Are there MACHOs in the Milky Way halo?

Abstract

Microlensing searches aim to detect compact halo dark matter via its gravitational lensing effect on stars within the Large Magellanic Cloud. The most recent results have led to the claim that roughly one fifth of the galactic halo dark matter may be in the form of compact, solar-mass objects. We analyze this hypothesis by considering the goodness-of-fit of the best-fit halo dark matter solutions to the observational data. We show that the distribution of the durations of the observed microlensing events is narrower than that expected to result from a standard halo lens population at 90 to 95% confidence. Only when the fraction of expected background (non-halo) events is significantly increased does the discrepancy between the observed and theoretical event duration distributions disappear. This indicates that it is possible that most of the lenses responsible for the observed microlensing events are not located within the Milky Way halo.