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ILOA Galaxy Forum Europe 2013 - dark matter in galaxies - dr benoit famaey

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ILOA Galaxy Forum Europe 2013 - dark matter in galaxies - dr benoit famaey

  1. 1. Dark Matter in galaxies !Refining the free function of MOND B. Famaey (Strasbourg Observatory, France)
  2. 2. Large-Scale « Geography » of the whole world •  Earth: diameter = 13 000 km, distance from Sun = 149 millions km (= 1 Astronomical Unit) •  Distance Earth-Mars between 0.4 and 2.7 A.U. •  c = 300 000 km/s (7.5 revolutions around the Earth in 1 second) •  Moon = 1.3 light-second •  Sun = 8 light-minutes •  Solar System = 6 light-hours •  Closest star (Proxima Centauri) = 4.2 light-years
  3. 3. The Milky WayOur Galaxy Sun’s(artist view) neighbourhood1011 stars 100 000 ly
  4. 4. Everything is in motion •  Earth goes around the Sun at 30 km/s •  Sun rotates at 220 km/s with respect to the center of the Milky Way (one orbit each 200 million years = Sun aged of ~25 galactic « years ») •  Milky Way moves at 600 km/s with the Local Group w.r.t. the Hubble flow •  Universe expands
  5. 5. Gravitation •  Newton (1686) : F = G m1 m2/ r2 •  Newton (1686): a = F/m •  Equivalence principle: inertial mass IS gravitational charge  General Relativity (Einstein, 1915), gravitation is notreally a force, just a deformation of space-time, natural stateis free-fall (like astronauts in space stations) •  Weakest « force » of Nature, but only one acting at long ranges (no screening) = governs the dynamics of the Universe on large scales
  6. 6. Equivalence principle
  7. 7. The old missing mass problem •  1781: William and Caroline Herschel discover Uranus •  1792: Delambre publishes orbit of Uranus, non-Newtonian even after taking the perturbations of other planets into account •  1834: Hussey proposes new planet, Airy believes in new •  1859: perihelion precession of gravitational law Mercury of 43 arcsec per•  1846: Le Verrier calculates the century, Leverrier postulates the position of the new planet existence of the small planet Vulcan Galle discovers Neptune But correct answer for Mercury found by Einstein in 1915
  8. 8. The modern-day missing mass •  1933: Zwicky observes •  End of the 1970s: Bosma velocity dispersion of and Rubin: 21 cm line of HI individual galaxies in the allows them to measure the Coma cluster, and finds asymptotically FLAT M/Mvis ≈ 20 rotation curves instead of Keplerian 1/√r falloff Doppler Shift: (λ-λ0)/λ0 = Vr / c
  9. 9. •  Not only the amplitude but the shape is abnormal: Vc = cste = M(r) ∝ r •  M( r ) = ∫ 4 π r2 ρ(r) dr = ρ(r) ∝ r -2 •  BUT ρvis(r) ∝ e-r/r0 /r
  10. 10. Dark Matter halo =85% to 95% of the mass
  11. 11. The Large Scale Structure
  12. 12. The ΛCDM model of the Universe - Cosmic Microwave Background at 2.7 K (Planck), variations of 1/100 000= 85% of the matter is dark … + accelerated expansion (dark energy)
  13. 13. Direct detection? Many experiments such as XENON100 (liquid Xenon) or Cryogenic Dark Matter Search (CDMS): try to detect a direct collision between a dark particle and a nucleus in a Germanium-Silicium crystal = NO LUCK… but can exclude certain masses and «   cross- sections »
  14. 14. Could gravitation also be wrong? …. Maybe… •  Gravitational acceleration at the edge of galaxies is 100 billion times smaller than on earth! = impossible to test in the lab! •  Direct relation between distribution of dark and normal matter in galaxies = unexplained!
  15. 15. Tidal dwarf galaxies Tidal dwarf galaxies in the NGC 5291 system Bournaud et al. (2007) Gentile, Famaey et al. (2007)
  16. 16. Milky Way and Andromeda: disks of satellites Milky Way Andromeda Kroupa et al. (2010) Ibata et al. (2013)
  17. 17. Conclusion •  Whatever the solution to the dark matter problem, it will lead us to one of the biggest revolutions in physics •  Either new particles, or new law of gravitation, or some subtle combination of both (if I had to bet I’d bet on the 3rd, but Nature does not care about anyone’s bet…) We should not consider the present favoured cosmologicalmodel as a dogma, but should also not discard it for purelyaesthetical personal reasons. On large scales, a plethora of dataare supporting it, on galaxy scales, we do not understand what ishappening = In Science, experiment is the ultimate judge! Not one’sown intuition or « preference »… Exciting future 