AST 248: The Search for Life in the Universe

1. How many protons does a C¹² nucleus have, and how many neutrons? 2 protons and 2 neutrons
2. C¹⁴ is radioactive. It decays when one of its neutrons changes to a proton, an electron and an antineutrino.
   1. What nucleus is thereby created? C¹⁴ has 6 protons and 8 neutrons, so after it decays it forms N¹⁴, which has 7 protons and 7 neutrons
   2. The halflife of C¹⁴ is 5730 years. If you had a sample containing 2 million atoms of C¹⁴, how long would it be until only 500,000 atoms of C¹⁴ remained? After x halflives, a sample's original number of radioactive nuclei is reduced by a factor of 1/2^x. Thus, since 500,000/2,000,000 = 1/4, the time equal to twice the halflife has occurred, or 2 x 5730 = 11,460 years.
3. What is the single property of a star at birth that determines which kind of death it will have (if it is not in a close double star system)? Its mass
4. How do most heavy elements get introduced into the interstellar medium from which planets and people can be eventually made? Supernovae disperse heavy elements into the interstellar medium.
5. What broad class of molecules are the most complex that are found in the interstellar medium? The most complex molecules found in interstellar space are organic molecules; this suggests that formation of such molecules occurs widely throughout the universe and that organic life may be common.
6. >What is the frequency of spin-flip radiation from Hydrogen atoms? Why is this radiation important? 1420 MHz. This radiation is the most powerful emission from interstellar space. It is used to map out the shape, structure and dynamics of our galaxy. It might also serve as a beacon for interstellar communications.
7. What are the three main pieces of evidence that the universe began from, or at least passed through, a period of extremely high densities and/or temperatures, commonly called the Big Bang? Hubble's observation of the recession of galaxies; Cosmic microwave background radiation; Cosmic nucleosynthesis
8. What is the approximate age of the universe, and how can this be estimated from Hubble's Constant? About 13.5 billion years. Hubble's Law is v=Hd. Comparing to d=vt one sees that if the two relations are identical, t=1/H represents the time since all galaxies were coincident in position, i.e., this is the age of the universe. The value of Hubble's constant is about H = 70 km/s/Mpc. Therefore 1/H = (1/70) (Mpc/km) s. There are 3.1 x 10¹⁹ km per parsec. There are about 3.1 x 10⁷ s per year. Therefore 1/H = (1/70) x (3.1 x 10¹⁹) (1/3.1 x 10⁷) x (10^-9 yr/Gyr) Gyr = 1000/70 Gyr = 14.1 Gyr. This is mostly correct, however, the velocity v hasn't been constant so the estimate for t is somewhat of an overestimate.