LambdaCDM Still Broken

The dark galaxy "Nube", the largest low surface brightness galaxy of its kind, shouldn't happen in the LambdaCDM model:

With a stellar mass of ∼4 × 10⁸ M_⊙ and a half-mass radius of R_e = 6.9 kpc (corresponding to an effective surface density of ⟨Σ⟩_e ∼ 0.9 M_⊙ pc⁻²), Nube is the most massive and extended object of its kind discovered so far. The galaxy is ten times fainter and has an effective radius three times larger than typical ultradiffuse galaxies with similar stellar masses. Galaxies with comparable effective surface brightness within the Local Group have very low mass (tens of 10⁵ M_⊙) and compact structures (effective radius R_e < 1 kpc). Current cosmological simulations within the cold dark matter scenario, including baryonic feedback, do not reproduce the structural properties of Nube.

In educated layman's terms:

Nube is an almost invisible dwarf galaxy discovered by an international research team led by the Instituto de Astrofísica de Canarias (IAC) in collaboration with the University of La Laguna (ULL) and other institutions.

The name was suggested by the 5-year-old daughter of one of the researchers in the group and is due to the diffuse appearance of the object. Its surface brightness is so faint that it had passed unnoticed in the various previous surveys of this part of the sky due to the object's diffuse appearance as if it were some kind of ghost. This is because its stars are so spread out in such a large volume that "Nube" (Spanish for "Cloud") was almost undetectable.

This newly discovered galaxy has a set of specific properties which distinguish it from previously known objects. The research team estimate that Nube is a dwarf galaxy 10 times fainter than others of its type, but also 10 times more extended than other objects with a comparable number of stars. . . . this galaxy is one-third of the size of the Milky Way[.]

The authors, in the introduction, working from the dark matter particle paradigm, recounts some of the LambdaCDM model's problems:

Many cosmological observations at large scales suggest that dark matter can be well described as a cold and collisionless fluid (see e.g. White & Rees 1978; Blumenthal et al. 1984; Davis et al. 1985; Smoot et al. 1992). 

Nonetheless, the predictions of this model at galactic scales have faced an increasing number of challenges, such as the “cusp-core” problem, the “missing satellite” problem, and the “too-big-to-fail” problem (see e.g. Boylan-Kolchin et al. 2011; Weinberg et al. 2015; Del Popolo & Le Delliou 2017). 

Many of these problems can be mitigated by the effect of baryon feedback on the dark matter distribution (see e.g. Davis et al. 1992; Governato et al. 2010; Di Cintio et al. 2014). However, if the number of stars or their spatial density were low enough, it would be difficult to argue that stellar feedback could be responsible for affecting the dark matter distribution, because there would not be enough energy to change the location of the dark matter (see e.g. Peñarrubia et al. 2012; Oñorbe et al. 2015). 

In parallel, while the direct detection of dark matter particles remains out of reach, other alternatives to the cold dark matter model have gained traction, and are being applied to solve the small-scale challenges. These include the warm dark matter scenario (see e.g. Sommer-Larsen & Dolgov 2001; Bode et al. 2001), self-interacting dark matter (Spergel & Steinhardt 2000), and fuzzy dark matter (composed of ultralight axions with masses in the 10^ −23 – 10^−21 eV range; see e.g. Sin 1994; Hu et al. 2000; Matos & Arturo Ureña-López 2001). 

For these reasons, the search for objects with extremely low stellar surface densities (where the effect of baryonic feedback is not expected to be relevant) promises to probe the microphysical nature of dark matter, that is, the properties of the dark matter particle.

I don't think that the dark matter particle paradigm is correct. Dark matter and dark energy phenomena are probably gravitational law phenomena that arise from our misunderstanding of how gravity works in galaxy scale and galaxy cluster scale systems. But, ruling out various dark matter particle scenarios does advance the cause of demonstrating that the LambdaCDM Standard Model of Cosmology is wrong, and narrows the task of showing that the cause of these phenomena is gravitational rather than particle based.

It is frustrating that any professional astronomers still take the LambdaCDM model seriously, but paradigm changes like this take hold when the proponents of the old model die, not when new evidence rules them out, scientific method be damned.