Forming Stars: W51A - A Case Study

Ever since I was introduced to a Creationist claiming it's impossible to form new stars, I've been extra interested in journal articles that highlight how well our theory of stellar formation and evolution lines up with the evidence. It's been a pretty hot topic on this blog and a new ApJ article adds yet another confirmation that we're not just making things up when it comes to our knowledge of stars.

The article looks at a star forming region called W51A that is a bubble in the gaseous cloud in which it resides. In the paper, it addresses two major points of the formation of stars:

1) The required density for stellar condensation
2) The ability of expanding shells driven by other stars to cause the necessary overdensities

In order to analyze the first point, the researchers used a correlation between the amount of CO molecules (which can be determined via spectroscopy) and hydrogen to find the location the hydrogen is the densest. As expected, several locally dense regions exist near the perimeter of the bubble. Based on their estimations, they found the density to already be greater than the theoretical density necessary for the cloud to start fragmenting into stars. Given we see young stars in regions predicted by theory, that suggests that we're doing pretty well on the first point.

For the second, the group needed to tie the formation of the bubble to a star within it. By measuring the radial velocity of the bubble near the edges, the team could trace back how long it should have taken for the bubble to grow to its current diameter as well as determining the approximate center. Near that center, they find a massive star (which they estimate to be a O8.5 main sequence star) which would likely be the reason for the bubble. But to really test the feasibility for this star to make the bubble, they match these observations with theoretical calculations for similar regions from a 2006 paper. The predictions from the model predict a time scale and shell size that line up excellently.

So from this, two points of stellar formation are, yet again, supported by observational evidence.

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Kang, M., Bieging, J., Kulesa, C., & Lee, Y. (2009). TRIGGERED STAR FORMATION IN A DOUBLE SHELL NEAR W51A The Astrophysical Journal, 701 (1), 454-463 DOI: 10.1088/0004-637X/701/1/454