[Democritus (OP)]

Folks,
Rather than contribute further to a weary debate, I thought I would offer some brand new good news.. here:

http://www.monash.edu.au/news/show/monash-student-finds-universes-missing-mass
 
Thought that might grab a little attention..
Sincerely
Democritus

[imatfaal]

Folks,
Rather than contribute further to a weary debate, I thought I would offer some brand new good news.. here:

http://www.monash.edu.au/news/show/monash-student-finds-universes-missing-mass
 
Thought that might grab a little attention..
Sincerely
Democritus

Might have been better to make a different thread - would you mind if we split it off to make a new thread?

[Democritus (OP)]

Dear Imatfaal
Yes, of course I welcome a new thread here if you wish.
While I'm not sure how to do it so as to include the link to Monash and the 'sub-link' therein to the original paper..(now there's a little mathematics required to help our understanding of the physics of the universe..), I'm hopeful you or your colleagues can.
Best wishes & sincerely
Democritus

[imatfaal]

Democritus - good find! 

Yeah this is a pretty damn good result for a 22 year student.  She seems to have confirmed by remarkable observation and experiment some of answers to dark/hidden matter than were previously theorised.  This missing mass she has found, if I have read correctly, is some of the dark baryonic matter.  ie it's normal particles that we understand - but it wasn't included in observational data.  the bigger question is what is the non-baryonic matter?  But even so - for an undergrad, great work!

Steve Nerlich commented as follows

The universe recipe of 74% dark energy, 22% dark matter and 4% baryonic is unchanged. It's just that Bregman predicted that a lot of the baryonic matter would be in the form of Warm-Hot Intergalactic Medium (WHIM) - or filaments. This appears to be confirmed now, so good science all round.

Bregmans theoretical paper is here http://arxiv.org/PS_cache/arxiv/pdf/0706/0706.1787v1.pdf

Amelia Fraser-McKelvie’s preprint is here http://arxiv.org/abs/1104.0711

[yor_on]

"“It was thought from a theoretical viewpoint that there should be about double the amount of matter in the local Universe compared to what was observed.  It was predicted that the majority of this missing mass should be located in large-scale cosmic structures called filaments - a bit like thick shoelaces,” said Dr Pimbblet. 

Astrophysicists also predicted that the mass would be low in density, but high in temperature - approximately one million degrees Celsius. This meant that, in theory, the matter should have been observable at X-ray wavelengths. Amelia Fraser-McKelvie’s discovery has proved that prediction correct.""

This doesn't sound as the definitions I've seen of dark matter? It has a temperature and so seems to act as normal baryonic matter?

This is the definition from NASA.

"We are much more certain what dark matter is not than we are what it is. First, it is dark, meaning that it is not in the form of stars and planets that we see. Observations show that there is far too little visible matter in the Universe to make up the 25% required by the observations.

Second, it is not in the form of dark clouds of normal matter, matter made up of particles called baryons. We know this because we would be able to detect baryonic clouds by their absorption of radiation passing through them.

Third, dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter annihilates with matter. Finally, we can rule out large galaxy-sized black holes on the basis of how many gravitational lenses we see. High concentrations of matter bend light passing near them from objects further away, but we do not see enough lensing events to suggest that such objects to make up the required 25% dark matter contribution.""

[imatfaal]

Hi Yor_on - Mea Culpa (i made title when splitting thread) yeah missing matter is a better title.  i made this point in the text but forgot to do it in the title.  So many of the pop-sci articles referred to it as dark matter it stuck in my brain. 

It is normal baryonic matter - it's just that 90pct of the baryonic matter predicted by bingbang nucleosynthesis is not in galaxies and groups; this was another part of the search to cut down the missing portion.

[yor_on]

Well Imatfaal, I'm sort of confused reading it too
Missing matter, but predicted? Or missing matter that wasn't predicted?

And the way it was formulated made me have to recheck my understanding of what dark matter was expected to be.
=

Rethinking I believe it to be part of the ordinary matter we always expected to exist, although we didn't know where, sort of.

[imatfaal]

Your last line sums it up.  If the big bang is correct then the levels of nucleosynthesis predict an amount of baryonic matter - but we could only see and account for a small fraction of this.  Theorists had predicted a good lump would be in the filaments and this has shown this to be the case

[CliffordK]

I think the news release exaggerates the role of the undergrad in the discovery.

When you follow the links included in the release to find the article:
http://arxiv.org/abs/1104.0711

with links to the PDF in full.

You find that the filaments were discovered and cataloged in previous research, and this research was merely to characterized previously known filaments.

It sounds like interesting stuff though.

Very low density (gas/vapor?) in the middle of space, at very high temperatures, with the background temperature of space supposed to be around 4K.  But, perhaps there is no true temperature in a vacuum and gases in a vacuum behave differently than solid matter.