Double Neutron Star systems: origin and demographics

• Grant number: 25/01641-7
• Support Opportunities: Scholarships in Brazil - Master
• Start date: April 01, 2025
• End date: November 30, 2026
• Field of knowledge: Physical Sciences and Mathematics - Astronomy - Stellar Astrophysics
• Principal Investigator: Jorge Ernesto Horvath
• Grantee: Bianca Bulhões Martins
• Host Institution: Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 24/16892-2 - Compact Star populations in the galaxy and the Cosmos, AP.R

Abstract

We know little about DNS as a subset of the neutron star population in general. The formation channel hypothesized to produce the systems that were known (Fig. 2, left [3]) has a massive giant and another Main Sequence companion in a stable mass transfer process that brings the system into a common envelope after the more massive one explodes as a supernova and forms the first neutron star. This stage, important for evolution, is very difficult to measure and model and remains almost completely unknown. However, it is responsible for circularizing the orbit and when the companion evolves into its helium star stage (that is, without a hydrogen envelope), it leads to another stable mass transfer stage that culminates in the second explosion.However, a second channel has been brought into discussion (Fig.2, right [3]) which starts with two post-MS stars exchanging mass in an unstable manner and also by a common envelope stage, this time with two helium cores, which also allows for successive explosions and a double system without necessarily leading to equal masses or completely circular orbits. The kick imparted to the NS by supernovae in each case needs to be small, as there is a risk of disruption if it is too large. We immediately realized that there are variants to be discussed, for example, the concrete possibility that one of the two progenitor stars corresponds to the band that produces O-Mg-Ne lumps and not "iron", and several questions regarding the mass transfer stages and the common envelope.The DNS mass ratio is different depending on the formation channel. This asymmetry plays an important role in the evaluation of fusions and nucleosynthesis in general.