeton.edu/~cen/PROJECTS/p1/p1.html.
Let see if I am getting this....
The primal clouds shrank and became very hot due to their conversion of potential (gravitational) engery to kinetic energy/radiation. Their plasma state allows them to hold their energy for the regions which are dense enough. They exhibit near blackbody radiation, too. (Am I even close?)

What of molecular clouds within galaxies? At 100 K or less, they hold no bragging rights to these WHIMS. Was their fall to each other so much less in energy? I would have guessed the WHIMS would have been as cool as nebulae or cooler, (of course, I would have been wrong, but not surprisingly. :-? ) Is time a greater consideration here? [Most of the baryonic matter in the Orion Nebulae has been around for almost 13.5 billion years.]

[Edit: in regards to your link, looks like Renyue Cen should enjoy Chandra's results.

New, high resolution, large-scale, cosmological hydrodynamic galaxy formation simulations of a standard cold dark matter model (with a cosmological constant) are utilized to predict the distribution of baryons at the present and at moderate redshift. It is found that the average temperature of baryons is an increasing function of time, with most of the baryons at the present time having a temperature in the range 10^{5-7} K. Thus, not only is the universe dominated by dark matter, but more than one half of the normal matter is yet to be detected.

Is this another contribution favoring Big Bang theory?

ngc3314
2005-Feb-08, 02:09 PM
IIRC, recombination was at about 3,000K. If half the matter (baryonic) in the universe is now near 1 million K, is there a good explanation for this increase? (trying to get back on topic :) )

There is, if you allow simulations as good explanations... They predict that most of the energy is originally gravitational, turning into kinetic energy as the gas falls into denser regions over cosmic time. The same thing happens to gas in the overall potential well of a cluster of galaxies, and we're now looking at potentials which are even deeper (but more spread out so you don't have such a tight core). The heating (i.e. conversion into random motions of individual particles) would occur in shock fronts as material falling from different directions interacts (in the collisionless shocks which seem to be an astrophysical specialty). Renyue Cen at Princeton has some simulation visualizations of various phases of intergalactic gas at various cosmic times viewable at http://www.astro.princeton.edu/~cen/PROJECTS/p1/p1.html.
Let see if I am getting this....
The primal clouds shrank and became very hot due to their conversion of potential (gravitational) engery to kinetic energy/radiation. Their plasma state allows them to hold their energy for the regions which are dense enough. They exhibit near blackbody radiation, too. (Am I even close?)


They ought to give off very feeble hard X-ray continuum from brehmsstrahlung, which has yet to be detected. What's been seen so far is absorption again bright background sources of deep UV and X-ray radiation; this absorption includes oxygen ionized 5 and more times, the relative amounts of the ionization states giving a temperature estimate.


What of molecular clouds within galaxies? At 100 K or less, they hold no bragging rights to these WHIMS. Was their fall to each other so much less in energy? I would have guessed the WHIMS would have been as cool as nebulae or cooler, (of course, I would have been wrong, but not surprisingly. :-? ) Is time a greater consideration here? [Most of the baryonic matter in the Orion Nebulae has been around for almost 13.5 billion years.]



The cooling processes that operate in material, and their rates, change dramatically with temperature and density. A dominant issue is the particle density - most processes important in the interstellar and intergalactic media are two-body collisional processes, so their rate scales with the square of the density. On top of that, the state of the matter changes what particular collisional processes operate (embodied in the so-called cooling function). At high temperatures where everything is fully ionized, cooling happens (not all that fast) by brehmsstrahlung, or free-free transitions in which energy is radiated during close passages betwen charged particles. At 10^6 K or so, heavy atoms (Fe, O...) start to hang on to their inner-shell electrons, adding the possibility of being excited to hjgher energy levels by collisions and radiating the energy in X-ray lines. At yet lower temperatures, atoms are only mildly ionized or neutral (10^4 K), and can radiate collisionally-gained energy very effectively. Then at cold levels (100 K), molecular transitions in the mm range and thermal emission from dust grains are most important. Cooling material will "stick" longest at temperatures where it cools least effectively (hence the WHIM). Cooling at low temperatures is highly dependent on the abundance of heavy elements (which is why the first generation of stars is thought to have been so massive - less massive lumps could not form because the stuff didn't cool rapidly enough to shrink below thousand-solar-mass clouds).

