Thursday, November 10, 2011

The Spatial Scale of Star Formation

How big are stars relative to the clouds in which they form?  Let's examine the relative scale of star formation.  A smaller star forming cloud such as the Taurus region is about 30 parsecs across.  A typical star is more or less the same size as the sun (to an order of magnitude).  If we were to shrink the molecular cloud to the size of a human body, how big would the stars be?  To find out, we set up a proportion.  The ratio of the sun's volume (4/3 * pi * (7e10 cm)^3) to the approximate volume of the cloud (4/3 * pi * (15 pc)^3) is equal to the ratio of the value we're looking for to the volume of a human body (let's estimate it as a block of 1' by 2' by 6').  Using these numbers, we discover that, if the star forming cloud were the size of a person, the forming stars would be on the order of 10^-21 cm^3 in volume.  That would mean that the radius of the star would be comparable to the radius of a DNA helix!

Now let us evaluate the relative densities.  The Taurus complex contains roughly 3e4 solar masses of gas.  This gives the region a density on the order of 10^-22 g/cm^3.  The density of a typical star like our Sun is on the order of 1 g/cm^3.  That is a difference of 22 orders of magnitude!  In comparison, lead is only 4 orders of magnitude denser than air.

Second Authors:  Eric, Lauren

1 comment:

  1. Wow, 22 orders of magnitude!

    The mass of a hydrogen atom is about 10^-24 g, so that means a "dense" star-forming region has about 100 hydrogen atoms per cubic centimeter. By comparison, the space outside our solar system close to us has about 1 atom per centimeter cubed. That's why astronomers call star-forming regions dense.

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