Strong Field General Relativity Fits The Data

All strong gravitational field observations are indistinguishable from general relativity. 

The troublesome cases are in weak gravitational fields in very large systems like galaxies that are usually modeled with simple Newtonian gravity because the math necessary to calculate their behavior in full GR is too hard and is assumed by good arguments, but without actual calculations that could capture non-perturbative effects, to be insignificant.

The signals from the LIGO-Virgo-KAGRA network of gravitational-wave (GW) detectors allow us to perform sensitive tests of general relativity (GR) in the dynamical and strong-field regime of gravity. 

We present the results of seven tests of GR using the observed binary signals in the fifth GW Transient Catalog (GWTC-5.0), i.e., up to and including the second part of the fourth observing run (O4b). We restrict our analysis to the confident signals, henceforth called events, observed by at least two detectors that have estimated false alarm rates ≤ 10^−3 yr^−1. These include 72 events from O4b and five events from the first part of the fourth observing run that are now analyzed due to their increased significance from updated search results, bringing the total number of events for tests of GR in the cumulative GWTC to 168. 

After subtracting the best-fit waveforms, we find the residuals are consistent with detector noise for all events considered. We also find no strong evidence for additional polarizations beyond those predicted by GR. 

We perform tests of GW generation, improving the constraints on deviations from the GR post-Newtonian coefficients by factors of 1.2-2.6. 

Finally, we find overall consistency of the remnants with GR using both time- and frequency-domain methods. For GW240621_195059, postmerger data are consistent with the dominant quadrupolar (ℓ = |m| = 2) mode of a Kerr black hole and its first overtone, with spurious high-frequency content preventing a spectroscopic constraint of GR. In the frequency-domain ringdown analysis, the GR prediction lies in the tails of the combined results, possibly due to the limited catalog size. 

However, the combined results indicate improved consistency with GR over GWTC-4.0, owing to the contribution of GW250114 with a network matched-filter signal-to-noise ratio of 76.9. Overall, we find no evidence for physics beyond GR.

The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration, "GWTC-5.0: Tests of General Relativity" arXiv:2607.19293 (report number LIGO-P2500781) (July 21, 2026).

Neutrinos Are Very Likely Very Light

Adopting the cosmological bounds on the sum of the neutrino masses and making some other unambitious assumptions, this paper argues that the lightest of the three neutrino masses is less than 2.3 meV and considers a possible phenomenological relations between the three neutrino masses. Direct measurements of the electron neutrino mass at the Katrin experiment bound it at less than 450 meV with good prospects of reducing the bound to 200 meV, but that is still at least two orders of magnitude less than the likely true value.

By way of comparison, the mass of an electron is about 511,000,000 meV, and the first generation quarks are in the low single digit billions of meVs. 

Determining the absolute neutrino mass scale remains one of the most compelling challenges in particle physics. To constrain theoretical models, establishing precise relations among neutrino masses is essential. We propose a simple integral representation of the neutrino mass-squared differences Δm(ij)^2 that provides a complementary perspective on these oscillation parameters. We then demonstrate its utility through several examples. 

Specifically, assuming stringent cosmological bounds that confine the sum of neutrino masses near the normal ordering floor, we derive an analytical condition for the lightest neutrino mass, m(1) < √(61Δm(21)^2)/30. Using recent data from the JUNO experiment, this yields a competitive upper limit of m(1) < 0.0023 eV (95% C.L.). 

We also formulate practical analytical bounds for m(2) and m(3) adaptable to future data, and translate the results into allowed ranges for the effective electron and Majorana neutrino masses m(νe) and m (ββ). Finally, we show that neutrino mass relations of the Gatto-Sartori-Tonin type emerge directly from the proposed integral representation.

I. Alikhanov, "Integral representation of the neutrino mass-squared differences" arXiv:2607.19340 (July 21, 2026).

Medieval DNA From Russia

Medieval ancient DNA from Eastern Europe is consistent with the historical and linguistic narrative of the peoples who make up the Russian state.

The foundation of the first ancient Rus’ state occurred as a result of the consolidation of diverse communities inhabiting Eastern Europe during the second half of the first millennium CE. Historical sources imply that these communities mostly include East Slavs, whose settlement across a vast territory led to the emergence of the East Slavic/Rus’ culture within the Rus’ state. 

We generated genomic data for 200 medieval individuals from different locations to elucidate the origin and genetic structure of the Rus’ population during the early stages of the state formation. Our findings reveal a genetic continuum predominantly shaped by two key genetic groups: a broad Slavic-related continuity of different genetic subclusters of Rus’ occupying the enormous European Plain area, and a Fenno-Ugrian (Uralic)-related component in the Northern Rus’ region. Importantly, both groups have a shared genetic substrate inherited from preceding ancient Baltic region populations. 

To scale Scandinavian ("Viking") heritage, we traced minor Scandinavian genetic lineages that did not make up the dominating genetic stratum of the early Rus’ state. 

Our study presents the first comprehensive genomic image of the medieval Rus’, highlighting the intricate cultural and genetic interactions between Slavic, Fenno-Ugrian, and other groups that formed the first Rus’ state affecting Europe’s history.

Andreeva et al., Genetic history of Rus’, bioRxiv (December 30, 2025), doi: https://doi.org/10.64898/2025.12.30.695215 (Hat tip to Davidski at Eurogenes).

The Widest Galaxy

The galaxy with the greatest diameter ever observed (IC1101) has a diameter of 520 kiloparsecs (1.7 million light years), and it is still growing. By comparison, our Milky Way galaxy has a diameter of about 100,000 light years (about 31 kiloparsecs).