Monotonicity of the cores of massive stars

TL;DR

This study demonstrates that the internal structures and evolutionary properties of massive stars follow a monotonic pattern, providing a simple empirical principle to characterize their cores despite complex underlying physics.

Contribution

The paper reveals that the cores of massive stars exhibit monotonic relationships across various properties, offering a new empirical rule for understanding stellar evolution.

Findings

Core properties like density, entropy, and chemical distribution are monotonic.

Lifetimes and explosion characteristics follow a monotonic sequence.

Monotonicity serves as an empirical principle for massive star cores.

Abstract

Massive stars are linked with diverse astronomical processes and objects including star formation, supernovae and their remnants, cosmic rays, interstellar media, and galaxy evolution. Understanding their properties is of primary importance for modern astronomy, and finding simple rules that characterize them is especially useful. However, theoretical simulations have not yet realized such relations, instead finding that the late evolutionary phases are significantly affected by a complicated interplay between nuclear reactions, chemical mixing, and neutrino radiation, leading to non-monotonic initial mass dependencies of the iron core mass and the compactness parameter. We conduct a set of stellar evolution simulations, in which evolutions of He star models are followed until their central densities uniformly reach 10$^{10}$ g cm$^{-3}$, and analyze their final structures as well as their evolutionary properties including the lifetime, surface radius change, and presumable fates after core collapse. Based on the homogeneous data set, we have found that monotonicity is inherent in the cores of massive stars. We show that not only the density, entropy, and chemical distributions, but also their lifetimes and explosion properties such as the proto-neutron-star mass and the explosion energy can be simultaneously ordered into a monotonic sequence. This monotonicity can be regarded as an empirical principle that characterizes the cores of massive stars.