Astrophysics papers — 2026-10-04

The Morning Preprint — this day as one edition: the day's papers, the five things worth knowing, and the episodes behind them.

Today's focus is on understanding how dense matter behaves under extreme conditions. This is crucial because binary neutron star mergers offer a unique laboratory to study physics that cannot be replicated on Earth. We are looking at the dense-matter equation of state in these events, which dictates everything from the inspiral and merger dynamics to the structure of the resulting remnant and how heavy elements are forged through r-process nucleosynthesis.

The connection between microscopic physics and observable signatures is key here. This involves linking tidal deformability to post-merger gravitational-wave spectra, kilonova light curves, short gamma-ray bursts, and afterglows. This connects directly to the work by AKMPC. Furthermore, observations of events like GW170817 help constrain this dense matter physics when combined with neutron star mass and radius measurements from laboratory experiments and theoretical many-body calculations.

Beyond compact objects, we are also examining how gravitational laws are constrained by wide binary stars using Gaia DR3 data. This work tests Milgromian dynamics against Newtonian predictions for orbits at large separations. It finds a strong preference for Newtonian gravity in most analyses, although it suggests MOND might need modification on small scales.

This contrasts with the work on cosmological structure where semi-analytical approaches use Jeans Filtering Functions to describe how baryonic pressure shifts the filtering scale in second-order perturbation theory. The most significant finding relates to how coupling eROSITA with wide-field time-domain photometric and multi-wavelength surveys offers a highly efficient strategy for uncovering the hidden population of compact object binaries.

This approach yielded two distinct source samples. One sample consisted of 151 periodically variable sources from which a refined subset of 43 high-priority compact object binary candidates was identified. The second sample contained 1958 distance-constrained sources selected based on elevated X-ray luminosities or high flux ratios. Cross-matching these samples with radio catalogs revealed seven radio-emitting sources, pointing to four promising XRB candidates.

This efficiency is complemented by work investigating the evolution of a synchronous planet-moon pair due to solar tides. This addresses the demise of a synchronous moon that initiated Mars' triaxiality. This study suggests that while stellar tides cause the orbit of a planet-moon pair to shrink, their synchronism can be transiently stable until a critical distance is reached where the moon desynchronizes and spirals down.

The authors applied this mechanism to Mars and Nerio, finding that the planet's spin rate at the moment of desynchronization matches its current rate to one decimal place. The implications for Mars are complex. Post-desynchronization evolution involved continued spin-up during Nerio's descent followed by subsequent despinning due to solar tides.

The work also notes that Nerio likely perished during the LHB hazard period, though this verdict remains subject to change pending new data on Mars' oceans. This demise is indirectly supported by the presence of tidalites in sediments in Vastitas Borealis and Gale Crater, which occurred while Nerio was descending through the ocean.

Today's papers

The papers

Important terms

Dense-matter equation of state
This describes how matter behaves under extreme conditions, which is vital for understanding binary neutron star mergers and how heavy elements are created during r-process nucleosynthesis.
Tidal deformability
This property of compact objects is linked to observable signatures like gravitational waves and kilonova light curves, helping us connect microscopic physics to astronomical observations.
MOND (Modified Newtonian Dynamics)
This is a theory that suggests gravity might behave differently than Newton's law at very small scales, tested here by observing wide binary stars using Gaia data.
Jeans Filtering Functions
These functions are used in second-order perturbation theory to describe how the pressure from baryonic matter affects the filtering scale in cosmological structure studies.