Astronomy Problem Set: Understanding the Universe's Evolution and Composition - Prof. Albe, Assignments of Astronomy

Download Astronomy Problem Set: Understanding the Universe's Evolution and Composition - Prof. Albe and more Assignments Astronomy in PDF only on Docsity! PROBLEM SET #5 ASTR340 – SPRING 2008 Due Date: Tuesday 29th April 2008 Book Chapters 12 and 13 1. A hot Big Bang [30 pts.] Recall that we discussed in class the evolution of the energy density in radiation versus the energy density in matter. Today, there is much more energy density in matter than in radiation, but we concluded that in the early stages of the Universe the situation must have been the reverse. A. Can you explain why we think radiation was dominant in the early universe? (Hint: recall how the radiation and matter densities change with redshift z) B. Let’s say that the radiation density today is dominated by the Cosmic Microwave Background, which we mentioned in class corresponds to about 411 photons per cubic cm (recall that 1 m3=106 cm3). The energy of one of these photons is E=hc/λ, where h is the Planck constant (h=6.63×10-34 m2 kg s-1), c is the speed of light (c=3×108 m s-1), and λ is the wavelength of light, in meters. The typical wavelength of a CMB photon is 1.1 mm. How much energy does the CMB pack in 1 cubic meter of space? (Hint: make sure all the units are compatible before plugging in numbers) C. We showed in class (and you calculated it in the previous problem set!) that the critical density of the Universe is ~10-26 kg/m3. We discussed in class the evidence that leads us to believe that the current matter density in the Universe is about 30% of this critical density. Using Einstein’s equation for the equivalence of matter and energy, E=mc2, how much energy is stored in matter form in 1 cubic meter of space? D. Who wins at the current epoch in the Universe: matter or radiation? 2. The making of the heavy elements [20 pts.] A. Describe the three main ways in which elements heavier than Hydrogen were (or are) created, and where and why those processes took (or take) place. Please say which heavy elements are manufactured where. B. What are the 4 most abundant elements? Can you explain why?