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Dark matter and stars Malcolm Fairbairn. Hertzsprung-Russell (luminosity-temperature) Diagram.

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Presentation on theme: "Dark matter and stars Malcolm Fairbairn. Hertzsprung-Russell (luminosity-temperature) Diagram."— Presentation transcript:

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 where dark matter forms thermal core within the star of radius annihilation rate inside the core given by and equilibrium is reached whenNumber in core evolves as See e.g. Griest and Seckel 1988

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

6 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 Possible enhancement at the centre of the galaxy due to 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  10 GeV cm 8 -3

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

9 Central nuclear energy generation rates PP CNO 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 temperature luminosity Bottom of HR diagram in Globular Cluster M4

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

17 Dark matter density profile in globular cluster

18 Gravitational heating of dark matter in globular cluster

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

20 Heating of neutron stars as a function of galactic radius

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

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 assume capture rate of  (100 GeV / m)/s and neutron star temperature of 10 K 295

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

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

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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