Dark matter atoms may form shadowy galaxies with rapid star formation

Glad to see this type of thinking being considered and tested. Considering the diversity of the 20% of matter that we can see, it seems very naive to expect that the 80% that we cannot see, but infer (from gravitational effects), would be only one simple thing (particle type or whatever).

On the other hand, if we can simply assume that there is the same complexity, or maybe 4 times the complexity that we see in visible matter, then we can use all of that as "fitting parameters" for making the Big Bang Theory match whatever observations we make in the future that otherwise would seem to undercut its credibility.

It is not just important, it is necessary to constantly keep in mind what is an observation and what is an assumption when doing this sort of thinking. Otherwise, people begin to think that they have "proven" their thinking is correct simply because they have managed to not violate the observations with what might be a wholly unrealistic set of assumptions that are only internally consistent, not really proven. (That is where I am concerned that the BBT has already gone - requiring that 95% of its mass and energy are based on assumptions, rather than detected materials or forces that obey known physical mechanisms.)

In the case of the BBT, I don't think that there is even a completely consistent set of assumptions. So, thinking that is broad enough to question some of those assumptions is something that I welcome, especially if it looks at some of the potentials for inconsistencies.
Well, this is an interesting report on DM. The reference paper cited is 23-page PDF. I note from the paper:

Draft version April 21, 2023
Typeset using LATEX twocolumn style in AASTeX631
Simulating Atomic Dark Matter in Milky Way Analogues, https://arxiv.org/abs/2304.09878

"ABSTRACT Dark sector theories naturally lead to multi-component scenarios for dark matter where a subcomponent can dissipate energy through self-interactions, allowing it to eciently cool inside galaxies.
We present the rst cosmological hydrodynamical simulations of Milky Way analogues where the
majority of dark matter is collisionless Cold Dark Matter (CDM), but a sub-component (6%) is strongly
dissipative minimal Atomic Dark Matter (ADM)."

"1. INTRODUCTION...Dark sectors frequently include a fraction of DM with dissipative self-interactions, which can cool and clump in opposition to the purely gravitational dynamics of CDM. A useful benchmark model for such scenarios is Atomic Dark Matter (ADM), which consists of a dark proton, p0, and dark electron, e0, that interact through a massless dark photon with coupling, 0 (Kaplan et al. 2009). The ADM can form a dark hydrogen bound-state and radiatively cools in direct analogy to the Standard Model. We assume a minimal model that has no dark nuclear physics and only couples to the Standard Model through gravity. Moreover, we assume that the ADM abundance is set asymmetrically, so that the abundance of dark anti-particles is negligible (Zurek 2013; Kaplan et al. 2011)."

I found 7 references to assume or assumed in the paper. Also some other good stuff :)

"On cosmic scales, ADM manifests through dark acoustic oscillations and contributions to Ne (Cyr-Racine
et al. 2014; Gurian et al. 2022a). Current cosmological constraints allow for ADM to comprise & O(10%) of
the DM for a wide range of parameters (Bansal et al. 2022b,a). On much smaller scales, the signatures of
an ADM sub-component can potentially be spectacular. ADM gas clouds can collapse and condense into dark compact objects, giving rise to dark white dwarfs (Ryan & Radice 2022) and non-stellar-mass black holes (Shandera et al. 2018; Fernandez et al. 2022), as well as mirror (neutron) stars (Curtin & Setford 2020a,b; Hippert et al. 2022b,a) (if there is dark nuclear physics)."

It is time to show a database listing all DM stuff now :)
Dark atoms? Is that with dark protons, dark neutrons, dark electrons, dark quarks? Emitting dark photons and dark neutrinos? And dark antimatter? Interesting indeed!
I have a tendency to forget the dark part, and this article makes me want to forget it even more since we detect it via its gravitational effect, which is a universal effect, a uniform [everywhere-at-once] effect . . . regardless of degree.

Light follows spacetime curvature. There may be more paths to the universe than just a light following 1-dimensional curvature and gravity may deal in one or more of those other paths (one or more other dimensions of pathing). Thus, the only reason for the darkness may be that we just don't observe that fold, or level, or whatever, in spacetime from our position, or velocity, or horizon. If we were travelers in and through the universe, we might observe and reach far more of the universe -- finding a far different, possibly far larger, far wider and deeper, universe (thus possibly many more universes belonging to our own local all-in-one multiverse universe) -- than we can possibly observe from Earth . . . or any one place in it (again, once more, "the map (the light map arrived to Earth) is not the territory").
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