On the Reported Death of the MACHO Era

TL;DR

This study uses radial velocity measurements of wide halo binaries to evaluate the viability of MACHO models for dark matter, confirming some candidates and questioning previous constraints.

Contribution

It provides new radial velocity data for wide halo binaries and critically reassesses MACHO constraints based on these binaries.

Findings

Confirmed three wide halo binaries as genuine.

Identified one spurious binary candidate.

Re-evaluated MACHO constraints, casting doubt on previous limits.

Abstract

We present radial velocity measurements of four wide halo binary candidates from the sample in Chaname & Gould (2004; CG04) which, to date, is the only sample containing a large number of such candidates. The four candidates that we have observed have projected separations >0.1 pc, and include the two widest binaries from the sample, with separations of 0.45 and 1.1 pc. We confirm that three of the four CG04 candidates are genuine, including the one with the largest separation. The fourth candidate, however, is spurious at the 5-sigma level. In the light of these measurements we re-examine the implications for MACHO models of the Galactic halo. Our analysis casts doubt on what MACHO constraints can be drawn from the existing sample of wide halo binaries.