Astrophysical observations preferring Modified Gravity

Transcription

1 Astrophysical observations preferring Modified Gravity A natural approach to extended Newtonian gravity: tests and predictions across astrophysical scales. Mon.Not.Roy.Astron.Soc. 411 (2011) Wide binaries as a critical test of Classical Gravity. arxiv: [astro-ph.ga] The outskirts of globular clusters as modified gravity probes. arxiv: [astro-ph.co] Cosmology on the Beach Cancun, Mexico 20th January, 2012 Juan Carlos Hidalgo

2 Where is Dark Matter required? Galactic rotation curves. Gravitational lensing and dynamics of clusters. Cosmological matter fraction requirements. 1M 1000 M 106 M 109 M M

3 Where is gravity tested? Solar System dynamics Terrestrial experiments Particle accelerators 10 3 pc 10 pc 1000 pc 10 kpc 10 Mpc

4 Room for alternatives Modified Dynamics below a 0 = m/sec 2 (MoND) a a 0. a = a N, a a 0 = a a 0. a = (a 0 a N ) 1/2, a a 0 = ( GM, ( ) 1/2 GM a 0 r, 2 a 0 r 2 ) NGC 6946 NGC 1560

5 log(a/a0) Astrophysical systems with a a 0 log(size/1kpc)

6 Extended Gravity Modified gravity below a 0 Define x ( GM a 0 r 2 ) 1/2 g/a 0 = f (x) g a 0, x g = g N, g a 0, x 0 g = (a 0 g N ) 1/2, General Interpolation Function g = x 2, a 0 g = x, a 0 g/a 0 = f (x) = x 1 xn+1 1 x n, n 1.

7 Check-ups of modified gravity Newton s Theorems No net force from outer shells δm 1 /δm 2 = ρr 2 1δΩ 1 /ρr 2 2δΩ 2 = r 2 1/r 2 2 ( ) k δm1 = δm 2 ( ) 2k r1 r 2 Accurate description of systems with spherical symmetry Predictions for the outer radii of galactic systems

8 Scaling laws in Equilibrium configurations Tully-Fisher, Faber-Jackson and Fundamental Plane relations Equilibrium Condition ˆP kin = ρ(r)σ 2 (r) = g(r) = a 0 f (x) r ˆP kin Kinetic pressure per unit mass. σ(r) isotropic dispersion velocity (pressure supported sys.) rotation velocity (angular momentum supported sys.) Phenomenological description: σ 2 (r) = Cr β M(r) γ.

9 Scaling laws in Equilibrium configurations (Mendoza++,11) (Hernandez++,10) Equilibrium Condition ˆP kin = ρ(r)σ 2 (r) = g(r) = a 0 f (x) r Theoretical prescription: σ 2 (r) =Cr β M(r) γ 1/2 1 x4 = (GMa 0 ) 1 x 3 β = 2 4γ = { 1/2 if g a 0 ; 0 if g a 0. Fundamental plane + Tully-Fisher + Faber-Jackson + Scaling law for dsph.

10 Probes for gravity

11 log(a/a0) New probes for gravity log(size/1kpc)

12 Scaling law for Globular Clusters (Scarpa++,07) Keplerian fall not observed

13 Modified Dynamics for Globular Clusters (Scarpa++,11)... Keplerian fall not observed

14 Scaling law for Globular Clusters (Hernandez+Jimenez,11) Keplerian fall not observed A Faber-Jackson-like scaling law σ/σ 0 = (M/M ) 1/4

15 Stability criterion Projected velocity of wide binaries Tidal stability of binaries under the galactic field (Jiang+Tremaine,10) df gal dr r = F int = GM 2 sat/ r 2 r Separation of binary stars M sat Mass of binary stars ρ sat (4π/3)M sat ( r) 3

16 Stability criterion Projected velocity of wide binaries Modified gravity signature (Hernandez++,11) df gal dr r = F int = GM 2 sat/ r 2 Newtonian stability for the system ρ sat > ρ, ( v ( r) 1/2 ) Under modified gravity ρ sat > ( r/r) ρ, ( v = const.)

17 Modified (Extended) Gravity Features Valid and testable theory (e.g. no dark matter above a 0 ). Consistent description of galactic dynamics. Sensible explanation of phenomena in binary systems and globular clusters where no DM is expected. Shortcomings No covariant relativistic counterpart to account for lensing or cosmology. No easy prescription for a universal gravitational potential (no simple n-body simulations). Description of Galaxy Clusters requires neutrino dark matter.

18 Astrophysical observations preferring Modified Gravity A natural approach to extended Newtonian gravity: tests and predictions across astrophysical scales. Mon.Not.Roy.Astron.Soc. 411 (2011) Wide binaries as a critical test of Classical Gravity. arxiv: [astro-ph.ga] The outskirts of globular clusters as modified gravity probes. arxiv: [astro-ph.co] Christine Allen Tula Bernal Xavier Hernandez Alejandra Jimenez Sergio Mendoza Juan Carlos Hidalgo Cosmology on the Beach Cancun, Mexico 20th January, 2012