Missing Mass Discovered

[renormalised (Carl)]

Originally Posted by CraigS

I have a feeling this defines the term 'missing'. In a nutshell, it was predicted, but not found. It was thus 'missing'. Amelia et al are on the path of finding it.

Cheers

It's the same as saying overlooked. It wasn't literally missing and not, therefore, a part of what was there. They can find it, however, they need to change their methods to do so, or look at old data with different and new "eyes". That's what Amelia did and she found the "missing" mass.

Truly missing mass would equate to what we call DM. You can barely detect it (and then only because of its gravity) and it just doesn't interact with anything ordinary. You can't see it or detect it in any ordinary sense of the definition. So, it becomes literally missing...nowhere to be seen but it's there because everything else is doing this or that because of its presence.

[CraigS]

Carl;
Thanks for your post #60.

Other than involving theoretical explanations, I still don't see how they can differentiate spectroscopically, between ionised gas filaments detected at X-ray wavelengths via thermal bremmstrahlung emissions (smooth continuous spectrum)…. and an ionised plasma in a BC (smooth, continuous spectrum).

They mention they can also look at observations at 0.65 keV O line in absorption or emission, but these may also appear in a BC plasma (?)

The difference between the two is the charge separation, but how can this be remotely differentiated from an ionised plasma, if the plasma isn't emitting any other EM radiation at different wavelengths ?

Cheers

[renormalised (Carl)]

The wavelength of the emitted radiation is an indicator of the mechanisms which produce it. BC's produce visible light and radio noise only because they don't have any electrons which are relativistic in nature. Xrays produced via thermal bremmstrahlung need relativistic electrons to be produced. Anything with gamma radiation needs relativistic electrons (or other relativistic particles, e.g. photons) in this situation (ionised plasmas) to be produced. They'll also produce light and radio waves as well. Same with synchrotron radiation....electrons spiraling in a magnetic field and accelerated to relativistic velocities. Basically a Bennett Pinch and not a BC.

[CraigS]

After much reading, I think I'm now getting a much better understanding of how all this fits together ….

The Big Bang/Lambda CDM Theory says that following the Reionisation Epoch (near z~6), (by which time, most of the intergalactic medium had been photoionised to a temperature of about 10^4K), the predominant heating mechanism was through thermal shocks that developed as large-scale density waves collapsed in the dark matter. This pushed the temperature up to the 10^5K region in the volume for z<1. Systems and galaxies develop with temperatures of 10^7 to 10^8K, which can be observed by X-Ray telescopes.

So, what was predicted by the Big Bang/Lambda CDM model, was that these 'WHIM' filaments may be detected at X-ray wavelengths at a volume of z<1, and would be produced by thermal bremmstrahlung emission.

So what they've now observed is:

- soft X-Ray emissions in two energy bands: 0.9-1.3 keV and 0.5-2.0 keV. ('Soft' X-Ray emission is from about 0.12 keV to 12 keV).

- the thermal temperature range predicted by theory, translates to 0.0086-0.86 keV (10^5 to 10^7 K), so what they've detected falls (somehwhat) within these bands.

The thermal bremmstrahlung radiation is given off by electrons, as they are scattered by the strong electric field near the other high speed nuclei (ionised) in the filaments. These X-rays have a continuous spectrum. So, this is the source of the X-Ray emissions.

Now, I personally think that the term 'Birkeland currents' is hugely generalised and not particulary well-defined. The spectral emission energies in Earth's Auroras, can range anywhere from 1 to 200 keV, which still overlaps with what Amelia et al have detected. (As avery rough example of a well-known Birkeland Current phenomenon).

As such, it appears that the only reasons I can find, to rule out that what Amelia et al have observed may be a 'Birkeland Current', is a well-defined, empircally plausible, cause mechanism (ie: some evidence of a huge, self-sustaining intergalactic battery at either end of the filaments, to create the initial current flow in the filament). The self-sustaining mechanism which ensues, requires charge separation to be maintained continuously in the filament and it is a complete mystery as to how this can happen, unless energy is continuously added to the filament. If reconnection conditions occur, energy would be lost, and distinctive emissions would be able to be detected. So where could this big-battery possibly come from ? .. all sorts of story-telling then ensues, with little/no specific observational evidence, for the case in hand .. ie: for example, take the filament from Abell 2829 to Abell 0118 .. ~ 20 Mpc in length ? Are Abell 2829 and Abell 0118 somehow able to act together as a giant anode/cathode pair ?

The BB/Lambda CDM model on the other hand, defines a cause mechanism and made the prediction, and Amelia et al found the smokin' gun !

That's my take on it all.

Has anyone ever seen any papers which classify the spectra of Birkeland Currents having typical space-bound plasma environments ? (This information may help to differentiate a BC from an ionic gas plasma filament, at least spectroscopically).

Cheers

[renormalised (Carl)]

Craig...don't give the EU guys a smell of the oily rag, mate

They'll jump at those suggestions and run with them like they're pots of gold at the end of the EU rainbow

They'll start looking for the giant "Energiser" AA cells in space, next

Or the Energiser Bunny (although they probably see him anyway)

I haven't seen any papers offhand, but I would imagine there are some.

