# Effect of spin on the inspiral of binary neutron stars

## TL;DR

This study uses long-term simulations to analyze how spin influences the inspiral phase of binary neutron stars, revealing that spin effects can surpass tidal effects at moderate spins.

## Contribution

It provides the first detailed comparison showing spin effects can dominate over tidal effects in binary neutron star inspirals at moderate spin levels.

## Key findings

- Spin effects can be larger than tidal effects in phase evolution.
- Tidal effects dominate only at very small spins (≤0.1).
- Spin influence increases with higher spin magnitudes.

## Abstract

We perform long-term simulations of spinning binary neutron stars, with our highest dimensionless spin being $\chi \sim 0.32$. To assess the importance of spin during the inspiral we vary the spin, and also use two equations of state, one that consists of plain nuclear matter and produces compact stars (SLy), and a hybrid one that contains both nuclear and quark matter and leads to larger stars (ALF2). Using high resolution that has grid spacing $\Delta x\sim 98$ m on the finest refinement level, we find that the effects of spin in the phase evolution of a binary system can be larger than the one that comes from tidal forces. Our calculations demonstrate explicitly that although tidal effects are dominant for small spins ($\lesssim 0.1$), this is no longer true when the spins are larger, but still much smaller than the Keplerian limit.