Additional issues come in for the ISM in our galaxy - we see a snapshot of a very dynamic history, constantly cycling among various phases. The high density in galaxies makes things go fast compared to the intergalactic boonies.

George
2005-Feb-08, 02:47 PM
What of molecular clouds within galaxies? At 100 K or less, they hold no bragging rights to these WHIMS. Was their fall to each other so much less in energy? I would have guessed the WHIMS would have been as cool as nebulae or cooler, (of course, I would have been wrong, but not surprisingly. :-? ) Is time a greater consideration here? [Most of the baryonic matter in the Orion Nebulae has been around for almost 13.5 billion years.]
... At high temperatures where everything is fully ionized, cooling happens (not all that fast) by brehmsstrahlung, or free-free transitions in which energy is radiated during close passages betwen charged particles. At 10^6 K or so, heavy atoms (Fe, O...) start to hang on to their inner-shell electrons, adding the possibility of being excited to hjgher energy levels by collisions and radiating the energy in X-ray lines. At yet lower temperatures, atoms are only mildly ionized or neutral (10^4 K), and can radiate collisionally-gained energy very effectively. Then at cold levels (100 K), molecular transitions in the mm range and thermal emission from dust grains are most important. Cooling material will "stick" longest at temperatures where it cools least effectively (hence the WHIM).
Can I say the heavier elements are more readily able to hold electrons which will allow greater photon emission and greater cooling?

Is Planck's bb curve erroneous for WHIMs and hot non-metalic clouds (since cooling/radiation seems so different)?


Cooling at low temperatures is highly dependent on the abundance of heavy elements (which is why the first generation of stars is thought to have been so massive - less massive lumps could not form because the stuff didn't cool rapidly enough to shrink below thousand-solar-mass clouds).
I think I see...The early h/he clouds maintened their energy so the net cloud pressure attenuated gravitational collapse compared with today's more metalic clouds. Right?

Will h & he avoid much of the gravitational collapse in today's clouds as the metalic elements condense?

[BTW, I appreciate your help with this. If I don't ask further questions, it's to avoid feeling guilty for not paying you. :) ]

ngc3314
2005-Feb-08, 06:18 PM
Can I say the heavier elements are more readily able to hold electrons which will allow greater photon emission and greater cooling?


Pretty much. More electrons, and electrons in energy levels that can be excited at various temperature ranges.



Is Planck's bb curve erroneous for WHIMs and hot non-metalic clouds (since cooling/radiation seems so different)?


Cooling at low temperatures is highly dependent on the abundance of heavy elements (which is why the first generation of stars is thought to have been so massive - less massive lumps could not form because the stuff didn't cool rapidly enough to shrink below thousand-solar-mass clouds).
I think I see...The early h/he clouds maintened their energy so the net cloud pressure attenuated gravitational collapse compared with today's more metalic clouds. Right?

Will h & he avoid much of the gravitational collapse in today's clouds as the metalic elements condense?

Early on, indeed the H/He gas would stay hotter, and therefore would not collapse as far under gravity as would higher-metallicity gas later on, so the smallest lumps that would become compact enough to ignite H fusion would be much larger than the norm today (hence the discussion about massive first-generation stars).

Today, various elements are usually well enough mixed (and in ionized gas, electromagnetically entangled) to all follow the dictates of gravity.
Unless you look at the atmosphere of something with the gravitational acceleration of a white dwarf. The only nebular exceptions that come to mind happen when the gas started out chemically stratified and has not yet had time to undo that - as in planetary nebulae, sort of a red giant peeled open, and supernova remnants, where you may see very metal-rich "bullets" moving at high speed from the inner part of the progenitor.
(Surely this constitutes thread drift!)



