(Submitted March 4, 2013)
In star formation, gases coalse by gravitational forces. As the pressure
increases the temperture reaches the point at which nuclear fusion begins
and the star is born. The outward pressure of the fusion holds balance with
gravity delaying further collapse as well the solar forces remaining away
from the vicinity of the star. My question is how can very massive stars
form since the gravitational force seems to cause fusion of hydrogen into
helium thus preventing further coalseing of gases?
It's a good question --- the answer lies in the finer details of the timeline
of star formation.
Nuclear fusion starts very late in the process of star formation. This
is because the high temperature and high pressure required for nuclear
fusion can be achieved only after the star has already formed. The mass
of the proto-star cloud is determined much earlier in the process. When
fusion starts, it does indeed stop any further growth of the protostar.
You can read a college undergraduate level summary at:
Hope this helps,
Koji & Alexandre
for "Ask an Astrophysicist"