New observations of the ultra-diffuse galaxy NGC1052-DF2, published in Nature by van Dokkum et al., seem to show that it contains an unusually low amount of dark matter, perhaps barely any at all. This conclusion was reached after independently computing the luminous and gravitational mass of the galaxy, which, contrary to all other galaxies observed up to date, seem to match. This means that there is little room for the presence of non-luminous (or “dark”) matter in NGC1052-DF2. This striking observation may pose a challenge to popular dark matter paradigms and raises the question of what astrophysical processes could have lead to its formation.
There are more than one hundred billion galaxies in the observable Universe. Given this enormous number and the fast rate at which they are discovered and catalogued nowadays, one would think that a new observation probably wouldn't have much scientific relevance. But sometimes we encounter an exciting surprise, as is the case of NGC1052-DF2 (DF2 for short), a galaxy studied by van Dokkum et al. in their recent Nature paper [1].
The observed antineutrino flux from nuclear reactors is consistently lower than predicted. This anomaly could hint at oscillations of active neutrinos into a new sterile neutrino species, or it could simply be a reflection of underestimated systematic uncertainties in the theoretical flux prediction. We review the status of both hypothesis in view of recent developments. In particular, we scrutinize recent Daya Bay results, which aim to determine whether the deficit depends on the isotope from which neutrinos are produced (as would be likely if the problem is with the flux prediction), or is independent thereof (as would be expected if the sterile neutrino hypothesis is true). We also comment on new short-baseline data, and we discuss reactor data in the context of a global fit.
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