How do some stars get so massive?

One of the most massive and brightest stars in the Milky Way, Eta Carinae is a hypergiant star, dominating this frame taken by the combined efforts of NASA’s Spitzer Space Telescope and the Digital Sky Survey

Some stars are the same size as our Sun, others are smaller, but there are some that defy all expectations. These stars are monstrously sized, with some weighing in at up to around 120-times the mass of our star.

We know that the majority of stars begin their lives in a nursery of gas and dust, located in a galaxy. When these gigantic birthing sites, or clouds, collapse, a star is born. This is also true for stars hitting around 20-times our Sun’s heft, which are able to suck in the matter that surrounds them. However, as they get heavier and heavier, astronomers have been at a loss as to how they form at all.

A collapsing star of 20 solar masses or less is able to pull in a swirling accretion disk around it but anything more than this and a star will prefer to blow out radiation to such an extent it makes grabbing hold of the material to make its massive size incredibly difficult. In essence, these stars are starving themselves of the sustenance they need to continue growing. Astrophysicists are trying to put together plausible models, but there are still gaps in our knowledge when it comes to how these huge stars ever come into existence.

Observations have shown that extremely massive stars do form like stars of 20 solar masses or less, with accretion disks and matter streaming onto them in spite of their powerful radiation. One of several theories put forward is that older stars close by corral the surrounding gas with their own radiation, forcing it onto the forming giant. Another possibility is that magnetic fields in the collapsing gas cloud may be able to hold a cloud of potentially star-forming gas together until it grows so massive that it can
do nothing else but collapse under its own gravity to form a monstrous star.

Image Credit: NASA