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Neutron Stars as Cosmological Laboratories of Dark Matter

Neutron Stars as Cosmological Laboratories of Dark Matter. Shmulik Balberg, The Hebrew University. in collaboration with G. Farrar (NYU). Outline:. Dark matter microphysics – A renaissance. Possible constraints from neutron stars on. “active” dark matter . “passive” dark matter.

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Neutron Stars as Cosmological Laboratories of Dark Matter

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  1. Neutron Stars as Cosmological Laboratories of Dark Matter Shmulik Balberg, The Hebrew University in collaboration with G. Farrar (NYU)

  2. Outline: • Dark matter microphysics – A renaissance • Possible constraints from neutron stars on • “active” dark matter • “passive” dark matter

  3. (Most of the) Dark matter is … • … (probably) COLD (nonrelativistic at decoupling) • … very hard to detect… • … ? • … not in compact objects (MACHO search) • … not in planets or brown dwarfs • … not in uncondensed gas …Nonbaryonic at all!(*) (Big Bang Nucleosynthesis, CMB anisotropies)

  4. Dark matter candidates: 1999 • axions, neutralinos (~ interaction free) 2000 Observational motivation for interacting dark matter (Spergel & Steinhardt, PRL 84, 3760 (2000)) Self-interacting, mirror, warm, annihilating, multicomponent, fuzzy, fluid, decaying…… (See Ostriker & Steinhardt, SCIENCE 2003)

  5. “Active” Dark Matter i.e. Forms in neutron stars through chemical equilibrium: Equation of State P(e) M, R, I, Wmax • n-emissivity  thermal history • Bulk viscosity  R-modes • electric conductivity  magnetic field evolution • proto-NS evolution  NS-black hole connection

  6. Active dark matter candidates • stable strange quark matter • A light stable dibaryon (H) Ruled out! (EoS too soft – Glendenning & Schaffner-Bielich 1998) • A light stable supersymmetric baryon (S0) Certainly possible! (Mmax1.7-1.8M) due to strong repulsive interactions (Balberg, Farrar & Piran 2001)

  7. Axions rapid cooling? n+nn+n+A; LAT6 (limits Axion-nucleon coupling) (Iwamoto 1984) • ……

  8. “Passive” Dark Matter i.e. cannot form in neutron stars is accreted from environment: Condensation in NS  destabilize • heating by in bulk or near surface annihilation • direct observation of excess high energy photons/neutrinos

  9. How WIMPs destabilize a neutron star(Goldman and Nussinov 1989) • WIMPs accrete onto the neutron star • WIMPs thermalize and condense to a thermal radius, (GM/Rth)v2 • WIMPs become self-gravitating when MX(Rth)>Mbar(Rth) • Self-gravitating WIMPs might collapse to a black hole GN89: WIMPS – dM/dt100 gm sec-1 For Tc=105°K, MBH1018gm, sWN~10-38 cm2Neutron stars live tNS<109yrs

  10. To be more specific: need very cold star T105 K Marginal (unless Bose-Einstein condensation accelerates collapse to a black hole)

  11. Accumulate a self-gravitating WIMP mass (Balberg and Farrar in prep) • BF03 – if sWN0, gravitational relaxation (+ dynamical friction): no fixed “Rth” Work in Progress…. sWN~0 Bosonic WIMPs are excluded! • dM/dt for interacting DM: ~104-105gm/sec Collapse depends on WIMP and WIMP-N interactions

  12. Summary: Neutron star theory and observation may be useful for constraining dark matter candidates Examples: • A light bosonic baryon must have ~0 attractive component • Bosonic WIMPs with sWN~0 destabilize old neutron stars – ruled out?

  13. kBT~(GMX/Rth) rbar1015 gm/cm3 Accumulate a self-gravitating WIMP mass (I) • accretion rate (dM/dt) GS89: non-interacting - ~100gm/sec • relaxation velocity GS89: thermalize with nucleons kBT - ~105K • Self-gravitating mass GS89: MX=4p/3(Rth)3rbar

  14.  Dark matter halos

  15. Equilibrium composition of dense matter • “soup” of nucleons, leptons, other particles • local charge neutrality (r+=r-) • chemical equilibrium to weak interactions, e.g., • np+e ; mn=mp+me • evolved neutron stars: no n’s, T=0

  16. WIMP induced instability of a neutron star (Goldman and Nussinov 1989)

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