2012. ASTRO SUMMER SCHOOL. DARK MATTER & GALACTIC ROTATION. In 1933, Fritz Zwicky calculated the mass of the Coma Cluster. More evidence was discovered by Vera Rubin who measured the rotation curves of many galaxies during the 1970s. The expected distribution of dark matter in the Milky Way.
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ASTRO SUMMER SCHOOL
DARK MATTER & GALACTIC ROTATION
In 1933, Fritz Zwicky calculated the mass of the Coma Cluster
More evidence was discovered by Vera Rubin who measured the rotation curves of many galaxies during the 1970s.
The expected distribution of dark matter in the Milky Way
Cosmic Microwave Background (CMBR)
CMBR Power Spectrum
The first peak gives us information about the curvature of the Universe.
The ratio of the odd peaks to the even peaks gives us the baryon density.
The third peak tells us about the density of dark matter.
We can alter the cosmological parameters so that the curve fits the observed data.
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Dark Matter – Then and Now
The Bullet Cluster
More evidence for dark matter
Velocity dispersion of galaxies
Measurements of the velocities of galaxies within clusters.
Periodic fluctuations in baryonic matter caused by acoustic waves in the early Universe.
Type Ia supernovae measurements
Put a limit on the amount of dark energy hence constrain dark matter
If the Big Bang model is correct, dark matter is required to allow structures to form.
A solid body (i.e. a disk) will have a rotational velocity that is proportional to distance – as R increases, v increases.
Since , for objects that are gravitationally bound (i.e. not a solid disk), we expect v to be proportional to
Galaxies do not follow Keplerian rotation, outside of the core of the galaxy, v is approximately constant. This provides evidence for dark matter.
Galactic rotation curves
Cryogenic detector experiments
Cryogenic detectors, operating at temperatures below 100mK, detect the heat produced when a particle hits an atom in a crystal absorber such as germanium.
CRESST, Gran Sasso, Italy
CDMSII, Soudan Mine, Minnesota
Noble liquid experiments
Noble liquid detectors detect the flash of scintillation light produced by a particle collision in liquid xenon or argon.
DEAP, Ontario, Canada
XENON, Gran Sasso, Italy
Indirect detection methods
Indirect detection experiments search for the products of WIMP annihilation. If WIMPs are Majorana particles (the particle and antiparticle are the same) then two WIMPs colliding could annihilate to produce gamma rays or particle-antiparticle pairs. This could produce a significant number of gamma rays, antiprotons or positrons in the galactic halo. The detection of such a signal is not conclusive evidence for dark matter, as the production of gamma rays from other sources are not fully understood.
EGRET - Energetic Gamma Ray Experiment Telescope
PAMELA - Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics
GLAST - Gamma-ray Large Area Space Telescope (also known as Fermi)