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  • Open Access

Robust bounds on MACHOs from the faintest galaxies

Peter W. Graham1,2,*, Harikrishnan Ramani3,†, and Maximilian Ruhdorfer1,‡

  • 1Leinweber Institute for Theoretical Physics at Stanford, Department of Physics, Stanford University, Stanford, Califonria 94305, USA
  • 2Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics, Stanford University, Stanford, California 94305, USA
  • 3Department of Physics and Astronomy and the Bartol Research Institute, University of Delaware, Newark, Delaware 19716, USA

  • *Contact author: pwgraham@stanford.edu
  • †Contact author: hramani@udel.edu
  • ‡Contact author: m.ruhdorfer@stanford.edu
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Phys. Rev. D 113, 023047 – Published 23 January, 2026

DOI: https://doi.org/10.1103/2dv9-xxtw

Abstract

We use the dynamical heating of stars in ultrafaint dwarf (UFD) galaxies to set limits on Massive Compact Halo Objects (MACHOs). In our analysis we study the robustness of the bounds under uncertainties in key UFD parameters, such as the half-light radius, stellar velocity dispersion, total halo mass and dark matter and stellar density profiles. We apply this framework to both well-established UFD candidates, as well as the recently discovered UFD candidate Ursa Major III/UNIONS 1. We find that multiple UFDs yield consistently strong limits in the mass range 10M⊙≲MMACHO≲109M⊙, underscoring the robustness of a previous analysis solely based on Segue I. We also demonstrate that Ursa Major III, if confirmed as an UFD, would improve the constraints significantly, providing the strongest constraints on MACHO dark matter in the mass range 1M⊙≲MMACHO≲105M⊙.

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Phys. Rev. D 113, 023047– Published 23 January, 2026
  • Received 13 November 2025
  • Accepted 2 January 2026
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