2018年USAAAO短问题第11道
来自astro-init
英文题目
11. [5 pt] When a gravitationally bound system (such as a galaxy) forms, it transitions from a just bound state ($$E_{kin} = |E_{pot}|$$) to a virialized state ($$E_{kin} = 0.5|E_{pot}|$$) and the excess binding energy has to be radiated away. Consider an idealized disk galaxy with an exactly flat rotation curve with a rotation speed of $$v_{circ} = 220 km/s$$ (you can neglect the kinetic energy in random motions). Its density profile cuts off abruptly at a radius of $$R_{max} = 50 kpc$$. Assume that it took 500 million years for this galaxy to collapse to its present state. What was its mean luminosity (in units of solar luminosity) due to the release of the binding energy during that period?
