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MACHO Project Limits on Black Hole Dark Matter in the 1-30 Solar Mass Range

The Macho collaboration, C. Alcock, R. A. Allsman, D. R. Alves, T. S. Axelrod, A. C. Becker, D. P. Bennett, K. H. Cook, N. Dalal, A. J. Drake, M. Geha, K. Griest, M. J. Lehner, S. L. Marshall, D. Minniti, C. A. Nelson, B. A. Peterson, P. Popowski, M. R. Pratt, P. J. Quinn, C. W. Stubbs, W. Sutherland, A. B. Tomaney, T. Vandehei, D. L. Welch

TL;DR

The paper investigates whether high-mass compact objects in the range $0.3\,M_\odot$ to $30\,M_\odot$ can constitute the Milky Way's dark halo. It employs a long-duration microlensing search toward the Large Magellanic Cloud using the MACHO dataset, enforcing ${\widehat{t}}>150$ days, computing detection efficiency with blending, and modeling the halo with Model S. No long-duration microlensing events are observed; at 95% c.l., such objects cannot make up 100% of the halo, and for $m<10\,M_\odot$ the allowed halo fraction is $<40\%$, with halo mass normalization considerations placing quantitative limits (e.g., $4\times 10^{11} M_\odot$ within 50 kpc for certain mass ranges). The results strengthen constraints on compact dark matter candidates in the high-mass window and highlight the dependence on halo normalization, noting that full 8-year data analysis may extend the limits or reveal rare long-duration events.

Abstract

We report on a search for long duration microlensing events towards the Large Magellanic Cloud. We find none, and therefore put limits on the contribution of high mass objects to the Galactic dark matter. At 95% confidence level we exclude objects in the mass range 0.3 solar masses to 30.0 solar masses from contributing more than 4 times 10^11 solar masses to the Galactic halo. Combined with earlier results, this means that objects with masses under 30 solar masses cannot make up the entire dark matter halo if the halo is of typical size. For a typical dark halo, objects with masses under 10 solar masses contribute less than 40% of the dark matter.

MACHO Project Limits on Black Hole Dark Matter in the 1-30 Solar Mass Range

TL;DR

The paper investigates whether high-mass compact objects in the range to can constitute the Milky Way's dark halo. It employs a long-duration microlensing search toward the Large Magellanic Cloud using the MACHO dataset, enforcing days, computing detection efficiency with blending, and modeling the halo with Model S. No long-duration microlensing events are observed; at 95% c.l., such objects cannot make up 100% of the halo, and for the allowed halo fraction is , with halo mass normalization considerations placing quantitative limits (e.g., within 50 kpc for certain mass ranges). The results strengthen constraints on compact dark matter candidates in the high-mass window and highlight the dependence on halo normalization, noting that full 8-year data analysis may extend the limits or reveal rare long-duration events.

Abstract

We report on a search for long duration microlensing events towards the Large Magellanic Cloud. We find none, and therefore put limits on the contribution of high mass objects to the Galactic dark matter. At 95% confidence level we exclude objects in the mass range 0.3 solar masses to 30.0 solar masses from contributing more than 4 times 10^11 solar masses to the Galactic halo. Combined with earlier results, this means that objects with masses under 30 solar masses cannot make up the entire dark matter halo if the halo is of typical size. For a typical dark halo, objects with masses under 10 solar masses contribute less than 40% of the dark matter.

Paper Structure

This paper contains 4 sections, 2 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Data
  3. New Analysis
  4. Discussion

Figures (3)

  • Figure 1: Microlensing detection efficiency for the 5.7-year MACHO data, as a function of event timescale ${\widehat{t}}\,$. The solid line shows the photometric efficiency computed for cut set A, with the additional constraint that ${\widehat{t}}\,>150$ days. The dashed line (from A2000a) is the same but without the additional constraint.
  • Figure 2: Number of long duration events expected vs. lens mass for halo model S. The dashed lines drawn at $N=3$ and $N=4.6$ indicate the 95% c.l. and the 99% c.l. limit respectively. Masses above these lines are ruled out at their respective confidence limits.
  • Figure 3: Halo fraction upper limit as a function of lens mass for model S. The region above the line is ruled out at 95% c.l. This model contains $4 \times 10^{11} { \rm \, M_\odot}$ within 50 kpc, so a less model dependent result can be found by reading the ordinate as "Halo mass in MACHOs/($4 \times 10^{11} { \rm \, M_\odot}$)".