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Western University
Astronomy 1021
Reynold Silber

3/26/2013 5:22:00 PM 3/26/2013 5:22:00 PM 3/26/2013 5:22:00 PM CHAPTER 22:  Dark matter and energy  Some galaxies have different characteristics (ie. Hot gases)  Haven’t been able to measure of observe dark matter (what is it?)  Fritz Zwicky – first one to make idea of dark matter (1930s)  Stars closer to the center of the galaxy will move faster  Elliptical galaxies have dark matter but its measured in a different way  Dark matter is found in large areas to have stronger effects in galaxy clusters  X-ray observations show that the hot gas between the clusters has enough mass to hold clusters together  Measure galazy clusters masses from velocities of member galaxies or the temperature of intraclusters  Only 10% of universe we can see, rest is hidden in darkness  Gravitational lensing – when a galaxy hides what is on each side from the other  90% of galaxies clusters are dark matter  the total mass of cluster’s stars does not tell us the mass of the cluster of galaxies  two options:  dark matter really exists; we observe the effects of its gravitational attraction  our understanding of gravity is wrong; we mistakenly infer the existence of dark matter  two types of dark matter:  ordinary dark matter, massive halo objects, dead or failed stars in halos of galaxies  extraordinary dark matter, weakly interacting particles, mysterious neutrino like particles  weakly interacting particles are “best bet” for dark matter  WIMP can be found in low earth orbit  Dark matter is key in the formation of the galaxies and clusters of galaxies since it has gravity and is abundant  Gravity of dark matter caused protogalactic clouds to contract in the early universe  Dark matter’s gravitational potential wells allowed galaxy formation  Dark matter holds galaxies and clusters together  Most of the universe is dark energy and matter  Distant white-dward supernovae can be used as standard candles  Matter in the universe should slow down the expansion  Distances measured with supernovae imply that the expansion rate of the universe is speeding up (TEXTBOOK)  In the past decade the evidence for an accelerating expansion has strengthened  Dark energy, the stuff that’s making the expansion of the universe accelerate  As universe expands, density will decrease  The Doppler effect of many galaxies we can tell the universe is expanding  Einstein’s equations of general relativity can be used to describe the whole universe  High-density – fire  Low-density – ice  Dark energy is speeding up the universes expansion
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