[BTW, I appreciate your help with this. If I don't ask further questions, it's to avoid feeling guilty for not paying you. :) ]

No, don't feel guilt over not paying me. There are some organizations out there with contractual arrangements who seem to feel no guilt over not paying me, or at least not for months and months... and I had a long chat with a ballroom-dance band leader about why the trombonist deserves to be paid the same as the sax and trumpet players. :(

George
2005-Feb-08, 11:35 PM
Early on, indeed the H/He gas would stay hotter, and therefore would not collapse as far under gravity as would higher-metallicity gas later on, so the smallest lumps that would become compact enough to ignite H fusion would be much larger than the norm today (hence the discussion about massive first-generation stars).

I'm curious if there is a time frame astronomers assign this period. First 5 billion years or is it less since the Big Blue's burn so fast and add metals rapidly?


Today, various elements are usually well enough mixed (and in ionized gas, electromagnetically entangled) to all follow the dictates of gravity.
Unless you look at the atmosphere of something with the gravitational acceleration of a white dwarf. The only nebular exceptions that come to mind happen when the gas started out chemically stratified and has not yet had time to undo that - as in planetary nebulae, sort of a red giant peeled open, and supernova remnants, where you may see very metal-rich "bullets" moving at high speed from the inner part of the progenitor.
Hence the green colored nebula tendrils (ionized oxygen) and others, I think. [ I still am considering the colorscope idea to see these guys. The Sun's color comes first, of course :) ]


(Surely this constitutes thread drift!)


Possibly, but WHIMs are clouds.

[quote="ngc3314"][quote="George"][BTW, I appreciate your help with this. If I don't ask further questions, it's to avoid feeling guilty for not paying you. :) ]
No, don't feel guilt over not paying me. There are some organizations out there with contractual arrangements who seem to feel no guilt over not paying me, or at least not for months and months...
I could start an entire forum on the subject of not getting paid. :-?


and I had a long chat with a ballroom-dance band leader about why the trombonist deserves to be paid the same as the sax and trumpet players. :(
Just ask the trombonist. :)

ngc3314
2005-Feb-09, 01:34 AM
Early on, indeed the H/He gas would stay hotter, and therefore would not collapse as far under gravity as would higher-metallicity gas later on, so the smallest lumps that would become compact enough to ignite H fusion would be much larger than the norm today (hence the discussion about massive first-generation stars).

I'm curious if there is a time frame astronomers assign this period. First 5 billion years or is it less since the Big Blue's burn so fast and add metals rapidly?




Not that long. "Normal" star formation could only get started once the BBS (Big Blue Superstars, not to be confused with Big Blue itself or Bulletin Board Services) had lived and died, enriching the gas most everywhere. We now see their presumed chemical results to within about 800 Myr from time zero, so people figure maybe within 0.5 Gyr. It would be very reassuring to see their superdupernovae with JWST.





and I had a long chat with a ballroom-dance band leader about why the trombonist deserves to be paid the same as the sax and trumpet players. :(
Just ask the trombonist. :)
Oh, yeah, don't get me started. At least he finally lets me take an occasional lead verse on something besides "Getting Sentimental Over You". Thought he was being funny handing me "Fly Me to the Moon" and "Stars Fell on Alabama". Next stop would be "Stardust" and "Blue Moon", I suppose.

George
2005-Feb-09, 05:04 AM
It would be very reassuring to see their superdupernovae with JWST.
Time will tell. That's a lot of redshift. :)




and I had a long chat with a ballroom-dance band leader about why the trombonist deserves to be paid the same as the sax and trumpet players. :(
Just ask the trombonist. :)
Oh, yeah, don't get me started. At least he finally lets me take an occasional lead verse on something besides "Getting Sentimental Over You". Thought he was being funny handing me "Fly Me to the Moon" and "Stars Fell on Alabama". Next stop would be "Stardust" and "Blue Moon", I suppose.
It all sounds cool to me. If Glen Miller can accomplish so much with clarinets, why not? I am biased on the trumpet, however, since I played it into high school. Switched to guitar. Trumpet wasn't loud enough. :lol:

Btw, you get in the mood to discuss accretion disks, just fire-up a thread and I'll be there. 8)