The birth of the most massive stars

The current picture of star formation looks like this: small sections of a giant molecular cloud collapse under their own gravitational attraction (or something like that), and the collapsing gas and dust forms a star. This stops once either there is no more gas and dust or the light output of the star (luminosity) is sufficiently strong to blow away the surrounding gas and dust. Massive stars are so luminous that they stop this process before enough material can collapse to form them, a problem for models. As a result, people thought that maybe massive stars from from the merger of lower mass stars. Not so, say recent observations of a massive star forming that has a dusty disk around it and is expelling material - just as observed around single low mass stars as they form as you can read here or here or here or here or in its full detail here (subscription required. Sorry.)

So how do they form, that is still a mystery. But form directly they appear to do.