Problems For Self-Interacting Dark Matter

In MOND, due to the external field effect, you expect a bimodal distribution. In CDM is should be a more continuous distribution. SIDM should have a single value.

Self-interacting dark matter (SIDM) has been proposed to address small-scale challenges faced by the cold dark matter (CDM) paradigm, such as the diverse density profiles observed in dwarf galaxies. In this study, we analyze the kinematics of dwarf galaxies by incorporating the effects of gravothermal core collapse into SIDM models using a semi-analytical subhalo framework. Our analysis covers the stellar kinematics of both classical and ultrafaint dwarf galaxies. The results indicate a bimodal preference for small and large self-interaction cross sections in ultrafaint dwarf galaxies, while in classical dwarfs, larger cross sections progressively decrease the model's statistical support. The combined analysis decisively prefers CDM to SIDM when the self-interaction cross section per unit mass, σ/m, exceeds ∼0.2 cm2/g, if a velocity-independent cross section is assumed. Our study significantly enhances our understanding of dark matter dynamics on small scales.

Shin'ichiro Ando, et al., "Stringent Constraints on Self-Interacting Dark Matter Using Milky-Way Satellite Galaxies Kinematics" arXiv:2503.13650 (March 17, 2025).

Celtic Origins Traced With Ancient DNA

The Urnfield culture probably was a major factor spreading Celtic languages, and the Celtic languages and culture probably originated not with the Hallstatt Culture but with an early demic diffusion of an earlier culture found in Romania around 2,000 BCE to 1,200 BCE. The body text of the introduction explains that:

The debate is currently focused around three main models: (1) a Late Neolithic/Early Bronze Age spread along the Atlantic seaboard linked to the Bell Beaker Culture; (2) a Bronze Age spread from France, Iberia or Northern Italy; and (3) a Late Bronze Age/Early Iron Age spread from Central Europe associated with the Hallstatt and La Tène Cultures. Thus, the appearance and dispersal of the Celtic language constitutes a key question concerning the cultural formation of Bronze and Iron Age Europe.

In an accompanying paper, we report the generation of 752 new genomes, including 126 originating from France, Germany, Austria, and the British Isles, which are of immediate relevance to these questions.

Figure 2 in the paper looks at relative contributions of ancestry across Europe around 2300 BCE and 500 BCE.

Celtic languages, including Irish, Scottish Gaelic, Welsh and Breton, are today restricted to the Northern European Atlantic seaboard. However, between 3 and 2 thousand years before present (BP) Celtic was widely spoken across most of Europe. 

While often associated with Bell Beaker-related populations, the spread of this prominent Indo-European linguistic cluster remains debated. Previous genomic investigations have focused on its arrival to specific regions: Britain, Iberia and Southwestern Germany. 

Here, we utilize new genomic data from Bronze and Iron Age Europe to investigate the population history of historically Celtic-speaking regions, and test different linguistic theories on the origins and early spread of the Celtic languages. We identify a widespread demographic impact of the Central European Urnfield Culture. We find ancestry associated with its Knovíz subgroup in the Carpathian Basin to have formed between 4 – 3.2 kyr BP, and subsequently expanded across much of Western Europe between 3.2 and 2.8 kyr BP. This ancestry further persisted into the Hallstatt Culture of France, Germany and Austria, impacting Britain by 2.8 kyr BP and Iberia by 2.5 kyr BP. 

These findings support models of an Eastern Central rather than a Western European center of spread for a major component of all the attested Celtic languages. Our study demonstrates, yet again, the power of ancient population genomics in addressing long-standing debates in historical linguistics.

Hugh McColl, et al., "Tracing the Spread of Celtic Languages using Ancient Genomics" bioRxiv (March 1, 2025). More commentary and analysis at Bernard's blog.

Humans In African Jungles 150,000 Years Ago

Modern humans existed in wet tropical forests of West Africa about 150,000 years ago, contrary to the believe that humans could only survive in this kind of ecological environment through trade with farmers.

Humans emerged across Africa shortly before 300 thousand years ago (ka). Although this pan-African evolutionary process implicates diverse environments in the human story, the role of tropical forests remains poorly understood. 

Here we report a clear association between late Middle Pleistocene material culture and a wet tropical forest in southern Côte d’Ivoire, a region of present-day rainforest. Twinned optically stimulated luminescence and electron spin resonance dating methods constrain the onset of human occupations at Bété I to around 150 ka, linking them with Homo sapiens. Plant wax biomarker, stable isotope, phytolith and pollen analyses of associated sediments all point to a wet forest environment. 

The results represent the oldest yet known clear association between humans and this habitat type. The secure attribution of stone tool assemblages with the wet forest environment demonstrates that Africa’s forests were not a major ecological barrier for H. sapiens as early as around 150 ka.

Eslem Ben Arous, et al.,"Humans in Africa’s wet tropical forests 150 thousand years ago" Nature (February 26, 2025).

Galaxy Rotation Direction Is Not Random

I note this fact without exploring the most speculative explanations for this still unsolved problem in astrophysics and cosmology.

The $10 billion telescope, which began observing the cosmos in the Summer of 2022, has found that the vast majority of deep space and, thus the early galaxies it has so far observed, are rotating in the same direction. While around two-thirds of galaxies spin clockwise, the other third rotates counter-clockwise.

In a random universe, scientists would expect to find 50% of galaxies rotating one way, while the other 50% rotate the other way. This new research suggests there is a preferred direction for galactic rotation.

From here citing this paper whose abstract is also provided:

JWST provides a view of the Universe never seen before, and specifically fine details of galaxies in deep space. JWST Advanced Deep Extragalactic Survey (JADES) is a deep field survey, providing unprecedentedly detailed view of galaxies in the early Universe. The field is also in relatively close proximity to the Galactic pole. Analysis of spiral galaxies by their direction of rotation in JADES shows that the number of galaxies in that field that rotate in the opposite direction relative to the Milky Way galaxy is ∼50 per cent higher than the number of galaxies that rotate in the same direction relative to the Milky Way. The analysis is done using a computer-aided quantitative method, but the difference is so extreme that it can be noticed and inspected even by the unaided human eye. These observations are in excellent agreement with deep fields taken at around the same footprint by Hubble Space Telescope and JWST. 

The reason for the difference may be related to the structure of the early Universe, but it can also be related to the physics of galaxy rotation and the internal structure of galaxies. In that case the observation can provide possible explanations to other puzzling anomalies such as the H(o) tension and the observation of massive mature galaxies at very high redshifts.

Lior Shamir, "The distribution of galaxy rotation in JWST Advanced Deep Extragalactic Survey" 538(1) Monthly Notices of the Royal Astronomical Society 76–91 (February 17, 2025). https://doi.org/10.1093/mnras/staf292