Dark Matter
Dark Matter Dark Energy There is a lot of matter in the Universe that we can’t see Dark Energy The name given to the energy causing the Universe to expand, whatever it may be Einstein called it the “Cosmological Constant”
Dark Matter in Spiral Galaxies Construct rotation curves for other galaxies using HI clouds External galaxies also show flat curves Mass-to-light ratios show that dark matter is 10x more abundant the luminous matter
Dark Matter in Elliptical Galaxies Rotation curves not possible in ellipticals No HI gas No disk Look at width of absorption lines Due to superposition of different doppler shifts Velocity appears to stay the same to large radii, similar to flat rotation curve in spirals
Dark Matter in Galaxy Clusters Evidence for dark matter from: Orbits of galaxies Hot intracluster gas temperatures Gravitation lensing
Orbits Mass determined from orbital motions Mass determined from luminosity Two masses are very different MOrbit > 10Mlum Dark matter must outweight normal matter by at least 10x
Intracluster Gas Temperature of gas tells us the total mass of the galaxy cluster Gas is in gravitational equilibrium Strength of gravity requires T~107 K Emits X-rays Mcluster >> Mgas
Gravitational Lensing Gravitational well due to mass of cluster bends light passing near cluster The more mass in the cluster, the more the light is bent
Gravitational Lensing Gravitational well due to mass of cluster bends light passing near cluster The more mass in the cluster, the more the light is bent Not enough luminous matter to bend light as much as observed
Dark matter makes up ~90% of the Universe Current theory suggests WIMPs as candidate dark matter particles MaCHOs no longer really accepted
Large Scale Structure of the Universe
Development of Structure Dark matter crucial to the development of structure Normal matter is not nearly abundant enough Gravity pulls dark matter into clumps
Development of Structure Over time, matter forms filaments and bigger clumps, which are the homes of galaxy clusters