Location, location, location

Wanna form planets? Stay the heck away from O stars. These are the most massive stars, ones with roughly 20 or more times the Sun's mass. The amount of energy a star generates -- and therefore how hot and bright it is -- is very sensitive to the mass. Luminosity goes as the mass^3.5, so doubling a star's mass doesn't double its brightness, it makes it go up by a factor of 2^3.5 = 11.3 or so. An O star with 50 times the Sun's mass will give off nearly one million times as much energy as the Sun! Obviously, being too close to something like that would, not to put too fine a point on it, suck. Happily, massive stars are a lot less common than stars like the Sun. And they don't live as long, making them less of a threat to other stars. But, they do form ...