Exploring how dark matter alters electron-capture supernovae and the birth of neutron stars

Electron-capture supernovae (ECSNe) are stellar explosions that occur in stars with initial masses around 8–10 times that of the sun. These stars develop oxygen-neon-magnesium cores, which become unstable when electrons are captured by neon and magnesium nuclei.

The resulting loss of electron pressure triggers core collapse, leading to a supernova explosion and the formation of a neutron star—an extremely dense star composed mostly of neutrons.

Researchers at INFN-Pisa and the University of Pisa recently carried out a study aimed at shedding new light on how a hypothetical type of dark matter, called asymmetric dark matter (ADM), could influence the collapse of the ECSN progenitor cores and the subsequent formation of neutron stars.

Their paper, published in the Journal of High Energy Astrophysics, presents the first self-consistent stellar-structure model of the possible contribution of ADM to this astrophysical process.

“My inspiration to carry out the research reported in our recent article published in JHEAP came a little over a year ago, when I came across an interesting study by Hiramatsu et al. published in 2021,” Ignazio Bombaci, co-author of the paper, told Phys.org.

“In their work, the authors showed that supernova 2018zd (SN2018zd) represented the first convincing observational evidence of an ECSN, a new type of stellar explosion proposed in the early 1980s by Japanese astrophysicist Ken’ichi Nomoto and his collaborators.”

Before Bombaci stumbled on the 2021 paper by Hiramatsu and his colleagues, he was supervising the work of Domenico Scordino, who was completing his Master’s degree in Physics at the University of Pisa. Together with his student, he had been investigating the possible effects of fermionic ADM on the structural properties of neutron stars.

“After reading the paper, it immediately became clear to me that the presence of fermionic dark matter in the degenerate core of oxygen, neon, and magnesium (¹⁶O, ²⁰Ne, ²⁴Mg) of the ECSN progenitor star could strongly influence the ECSN process, particularly regarding the critical mass value of the degenerate stellar core beyond which electron capture on ²⁰Ne and ²⁴Mg nuclei can occur,” said Bombaci.

“Most importantly, I saw the possibility of forming neutron stars with masses well below one solar mass—that is, below the smallest mass measured so far (M = 1.174 solar masses) for the neutron star associated with the pulsar PSR J0453+1559.”

The primary objective of the researchers’ study was to explore the impact of dark matter on the collapse of the ECSN progenitor core, the subsequent explosion, and the birth of the neutron star. In their analyses, they treated ordinary matter and dark matter as two interpenetrating fluids that interact solely via gravitational effects.

“To do this, we used a general relativistic two-fluid formalism, which extends the standard compact star structure equations to describe equilibrium configurations where two fluid components coexist under a shared gravitational field,” explained Scordino, co-author of the paper.

“For ordinary matter, we modeled neon‑rich white dwarfs (the typical progenitors of electron‑capture supernovae) using equations of state (EOS) that include the physics of electron capture. For the dark matter, we assumed it behaves like a cold, ideal, degenerate Fermi gas, while, to model the ordinary matter inside the neutron star, we use a microscopic EOS using a quantum many-body approach.”

Bombaci, Scordino, and their colleague Vishal Parmar subsequently solved stellar structural equations numerically, looking at different dark matter particle masses and fractions. This allowed them to make predictions about how the presence of dark matter would change the density profile of the white-dwarf-like core of the ECSN progenitor and influence the threshold mass at which its collapse would occur.

“This approach allowed us to map progenitor white dwarfs directly to their neutron star remnants and to quantify how dark matter could lower the explosion energy and produce unusually low‑mass neutron stars,” said Scordino.

“Ultimately, we showed that dark matter can make white-dwarf-like cores collapse at a lower gravitational mass, leading to weaker explosions and producing unusually low‑mass neutron stars.”

This recent study introduces the first stellar structure-informed model that outlines the role of ADM in the collapse of white dwarfs, the ECSNe energetics and the subsequent emergence of neutron stars. This model could inform both astrophysical studies focusing on the ECSNe process and potentially future dark matter searches.

“By treating ordinary matter and dark matter as two fluids interacting through gravity only, we showed that even a modest amount of dark matter can compress white‑dwarf cores enough to trigger collapse at lower masses than previously thought,” said Parmar, co-author of the paper.

“This opens up a new pathway for forming unusually light neutron stars, well below the standard mass range predicted by conventional models.”

Overall, the team’s model suggests that very low‑energy supernovae or unexpectedly light neutron stars could be indirect signatures of dark matter at work inside stars. Follow-up studies could further explore this possibility and its possible implications for dark matter searches.

“More broadly, our study highlights that stellar explosions, traditionally studied only in terms of nuclear and particle physics, may also serve as natural laboratories for probing the properties of dark matter, giving us a new astrophysical window into one of the biggest mysteries in physics,” said Parmar.

Bombaci, Scordino and Parmar are now building on their recent study and trying to improve their stellar model. For instance, they plan to include more realistic white dwarf compositions and consider a wider range of dark matter properties.

“We also want to investigate how different amounts of dark matter could leave observable fingerprints, such as unusually faint supernovae or very light neutron stars, and compare these predictions with current and upcoming observations,” added the authors.

“In the longer term, we hope to connect our theoretical work more closely with multi‑messenger astronomy, using data from telescopes and gravitational‑wave detectors to test whether dark matter is truly shaping the lives and deaths of stars. In parallel, we aim to investigate whether low-mass neutron stars originating from ECSNe can provide new constraints on the neutron-star equation of state at the intermediate densities.”

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