The Formation of Electron-capture Supernovae: A Review

TL;DR

EC-SNe result from electron captures in degenerate ONe cores near $M_{ m Ch}$, forming neutron stars with typically low explosion energies. The paper surveys two main formation channels—the single-star channel (super-AGB and He stars) and the binary channel (He-star binaries and accretion-induced collapse in WD binaries)—and discusses progenitor ranges, evolutionary paths, candidates, and observational constraints, including how EC-SNe differ from ultra-stripped SNe. It highlights implications for neutron-star birth masses, the double NS population, and specific nucleosynthesis signatures (notably neutron-rich isotopes and r-process elements), and emphasizes the need for multidimensional modeling and multi-wavelength observations to robustly identify EC-SNe. The review also outlines outstanding theoretical uncertainties (e.g., dredge-up efficiency, flame propagation, and reaction rates) and presents future prospects with upcoming surveys and facilities.

Abstract

It is generally believed that the electron-capture reactions happen when the oxygen-neon (ONe) cores grow in masses close to the Chandrasekhar limit, leading to the formation of neutron stars (NSs) via electron-capture supernovae (EC-SNe). EC-SNe are predicted to be the most likely short-lived and faint optical transients, and a small ejecta mass is expected during the collapse. This kind of SNe provide an alternative channel for producing isolated NSs and NS systems, especially for the formation of X-ray binaries and double NSs. Although EC-SNe were proposed ~45 yr ago, there are still some uncertainties for the origin of EC-SNe. In this article, we review recent studies on the two classic progenitor channels of EC-SNe, i.e., the single star channel and the binary star channel. In the single star channel, EC-SNe can happen in super asymptotic giant branch stars or He stars, whereas in the binary star channel EC-SNe can occur in He stars in binaries (involving He star+MS systems and NS+He star systems) or accretion-induced collapse in white dwarf binaries (involving the single-degenerate scenario and the double-degenerate scenario). Recent progress on the two progenitor channels is discussed, including the initial parameter range for EC-SNe, the evolutionary paths to EC-SNe, related objects and some observational constraints, etc. We also make some discussions on the possible candidates for EC-SNe in this article, and the impacts of EC-SNe on some research fields, e.g., the properties of NSs, double NS population and chemical products, etc. We also discuss the differences between EC-SNe and ultra-stripped SNe in this article. Research on EC-SNe is at a pivotal stage, with key theoretical uncertainties and observational challenges requiring integrated modeling and multi-wavelength observations for robust identification.

Figures (8)

• Figure 1: Evolutionary channel flowchart for the formation of EC-SNe.
• Figure 2: A super-AGB star and its degenerate ONe core that is supported by electron pressure. When the ONe core has mass close to $M_{\rm Ch}$, electron-capture reactions on $^{24}\rm Mg$ and $^{20}\rm Ne$ happen. ln this process, Na and F are also formed along with lots of neutrinos.
• Figure 3: Evolutionary scenarios for the formation of He star+MS systems, in which the He star could form an EC-SN (see also Tauris2006csxs.book..623T2018AA...614A..99S).
• Figure 4: The mass-transfer rate in the Case A system varies over time, exhibiting three clearly defined stages. The left panel illustrates the mass-transfer rate throughout the central H-burning stage. The middle panel displays the rates during H-shell burning stage, while the right panel presents the mass-transfer behavior during and following the carbon-burning stage. Source: From 2017ApJ...850..197P.
• Figure 5: Kippenhahn diagram of a $2.67\,M_\odot$ He star companion from He-ZAMS to electron-capture reactions, including the evolution of interior structure and energy production (for the details of this evolution see Guo2024MNRAS.530.4461G). The hatched regions denote convection caused by the He-, C-, and advanced burning phases. The blue regions indicate the convection regions. The intensity shown in the color-bar represents the nuclear energy-production rate.