Rev. Cheeseman said:
Using AI, it said[Redacted by the Mentors -- AI is not a valid reference at PF]
Simply using AI, which one writes "it said
[Redacted by the Mentors -- AI is not a valid reference at PF]" isn't valid since there is not attribution to the source(s) from which the AI took information. Please provide the original source of the data.
The values of 10^-3 to 10^-1 cm^-3 appear to be incorrect.
From the ArXiV paper cited, in the Introduction one finds the statement with respect to Cygnus-X
The 7° × 7° area harbors several Wolf-Rayet stars and hundreds
of O-type stars grouped in powerful OB associations. It also
contains vast HI and molecular gas complexes with masses ex-
ceeding 106 M⊙. The presence of potential particle accelerators,
namely massive stars and supernova remnants, and targets for
γ-ray production (dense gas regions) make several parts of this
region effective γ-ray emitters.
Note the dense gas statement.
One has to consider what part of the Cygnus-X star-forming regions is producing the PeV γ-rays.
In the paper, Filamentary structures of ionized gas in Cygnus X, one finds the statement in the Abstract:
The electron densities of the filamentary structure range between 10 ≲ ne [cm−3] ≲ 400 with a median value of 35 cm−3,
https://www.aanda.org/articles/aa/full_html/2022/08/aa42596-21/aa42596-21.html
in the Abstract, one finds a subsequent statement:
More than half of the filamentary structures are likely photoevaporating surfaces flowing into a surrounding diffuse (~5 cm−3) medium.
In the second and third paragraphs of the Introduction, one finds various values for densities in various regions
As a result of peculiar motion and/or inhomogeneities in the medium, the star, its photons, and the gas it ionizes enter a surrounding low-density medium (
ne ~ 0.1–100 cm
−3) within a few megayears (e.g.,
Mezger 1978).
Within the plane of the Galaxy, photoionized gas is found in a variety of environments (and referred to with a variety of different names). Dense (ne > 103 cm[/sup]−3[/sup]) ionized gas pervades H II regions of a few parsecs in size.
From leaky H II regions, ionizing photons escaping through porous material create (partially) ionized gas (1–100 cm[/sup]−3[/sup]) in the envelopes of H II regions. This diffuse ionized gas (1–100 cm[/sup]−3[/sup]) permeates to larger volumes in blister H II regions. Assisted by SN explosions, massive stars create large excavated regions or plasma tunnels that contain fully ionized gas (1–10 cm[/sup]−3[/sup]).
In the fourth paragraph in the Introduction:
Mezger (1978) estimated that 84% of ionizing photons are emitted by O stars outside of compact H II regions, in gas characterized by densities of
ne ≈ 5–10 cm[/sup]−3[/sup]
dubbed extended low-density (ELD) H II gas.
Note the aforementioned densities are much greater than the values (10^-3 to 10^-1 cm^-3) stated in the original post.
The ArXiV paper refers to HI regions vs HII regions. See the significance here
http://csep10.phys.utk.edu/OJTA2dev/ojta/c2c/milkyway/interstellar/regions_tl.html
https://en.wikipedia.org/wiki/H_I_region ,
https://en.wikipedia.org/wiki/H_II_region
In the following paper, Chandra X-ray spectroscopy of focused wind in the Cygnus X-1 system
https://www.aanda.org/articles/aa/full_html/2016/06/aa22490-13/aa22490-13.html
Large density and temperature inhomogeneities are present in the wind, with a fraction of the wind consisting of clumps of matter with higher density and lower temperature embedded in a photoionized gas.
One has to identify the local conditions of the source of PeV or even TeV photons.
Local pressure will be determine the product of particle (atomic, ion, electron) density (n) and temperature (T) by P = nkT, where k is the Boltzmann constant.
