Experimental Limits on the Dark Matter Halo of the Galaxy from Gravitational Microlensing

MACHO Collaboration; C. Alcock; R. A. Allsman; T. S. Axelrod; D. P. Bennett; K. H. Cook; K. C. Freeman; K. Griest; J. A. Guern; M. J. Lehner; S. L. Marshall; H.-S. Park; S. Perlmutter; B. A. Peterson; M. R. Pratt; P. J. Quinn; A. W. Rodgers; C. W. Stubbs; W. Sutherland

doi:10.1103/PhysRevLett.74.2867

Experimental Limits on the Dark Matter Halo of the Galaxy from Gravitational Microlensing

C. Alcock, R. A. Allsman, T. S. Axelrod, D. P. Bennett, K. H. Cook, K. C. Freeman, K. Griest, J. A. Guern, M. J. Lehner, S. L. Marshall, H.-S. Park, S. Perlmutter, B. A. Peterson, M. R. Pratt, P. J. Quinn, A. W. Rodgers, C. W. Stubbs, and W. Sutherland (MACHO Collaboration)

Phys. Rev. Lett. 74, 2867 – Published 10 April 1995

Abstract

We monitored $8.6 \times 10^{6}$ stars in the Large Magellanic Cloud for 1.1 years and have found three events consistent with gravitational microlensing. We place strong constraints on Galactic halo lensing objects in the mass range $10^{- 4} M_{⊙}$ to $10^{- 1} M_{⊙}$ . Three events are fewer than expected for a standard spherical halo of objects in this mass range, but appear to exceed the number expected from known Galactic populations. Fitting a naive spherical halo model to our data yields a MACHO fraction $f$ of massive compact halo objects (MACHOs), ${f = 0.19}_{- 0.10}^{+ 0.16}$ , a total MACHO mass (inside 50 kpc) of ${7.6}_{- 4}^{+ 6} \times 10^{10} M_{⊙}$ , and a microlensing optical depth ${8.8}_{- 5}^{+ 7} \times 10^{- 8}$ (68% C.L.).

Received 23 January 1995

DOI:https://doi.org/10.1103/PhysRevLett.74.2867

Authors & Affiliations

C. Alcock^1,2, R. A. Allsman³, T. S. Axelrod^1,4, D. P. Bennett^1,2, K. H. Cook^1,2, K. C. Freeman⁴, K. Griest^2,5, J. A. Guern^2,5, M. J. Lehner^2,5, S. L. Marshall^2,6, H.-S. Park¹, S. Perlmutter², B. A. Peterson⁴, M. R. Pratt^2,6, P. J. Quinn⁴, A. W. Rodgers⁴, C. W. Stubbs^2,6,7, and W. Sutherland^2,8 (MACHO Collaboration)

¹Lawrence Livermore National Laboratory, Livermore, California 94550
²Center for Particle Astrophysics, University of California, Berkeley, California 94720
³Supercomputing Facility, Australian National University, Canberra, A.C.T. 0200, Australia
⁴Mount Stromlo and Siding Spring Observatories, Australian National University, Weston, A.C.T. 2611, Australia
⁵Department of Physics, University of California, San Diego, California 92093
⁶Department of Physics, University of California, Santa Barbara, California 93106
⁷Departments of Astronomy and Physics, University of Washington, Seattle, Washington 98195
⁸Department of Physics, University of Oxford, Oxford OX1 3RH, United Kingdom