The contribution of red dwarfs and white dwarfs to the halo dark matter

TL;DR

This study evaluates the combined impact of red and white dwarfs on galactic halo dark matter using simulations, concluding their contribution is less than 10%, insufficient to explain observed microlensing events.

Contribution

It provides a joint analysis of red and white dwarf contributions to halo dark matter using detailed Monte Carlo simulations and compares results with microlensing data.

Findings

Red dwarfs increase optical depth by a factor of 2 but remain insufficient.

White dwarfs alone cannot account for observed microlensing events.

Total contribution of studied populations is less than 10% of halo dark matter.

Abstract

The nature of the several microlensing events observed by the MACHO team towards the LMC still remains controversial. Low-mass substellar objects and stars with masses larger than ~1 M_{sun} have been ruled out as major components of a MACHO galactic halo, while stars of half solar masses are the most probable candidates. In this paper we assess jointly the relative contributions of both red dwarfs and white dwarfs to the mass budget of the galactic halo. In doing so we use a Monte Carlo simulator which incorporates up-to-date evolutionary sequences of both red dwarfs and white dwarfs as well as detailed descriptions of our Galaxy and of the LMC. We explore the complete mass range between 0.08 and 1 M_{sun} as possible microlensing candidates and we compare the synthetic populations obtained with our simulator with the results obtained by the MACHO and EROS experiments. Our results indicate that, despite that the contribution of the red dwarf population increases by a factor of 2 the value of the optical depth obtained when taking into account the white dwarf population alone, it is still insufficient to explain the number of events claimed by the MACHO team. Finally, we find that the contribution to the halo dark matter of the whole population under study is smaller than 10% at the 95% conficence level.