Cosmological Mysteries

Some notes from a lecture on Dark Matter and Structure formation in the Universe (Part 1 of 3):

  • Zone of avoidance: the region along the galactic equator that cannot be easily observed due to the absorption of light from the dust in the plane of the Milky Way
  • Universe expansion does not play in local effect such as star – planet, star – star, and even local galaxy – galaxy. “Close in” galaxies (such as ours and Andromeda) are actually approaching (display blue shifts). Once the 1 / r^2 of gravity falls off the expansion (red shift) effects are seen.
  • Sloan Digital Sky Survey (SDSS) is an effort to map one million galaxies in the universe. The process is done via measuring red shifts.
    Stars can be separated from galaxies by looking for a 4 spike cross. Stars are essentially points that cannot be resolved which causes a star pattern from the lenses. Galaxies will appear as blobs as they can be resolved. (I need to find a definitive reference for this phenomena.)
  • NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) is measuring the cosmic background radiation.
  • By combining the results of the SDSS and WMAP physical evidence is found for the existance of dark energy. Dark energy is gravitationally repulsive. What’s interesting about dark energy is that it corresponds to Einstein’s cosmological constant. The cosmological constant was added by Einstein to his equations to achieve a static model of the universe. After it was determined that the universe was not static (it’s currently expanding) this constant was considered to be Einstein’s blunder. It seems that Einstein was right after all.
  • Dark matter does not lose energy like standard matter does. Standard matter (baryons) loses energy (by radition) and will condense forming dense matter. Dark matter on the other hand does not lose energy and therefore has a lower bound on its density. Because of this dark matter does not have an effect on the planetary scale as standard matter dominates. As the scale moves to intergalactic distances the density of dark matter is such that it contributes to interactions.
  • “Gravity is like the economy: the rich get richer and the poor get poorer.” The results of gravity follow that of chaos — that is, it is highly dependent on initial conditions. Small initial anisotropies in a distribution of matter will quickly become large clusters of matter. A locally dense region will pull more and more matter into it (“the rich get richer”) and a locally spare region will have more and more matter pulled from it (“the poor get poorer”).
  • Using the background microwave radiation (from WMAP) as a baseline, simulations have been performed to show that fibers similar to that seen in the results of SDSS evolve.
    It has also been shown that the effects of dark matter / energy must be added into these simulations in order to maintain the structure of the filaments. The dark matter / energy dominates over the gravitional effects to curtail further collapse of the filaments

Course slides are available.
A useful astronmy reference.
Thank you Andrey Kravtsov for a great talk!


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