Guoliang Lü

The stability of binary mass transfer is a critical problem for binary evolution. We systematically calculate the adiabatic mass-loss model for naked helium stars with masses ranging from 10 M _⊙ to 80 M _⊙ to study the critical mass ratio ( q _crit ) of Wolf–Rayet binaries. We set up two prescriptions about Wolf–Rayet stellar wind and consider the isotropic reemission effect during adiabatic mass loss. Results of the critical mass ratio for conserved dynamically unstable mass transfer show that most of the no-wind helium stars in the main sequence (HeMS) have 0.7 < q _crit < 3.0 and helium stars on the Hertzsprung gap (HeHG) have 1.5 < q _crit < 27. With the Wolf–Rayet star wind effect, the q _crit gets lower on a certain evolutionary stage. With the isotropic reemission effect, the q _crit gets larger for early evolutionary stage helium stars and lower for late-evolutionary stage helium stars. Based on fully nonconserved mass transfer, the criteria for HeMS stars are 1.0 < q _crit < 2.8 and HeHG stars are 1.5 < q _crit < 5.0. Compared with the widely used criterion q _crit = 3 (HeMS) and q _crit = 4 (HeHG), our result becomes more unstable for the HeMS stars and more stable for the HeHG stars. Our work could be applied to the binary mass-transfer stage of massive helium binaries, such as Wolf–Rayet star binaries and high-mass X-ray binaries with Wolf–Rayet star companions. It can be applied to the binary population synthesis studies for the formation of special objects, such as double black hole mergers.

Thermonuclear (Type I) X-ray bursts from accreting neutron stars (NSs) offer a means to determine NS mass ( M ) and radius ( R ) and thereby probe the properties of matter at supranuclear density. A subset of these events, photospheric radius-expansion bursts, provide a particularly powerful tool to constrain the NS M and R . Here, we apply the direct cooling-tail method to 2S 0918−549, using a rare superexpansion burst observed by Rossi X-ray Timing Explorer. We fit only the posttouchdown data within F / F _td ∈ [0.6, 0.95], employing modern atmosphere models (pure-He and metal-enriched). The pure-He atmosphere yields a good description of the cooling tail ( χ ² / ν = 18.12/14), whereas metal-rich models fail; information-criterion tests (Akaike information criterion/Bayesian information criterion) disfavor adding a free absorption edge in every time bin, indicating that heavy-element ashes are unnecessary. The joint fit gives a distance d = 4.1–5.3 kpc and mass–radius constraints M = 1–2 M _⊙ and R = 9.7–11.9 km (99% confidence). These results suggest that representative families of both gravity-bound and self-bound equations of state remain viable at the 1 σ confidence level.

We introduce a novel parameterization of supernova neutrino energy spectra with a clear physical motivation. Its central parameter, τ ( t ), quantifies the characteristic thermal-diffusion area during the explosion. When applied to the historic SN 1987A data, this parameterization yields statistically significant fits and provides robust constraints on the unobserved low-energy portion of the spectrum. Beyond this specific application, we demonstrate the model’s power on a suite of 3D core-collapse supernova simulations, finding that the temporal evolution of τ ( t ) distinctly separates successful from failed explosions. Furthermore, we constrain the progenitor mass of SN 1987A to approximately 19 solar masses by applying a smoothed isotonic regression, while noting the sensitivity of this estimate to observational uncertainties. Moreover, in these simulations, τ ( t ) and the gravitational-wave strain amplitude display a strong, synergistic coevolution, directly linking the engine’s energetic evolution to its geometric asymmetry. This implies that the thermodynamic state of the explosion is not only imprinted on the escaping neutrino flux but also recorded in the shape of the energy spectrum. Our framework therefore offers a valuable tool for decoding the detailed core dynamics and multimessenger processes of future Galactic supernovae.

Dark matter heating in planets has been proposed as a potential probe for dark matter detection. Assuming near-equilibrium conditions, we find that the energy input from dark matter raises planetary temperatures and accelerates rotation. The distribution of energy between heating and rotational acceleration depends on both planetary properties and external inputs, suggesting that previous studies may have overestimated the heating contribution. At high dark matter densities, planetary rotation stabilizes earlier and becomes primarily governed by dark matter effects.

In axion models, interactions between axions and electromagnetic waves induce frequency-dependent time delays determined by the axion mass and decay constant. These small delays are difficult to detect, limiting the effectiveness of traditional methods. We compute such delays under realistic radio telescope conditions and identify a prominent dispersive feature near half the axion mass, which appears nondivergent within the limits of observational resolution. Based on this, we develop a machine learning method that achieves 90% classification accuracy and demonstrates performance well in low signal-to-noise regimes. The method’s robustness is confirmed against false positives using both simulated noisy data and real-world, known-null observations. Future improvements in optical clock precision and telescope bandwidth, particularly with instruments such as the Qitai Radio Telescope, may enhance constraints on the axion decay constant by up to 4 orders of magnitude in the 10 ⁻⁶ ∼ 10 ⁻⁴ eV mass range.