Download Galactic Rotation and Dark Matter Powerpoint

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
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
Gravitational Lensing
Abell 1689
LRG-3757
The Bullet Cluster
More evidence for dark matter
Velocity dispersion of galaxies
Measurements of the velocities of galaxies within clusters.
Acoustic oscillations
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
Structure formation
If the Big Bang model is correct, dark matter is required to
allow structures to form.
Rotation curves
A solid body (i.e. a disk) will
have a rotational velocity
that is proportional to
distance – as R increases, v
increases.
𝑚𝑣 2
𝑟
𝐺𝑀𝑚
Since
= 𝑟 2 , for objects
that are gravitationally
bound (i.e. not a solid disk),
we expect v to be
1
proportional to 2
𝑅
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
𝑣 ≈ constant
𝑣∝
𝑣∝𝑅
1
𝑅
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.
XENON, Gran Sasso, Italy
DEAP, Ontario, Canada
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)