Lectures 11-13 ยท Student-facing assignment
Show reasoning, units, diagrams or plots where useful, and source acknowledgments. Numerical answers without explanation receive limited credit. Eligible submissions may be revised after feedback.
A star at radius r = 8 kpc orbits at 220 km/s. Another star at r = 16 kpc also orbits at about 220 km/s. Using v^2 approximately GM(r)/r, how must enclosed mass change between 8 and 16 kpc? Why is this evidence for unseen mass?
A galaxy has a smooth reddish light profile, little visible gas or dust, and no obvious spiral arms. Classify it as spiral, elliptical, or irregular, and state one piece of evidence that could complicate the classification.
A galaxy has recession speed 7000 km/s. Using H0 = 70 km/s/Mpc, estimate its distance in Mpc. Name two reasons this estimate may be imperfect.
A spectral line with rest wavelength 500.7 nm is observed at 515.7 nm. Compute redshift z and approximate recession speed for low redshift. Use c = 3.00 x 10^5 km/s.