However, if you have some sort of "battery in space", it's like I said in a previous post....it's going to be very obvious observationally. You would have to have a +ve and -ve charge end to the filaments and that's not what is seen. Not only that, the polarities would have to be self sustaining over enormous periods of time and you have to invoke a mechanism that can enact that charge separation. I can't think of anything astrophysical that could do that. Not anything that immediately comes to mind.

[sjastro]

They mention they can also look at observations at 0.65 keV O line in absorption or emission, but these may also appear in a BC plasma (?)

Hi Craig,

Is this supposed to be a absorption/emission line for a BC?

If you can confirm this then it is may be possible to differentiate between a plasma (or a gas with a low ionization content) and a BC.
A BC current is a magnetic field aligned current hence it is possible for the emission/absorption line in the spectrum to split in the presence of the magnetic field.

http://en.wikipedia.org/wiki/Zeeman_effect

This of course assumes the plasma or low ionization gas is not in an external magnetic field.

Regards

Steven

[CraigS]

Originally Posted by sjastro

Hi Craig,

Is this supposed to be a absorption/emission line for a BC?

If you can confirm this then it is may be possible to differentiate between a plasma (or a gas with a low ionization content) and a BC.
A BC current is a magnetic field aligned current hence it is possible for the emission/absorption line in the spectrum to split in the presence of the magnetic field.

http://en.wikipedia.org/wiki/Zeeman_effect

This of course assumes the plasma or low ionization gas is not in an external magnetic field.

Regards

Steven

Hi Steven;
Unfortunately, my wording was an artifact from my grappling/questioning whether a BC and the filaments observed may be detected using similar means.

The 0.65 keV absorption/emission referred to in Amelia's paper, was alluding to one of the means her predecessors have attempted to use to detect these filaments.

Whilst exploring in the UV region, they have previously attempted to use OVI and HI Ly alpha lines as a possible probe of gases in the near to 3x10^5 K temperature region. Beyond 3x10^5K, these lines are of little use, and X-Ray lines become more important. Apparently, due to the absorption by neutral gas in the Milky Way, there is a natural divide between the UV and X-Ray regions. The UV region ends at 13.6eV and the X-Ray region becomes more useful above 200 eV.

Hydrogenic oxygen (OVIII), absorption, has an equivalent Ly alpha line at 654 ev. I think this is what Amelia was referring to.

I found a great paper on all this (from where the above info is sourced).
Page #5: "Section 3: Atomic Physics", talks about the 'ins and outs' of the physics side of it.

It'd be great if you could have a squizz at it.

I'd like to take a punt, and say that if these lines appeared in the spectrum of any filament, and were found to be split, courtesy of the Zeeman effect, then that could be used to infer a Strong Magnetic Field … boom … presto .. there's ya BC!

If not, why not ?
Great idea !



Cheers

[Mike21 (Michael)]

This conversation is way over my head but I thought youse might like this.

http://www.abc.net.au/news/stories/2....htm?site=news

[CraigS]

There appears to be quite a few other ways these guys have developed to detect these ultra-thin (density-wise) filaments, all having their strengths and weaknesses:

- X-Ray and UV absorption lines (primary tool);
- X-Ray emission (inside and near Galaxy Clusters .. note!);
- soft excess emission within the virial radius of galaxy clusters;
- the absence of OVI emission;
- OVII and OVIII emission;
- looking for shadows in the X-Ray spectrum caused by X-Ray opaque clouds against a background emission by a filament;
- dispersion: (ionized plasma has a frequency-dependent index of refraction, which produces a measurable effect at radio wavelengths) - Interesting !!
- radio 'hyperfine' lines and;
- the Sunyaev-Zeldovich Effect.

So, at the end of the day, interstellar ionised gas filaments CAN be detected and it appears that 41 bona-fide inter-cluster filaments have been detected and catalogued to date.

It may be possible to distinguish (spectroscopically) a 'filament' from a hypothesised inter-cluster 'Birkeland Current' (BC), depending on its energy level, (ie: its state of excitement/state of discharge). This would be (perhaps) done, depending on the strength of its magnetic field, via the Zeeman Effect ... although, this is subject to other possible causes, which would have to be ruled out by other evidence/arguments.

The X-Ray emission mechanism from the filaments detected, is stated by Amelia's paper, as being caused by thermal bremsstrahlung radiation. This is also what would be, (presumably), expected to emitted by a BC in the latter stages of 'dark mode', probably in 'glow mode' and surely in 'arc' mode (a synchrotron radiation spectrum would also be expected in 'arc' mode (??)).

That about sums it up for me. None of the (lots) of papers I've read on this mention anything about the filaments being current-carrying BCs (not surprisingly, I suppose).

There is much discussion about whether the gas filaments are infalling/ejected from the clusters themselves. The cause of the filament X-Rays, seems to have a plausible explanation in the BB/Lambda CDM Standard Cosmological Theory sequence (post re-ionisation epoch at redshift ~6), where shock mechanisms imparted the thermal energies needed for X-Ray emission (at redshifts < 1).

Cheers