Big Stars Need the Help From the Little Guys

We know that there are massive stars out there that can be 10 to 150 times larger than the mass of the sun. These massive stars are rare but produce most the heavy elements in the galaxy when they explode in supernovas. Astrophysicists have been looking at the condition inside cold clouds of molecular hydrogen that favor the formation of massive stars over low-mass stars like the sun. They believe that the early formation of a low mass star in a cloud paves the way for the formation for larger stellar big stars rather than the cloud breaking down into smaller clouds that would produce a bunch of low mass stars. It is when the cloud is cold that it tends to break up into smaller stars but as it gets warmer it can form larger and larger objects. When a star forms in a hydrogen cloud it has a zone of influence around it that it heats up. If it is a low density cloud the influence is small and its effect is unimportant and causes the system to break up. As the density of the cloud increases that influence of the low mass stars warms up the gas and eventually a few low mass stars have heated up the entire cloud causing it to collapse into a massive star. The density of the cloud must be roughly around a million hydrogen molecules per cubic centimeter which is roughly about 10 trillions time greater than earth's atmosphere. scientist also believe that it is possible for low mass stars to form in the outer regions of these clouds where densities are a little less. But this is hard to observe seeings that from earth we can only see the big, bright stars.

http://www.spacedaily.com/reports/Small_Helper_Stars_Needed_For_Massive_Star_Formation_999.html