Chapter 19

A protostar on the Hayashi track evolves from a temperature of \(3500 \mathrm{K}\) and a luminosity 5000 times that of the Sun to a temperature of \(5000 \mathrm{K}\) and a luminosity of 3 solar units. What is the protostar's radius (a) at the start and (b) at the end of the evolution?

What is the luminosity, in solar units, of a brown dwarf whose radius is 0.1 solar radius and whose surface temperature is \(600 \mathrm{K}(0.1 \text { times that of the } \operatorname{Sun}) ?\)