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The Question

(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?

The Answer

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"

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