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Dark matter and stars

Explore the fascinating relationship between dark matter and stars, as revealed through the Hertzsprung-Russell diagram. Discover how dark matter forms thermal cores within stars and its effect on their evolution. Dive into simulations predicting high densities in the center of the galaxy and the potential enhancement caused by black holes. Uncover the mysteries surrounding WIMP burning stars and the impact of dark matter on neutron stars. Find out how the accretion of dark matter onto stars can shape the nature of these celestial objects.

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Dark matter and stars

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  1. Dark matter and stars Malcolm Fairbairn

  2. Hertzsprung-Russell (luminosity-temperature) Diagram

  3. Hertzsprung-Russell diagram from computer

  4. Capture of dark matter onto stars capture rate See e.g. Griest and Seckel 1988 where dark matter forms thermal core within the star of radius annihilation rate inside the core given by Number in core evolves as and equilibrium is reached when

  5. Dark matter density For bigger effect, need bigger density Simulations predict high densities in the centre of the galaxy and baryonic contraction plus the black hole may increase this. M. Gustafsson, M.F. and J. Sommer-Larsen

  6. Possible enhancement at the centre of the galaxy due to black hole Gondolo and Silk 1999 Bertone and Merritt 2005 = mass density of dark matter particles in phase space Diffusion in mom. space due to gravitational heating by stars DM self annihilation and actual collisions with stars DM falling into Black hole

  7. Solution of diffusion equation show that initial spikes die down over time Bertone and Merritt 2005 we find interesting things start to happen around r = 10 GeV cm 8 -3

  8. Effect of composition on capture Also need to take into account chemical composition of star For the solar composition, this yields extra factor 216

  9. Central nuclear energy generation rates CNO PP WIMP burning stars

  10. Effect of WIMP accretion onto low mass stars ‘break’ seems to get bigger and move higher with density

  11. Eckart and Genzel

  12. 200 x 275 pc distance 8500 pc

  13. What about increasing escape velocity? White dwarves - high escape velocity - born hot NEED TO FIND SOME OLD ONES

  14. White Dwarves in Globular Cluster M4 Richer et al. 2004

  15. Bottom of HR diagram in Globular Cluster M4 luminosity temperature

  16. Need to work out density of dark matter in globular cluster Colafrancesco et al. Astro-ph/0507575

  17. Dark matter density profile in globular cluster

  18. Gravitational heating of dark matter in globular cluster

  19. Wimp burning white dwarves in globular clusters MF and G.Bertone, in preparation

  20. Heating of neutron stars as a function of galactic radius

  21. CHANDRA image of galactic centre in x-rays lots of neutron stars! Easier to find hot neutron stars than cooler ones, but we need the cooler ones to constrain WIMPS.

  22. Fate of Neutron star close to the centre of the galaxy excluded - unitarity

  23. Fate of Neutron star close to the centre of the galaxy excluded - unitarity self gravitating 29 5 • assume capture rate of G = 10 (100 GeV / m)/s and neutron star temperature of 10 K

  24. Fate of Neutron star close to the centre of the galaxy excluded - unitarity degenerate self gravitating

  25. Fate of Neutron star close to the centre of the galaxy excluded - unitarity black hole degenerate self gravitating

  26. Conclusions • accretion of dark matter onto stars can in principle seriously affect their nature • white dwarfs already place interesting constraints on dark matter scenarios • neutron stars can in principal rule out many more exotic dark matter scenarios

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