[iheartmemcache]

Dang I read the first paragraph of the article and immediately went searching for the real papers since I didn't expect any media outlet to include them at the bottom, but here they are for anyone who made the same mistake I did! https://arxiv.org/abs/1709.05024 https://arxiv.org/abs/1709.10378

Not a cosmologist but here's my go at the de Graff paper. (Let's get this out of the way, the title is click-bait and the paper/researchers makes no such claims as to anything near 50%. New Scientist is trolling for hits with the word "half" or the journalist is fundamentally misunderstanding the work.) In de Graff, et al, they claim 30% of "90% of the missing baryonic matter [that composes the ~25% of our total universe observable from within our light cone]" has been found in the CMB structured as filaments between galaxies. They claim there's effectively a planar network layered on top of Minkowski space composed this baryonic matter. The temperature was at this "Goldilocks" midrange no one had previously analyzed (ranging from 10^5-10^7K). This wasn't previously found because people were searching "only the lower and higher temperature end of the warm-hot baryons, leaving the majority of the baryons still unobserved(9)". [See "Warm-hot baryons comprise 5-10 percent of filaments in the cosmic web.", Nature, Eckert et al for more about baryons of this composition.]

Additionally, these baryons have 10x the density of what we observe (so this could potentially be evidence for the first stable baryonic matter composed of second generation quarks, or more likely the binding energies are different from our standard uud/udd nucleon quarks) permeating the universe, and where the roads in the network meet ("dark matter haloes"), you have embedded galaxies and galaxy clusters. They continue with their analytic methods of the CMASS data, and claim within the framework 30% of the total baryonic content (which, again, all analytical methods put this into no more than ~25%) is composed of this form of this matter. I skimmed their methods and it seemed to at least logically hold -- they are using the appropriate data (SDSS 12) and didn't cherry-pick their galaxy pairs (so, no p-hacking here!).

[DiabloD3]

From what I can tell, this basically also proves that large scale plasma exists between all bodies at any scale (planetary to systems to galaxies to clusters), and universe sized Birkeland currents exist; which is something cosmologists have been trying to prove/disprove for awhile.

So, not only did they find some of the missing matter, they found some of the missing energy, too. This does, however, screw some of the more classical cosmologists.

[nolta]

> So, not only did they find some of the missing matter, they found some of the missing energy, too.

Nope, this has nothing to do with dark energy.

> This does, however, screw some of the more classical cosmologists.

Not sure who you're referring to. These results are completely consistent with the standard model of cosmology.

[ab5tract]

> Not sure who you're referring to. These results are completely consistent with the standard model of cosmology.

Not if what is being detected is simply mass associated with filamentary currents of energy (with attendant magnetic fields) rather than particular particles.

[nolta]

They're modelling filaments as cylindrical tubes of hot electrons connecting pairs of galaxies. I don't know what you mean by "mass associated with filamentary currents of energy", but while the electrons are hot (~million Kelvin), they're non-relativistic and their kinetic energy is negligible.

[nolta]

> Additionally, these baryons have 10x the density of what we observe (so this could potentially be evidence for the first stable baryonic matter composed of second generation quarks, or more likely the binding energies are different from our standard uud/udd nucleon quarks)

No, these results are not evidence for exotic matter. They measured the over-density of the filaments relative to the average background density of the universe.

[vanderZwan]

> Let's get this out of the way, the title is click-bait and the paper/researchers makes no such claims as to anything near 50%. New Scientist is trolling for hits with the word "half" or the journalist is fundamentally misunderstanding the work.

At first I agreed with you, but I've dug into the articles and re-read the New Scientist article too to make sure, and it seems the story is a bit more complicated than it at first appears (caveat: I'm also not a cosmologist). They should have clarified this research does not involve dark matter though.

Part of the confusion stems from losing context and awareness of implicit limits to the claims when translating exact cosmological terms to popular science. "Baryonic matter" means nothing to the average person, and calling it "observable matter" could also be confusing to lay-people, since this matter isn't actually directly observable:

> “There’s no sweet spot – no sweet instrument that we’ve invented yet that can directly observe this gas,” says Richard Ellis at University College London. “It’s been purely speculation until now.”

However, the researchers do seem to claim they solved the mystery of the missing observable matter by detecting gas filaments:

> “The missing baryon problem is solved,” says Hideki Tanimura at the Institute of Space Astrophysics in Orsay, France, leader of one of the groups. The other team was led by Anna de Graaff at the University of Edinburgh, UK.

Whether that can should be translated as "finding the missing 50% of observable matter" depends on whether those baryons are in fact 50% of missing observable matter. To make things more confusing for non-cosmologists here, the two papers tell slightly different stories, because they don't do the exact same thing. De Graaff's paper mentions a much lower number than 50%, as you stated, but the introduction of Tanimura mentions:

> At high redshift (z ≳ 2), most of the expected baryons are found in the Lyα absorption forest: the diffuse, photo-ionized in- tergalactic medium (IGM) with a temperature of 10⁴ – 10⁵ K (e.g., Weinberg et al. 1997; Rauch et al. 1997). However, at redshifts z ≲ 2, the observed baryons in stars, the cold interstellar medium, residual Lyα forest gas, OVI and BLA absorbers, and hot gas in clusters of galaxies account for only ∼50% of the expected baryons – the remainder has yet to be identified (e.g., Fukugita & Peebles 2004; Nicastro et al. 2008; Shull et al. 2012). Hydrodynamical simulations suggest that 40–50% of baryons could be in the form of shock-heated gas in a cosmic web between clusters of galaxies.

It looks like this is where that half in the New Scientist title comes from: 40-50% of missing baryons should be in these gas filaments. This might appear to contradict De Graaf et al., but the latter mention Tanimura et al. in the conclusions of their paper:

> Similar conclusions to this work have been independently drawn by Tanimura et al. (...) who announced their analysis (...) at the same time as this publication. (my summary: We used different, independent but complementary galaxy pair catalogues). Despite the differences, we achieved similar results in terms of the amplitudes and statistical significances of the filament signal. (...) The fact that two independent studies using two different catalogues achieve similar conclusions provides strong evidence for the detection of gas filaments.

So given that these two groups seem to be in agreement with each other's conclusions, and that Tanimura himself was quoted (so presumably consulted for the article), it seems that the main clickbait aspect of the New Scientist article is that they did not clarify that no dark matter is involved in this story.

[ChuckMcM]

And the combination of your observation and DiabloD3's is an interesting one. The papers on Birkeland currents in the context of a galaxy spanning plasma makes for some fun conjecturing. A coulomb of charge moving in a million light year long filament of plasma is lot of energy.

[CodeTheInternet]

> https://arxiv.org/abs/1709.10378

Mmhmm, yes, I know some of these words!