Dark Matter Heats Up in Dwarf Galaxies

  • Speaker
  • Justin Read, Ph.D.Head of Physics, University of Surrey
Date & Time


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On large scales, the standard cosmological model provides a remarkable description of the universe. On small scales inside dwarf galaxies, however, long-standing tensions exist. Simulations of the universe’s formation that model only the dark-matter fluid overpredict the number of dwarf galaxies, known as the ‘missing satellites problem.’ The simulations also predict that these dwarfs should reside inside dark matter halos with steeply rising central density ‘cusps,’ whereas observations favor constant density dark matter ‘cores.’ This discrepancy is known as the ‘cusp-core problem.’ These problems could point to dark matter being more complex than initially thought. For example, dark matter could be weakly relativistic (‘warm’ dark matter) or self-interact via a new force in the dark sector (‘self-interacting’ dark matter). A simpler solution is that numerical models that model only the dark-matter fluid are missing some important physics.

In this talk, Justin Read will show how repeated gas cooling and heating during star formation causes the gravitational potential at the centers of dwarf galaxies to continually fluctuate. This kinematically ‘heats’ the dark matter, slowly pushing it out from the centers of the dwarfs. He will present the first observational evidence for this process occurring in a sample of 18 nearby dwarf galaxies and will show how this solves both the cusp-core and missing satellites problems. He will conclude with a discussion of the broader implications of these results and how these dwarfs can now be used to place competitive constraints on alternative dark matter models.

About the Speaker

Read completed his Ph.D. in theoretical astrophysics at Cambridge University in 2004. After a two-year postdoctoral research position in Cambridge, he moved to the University of Zürich to join the computational science group. In 2009, he joined the University of Leicester as a lecturer in theoretical astrophysics. In October 2010, he was awarded an SNSF assistant professorship at ETH Zürich. In April 2013, he moved to the University of Surrey to set up their new astrophysics program, and in 2018 he became head of the physics department. His main area of research is in gravitational probes of dark matter, studying everything from the tiniest galaxies to giant clusters of galaxies. Read was awarded the 2013 MERAC Prize by the European Astronomical Society for his high-impact research in computational astrophysics and cosmology. He is a fellow of the Institute of Physics and the Royal Physiographic Society of Lund.

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