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Help with a (seeming) discrepancy?


Baby Astronaut
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In the first paragraph below, the description's indicative of less heat (coldness of a void). Yet in the second and third paragraphs, the description's more indicative of a rise in heat. But isn't each a description of the same place, thus contradictory?

 

http://en.wikipedia.org/wiki/Intergalactic_medium#Intergalactic

 

Generally free of dust and debris, intergalactic space is very close to a total vacuum. Certainly, the space between galaxy clusters, called the voids, is nearly empty. Some theories put the average density of the universe as the equivalent of one hydrogen atom per cubic meter.[22][23] The density of the universe, however, is clearly not uniform; it ranges from relatively high density in galaxies (including very high density in structures within galaxies, such as planets, stars, and black holes) to conditions in vast voids that have much lower density than the universe's average.

 

Surrounding and stretching between galaxies, there is a rarefied plasma[24][25] that is thought to possess a cosmic filamentary structure[26] and that is slightly denser than the average density in the universe. This material is called the intergalactic medium (IGM) and is mostly ionized hydrogen, i.e. a plasma consisting of equal numbers of electrons and protons. The IGM is thought to exist at a density of 10 to 100 times the average density of the universe (10 to 100 hydrogen atoms per cubic meter). It reaches densities as high as 1000 times the average density of the universe in rich clusters of galaxies.

 

The reason the IGM is thought to be mostly ionized gas is that its temperature is thought to be quite high by terrestrial standards (though some parts of it are only "warm" by astrophysical standards). As gas falls into the Intergalactic Medium from the voids, it heats up to temperatures of 105 K to 107 K, which is high enough for the bound electrons to escape from the hydrogen nuclei upon collisions. At these temperatures, it is called the Warm-Hot Intergalactic Medium (WHIM). Computer simulations indicate that on the order of half the atomic matter in the universe might exist in this warm-hot, rarefied state.

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I don't understand this very well but does this suggest that intergallactic space is more dense than space within a galaxy?

 

Also I recall that estimates of the density of matter in the middle of the great voids between superclusters was about one atom per cubic meter. Could it be that the average density of matter in the entire universe, including all stars, black holes, planets, etc, is approximately the same as the average density in the middle of the great voids? And the reason being is that space is so vast, that no matter how much matter there is, the average density of the entire universe is insignificantly greater than the density of empty intergallactic space? :confused:

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...Certainly, the space between galaxy clusters, called the voids, is nearly empty...

Surrounding and stretching between galaxies, there is a rarefied plasma[24][25] that is thought to possess a cosmic filamentary structure[26] and that is slightly denser than the [edit: voids]. This material is called the intergalactic medium (IGM) and is mostly ionized hydrogen, i.e. a plasma consisting of equal numbers of electrons and protons. The IGM is thought to exist at a density of 10 to 100 times the average density of the [edit: voids].

... As gas falls into the Intergalactic Medium from the voids, it heats up to temperatures of 10^5 K to 10^7 K,...

 

I don't think there is a discrepancy, more like an ambiguity in wording. I edited to make it clear that the IGM filamentary structure has a higher density than the voids.

 

Filamentary structure means the cobwebby structure that you may have seen pictures of. If you haven't, then google

"Smoot TED"

for a wonderful 15 minute talk about the filamentary structure and how it formed. There are computer animations that show it forming.

 

The cobwebs include clusters of galaxies and stretch between neighboring clusters. The structure can actually be observed.

 

Things started out more evenly distributed but whereever there was a slight overdensity that would cause surrounding matter to fall towards it.

So you get huge structures of overdensity stretching thru regions of underdensity (relative voids) and the stuff in the comparative voids is always falling like hail down into the comparative condensed cobwebby structures.

 

So it heats up by falling, gains speed, particles collide. Atoms ionize due to collisions.

 

The filaments are still quite un-dense by our standards:D. But they are significantly denser than the voids.

 

At scattered points in those filaments, especially where two filaments cross, you get more condensation. Clusters of galaxies begin to form at crossing points and at other scattered points.

 

We still aren't down to the level of individual galaxies like the Milky Way or like Andromeda. Individual galaxies tend to form in groups, various size clusters. So the key thing we are looking at are the clusters (which people map, and then they see the filamentary structure sort of outlined by the clusters of galaxies.)

 

TED is an organization that puts on lectures. George Smoot is a nobel cosmologist. If you google "Smoot TED" you will get this:

It's online video of a great talk. I think anybody interested in the structure of the universe should check it out.

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TED is an organization that puts on lectures. George Smoot is a nobel cosmologist. If you google "Smoot TED" you will get this:

It's online video of a great talk. I think anybody interested in the structure of the universe should check it out.

Following up on where the above video left off, review for yourself the work being done with the Planck mission.

 

http://www.esa.int/SPECIALS/Planck/index.html

 

 

FIRST_LIGHT_SURVEY_L.jpg

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Martin, I had seen the TED video earlier in the year but it was nice to view it again. The way they moved from great scales to the ones we're more used to is neat. But something's off with his diagram of all the various universe epochs pieced together.

 

He mentioned projects like the galaxy redshift survey. Does it take into account the movements each galaxy (and/or cluster) long after their photons have reached us and where those galaxies would be now?

 

Since all the galaxies we've viewed are in far different positions today (as each galaxy's light reaching us is a snapshot of its distant past), wouldn't the filament shapes be an illusion created by piecing together the different epochs?

 

A bit perhaps like amoebas taking snapshots individually of cars in a human-scale racetrack, and then (in an image) placing each car according to its position when the camera took its picture -- in order to see who's in the lead -- rather than placing each car according to mathematical predictions of where it'd likely be.

 

Earlier this year I brought a similar matter up in another thread: Mapping the universe in "real time"?

 

It's possible I'm wrong and they've mostly accounted for changes in position when making the filaments diagram. I just wrote George Smoot an email to find out more. Below is a part of it...

 

 

I watched your Ted video on galaxy filaments and was interested in how you pieced together all the epochs into a visual whole.

 

A question: is the pieced-together diagram a visual representation of the universe "as is"? i.e. how it looks at this very moment. Because I can't help wonder how different that universe diagram would look after repositioning the older galaxies to their actual positions millions and billions of years later (i.e. today). Would the filaments retain their shape afterward?

 

 

 

oh and iNow, great link.

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  • 4 weeks later...
...

It's possible I'm wrong and they've mostly accounted for changes in position when making the filaments diagram....

 

...their actual positions millions and billions of years later (i.e. today). Would the filaments retain their shape afterward?[/i]

...

 

To the extent possible differences in position are already accounted for. The filamentary structure is observed.

 

It was intelligent of you to think that you might have been wrong in supposing that radial distances had not been brought up to date. You must have used the Ned Wright calculator. If you plug in an observed redshift it calculates the today distance for you.

That's the whole point. If you haven't played around with the cosmo calculator, you should spend some time doing that and get used to it.

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