# Evolution of binary stars in the early evolutionary phases of ultra-faint dwarf galaxies

**Authors:** Alexander R. Livernois, Enrico Vesperini, Václav Pavlík  
**arXiv:** [2303.12841](https://arxiv.org/abs/2303.12841)  
**Date:** 2023-03-22  
**Summary page:** https://www.summarizepaper.com/en/paper/2303.12841v1/

## Key points

- Binary stars provide insight into the structure and dynamics of star clusters and galaxies
- $N$-body simulations were conducted to explore the evolution of binary stars in ultra-faint dwarf galaxies (UFD)
- Wide binaries are significantly disrupted during early evolutionary phases of UFD, leaving their dynamical fingerprints on surviving binaries' semi-major axis distribution
- An initially thermal eccentricity distribution is preserved except for the widest binaries which evolve towards a superthermal distribution
- Memory of an initially uniform eccentricity distribution is rapidly lost for most binaries as wider binaries evolve to approach a thermal/superthermal distribution
- The evolution of binaries is driven by tidal effects due to the potential of the UFD dark matter halo and collisional effects associated with binary-binary/single star encounters
- Collisional effects are particularly important within clumpy substructure characterizing the system during its early evolution; encounters may lead to exchanges between either primordial binary components or one interacting star.
- These simulations provide valuable insights into how binary stars evolve in ultra-faint dwarf galaxies during their early evolutionary phases, with implications for other astrophysical systems where binaries play an important role in shaping their dynamics.

## Summary

The study of binary stars provides a unique opportunity to gain insight into the structure and dynamics of star clusters and galaxies. In this paper, Alexander R. Livernois, Enrico Vesperini, and Václav Pavlík present the results of a set of $N$-body simulations aimed at exploring the evolution of binary stars during the early evolutionary phases of ultra-faint dwarf galaxies (UFD). The authors assume that the stellar component of the UFD is initially dynamically cold and evolves towards its final equilibrium after undergoing the violent relaxation phase. The authors show that during the early evolutionary phases of the UFD, wide binaries are significantly disrupted, leaving their dynamical fingerprints on the semi-major axis distribution of surviving binaries compared to models initially in equilibrium. An initially thermal eccentricity distribution is preserved except for the widest binaries which evolve towards a superthermal distribution. For a binary population with an initially uniform eccentricity distribution, memory of this initial distribution is rapidly lost for most binaries as wider binaries evolve to approach a thermal/superthermal distribution. The evolution of binaries is driven both by tidal effects due to the potential of the UFD dark matter halo and collisional effects associated with binary-binary/single star encounters. Collisional effects are particularly important within clumpy substructure characterizing the system during its early evolution; in addition to enhancing binary ionization and evolution of binary orbital parameters, encounters may lead to exchanges between either primordial binary components or one interacting star. Overall, these simulations provide valuable insights into how binary stars evolve in ultra-faint dwarf galaxies during their early evolutionary phases. The results highlight how disruptions can affect semi-major axis distributions and eccentricity distributions over time. These findings have implications for understanding not only ultra-faint dwarf galaxies but also other astrophysical systems where binaries play an important role in shaping their dynamics.