The Formation of Stars

(This is the write up of worksheet 10) 

1. The spatial scale of star formation: 
• If you let the size of your body represent the size of the star forming complex, how big would the forming stars be?  Let's consider a star forming region (like the Taurus region) that is about 30pc. 1 parsec is roughly 206264 AU, and 1 AU is roughly 100 solar diameters. If we consider the size of a typical star to be roughly that of the sun, a star is 1/30*20626400 in size of the star forming complex. Now let's compare this estimate to the human body. Say the average human body is 1.5 meters; then 1.5/618792000 is roughly 2.42*10^-9 meters. That's on the order of a tenth of the size of a cell membrane! That sure puts things into perspective! 

• The average density of a typical star (using our sun as a model) is:  If the Taurus complex contains roughly 3*10^4 solar masses in a radius of 15 parsecs, then the average density of the region is 3.0*10^-23 times less than that of a typical star, which is roughly 1.4*10^-23 g/cm^3. 

3. Proto-stars and the pre-main sequence

• The rate at which mass accumulates onto a forming star is                                                                                                                        rearranging these equations, we find that                                                                        
• To find the time it would take to build up stars of a certain mass (1 solar mass and 30 solar masses in this problem), we integrate the accretion rate with respect to time.                                                                                                                                                        using cgs units where G=6.8*10^-8 cm^3/g/s^2, Msun = 2*10^33 g, and the speed of sound = 2.5*10^4cm/s , we find that it takes 8.7*10^12 seconds to build up a 1 solar mass star and 2.6*10^14 seconds to build up a 30 solar-mass star. In more familiar units, it takes roughly 2.8*10^5 years to build up a 1 solar-mass star and 8.3*10^6 years to build up a 30 solar mass star. 
• The Kelvin-Helmholtz time scale is given by                                 
  In this problem, we are dealing with a 1 solar mass star (L ~ 100 solar luminosities) and a 30 solar mass star (L ~ 10^5 solar luminosities). Using the above equations and the fact that mass scales roughly as radius, we find that the Kelvin-Helmholtz time scale for the 1 solar mass star is 5.8*10^12 seconds ~ 1.8*10^5 years and the time scale for the 30 solar mass star is 1.7*10^11 seconds ~ 5.5*10^4 years. These numbers are an order of magnitude smaller than the accretion time scales. 
• The results from the previous part suggest that larger stars reach their main sequence faster than smaller stars. In general, larger stars have much shorter life-spans than smaller stars. 

I would like to thank Juliette and Tommy for working with me! 

A Starry Sky for my Room

I've been pretty busy lately, so I haven't had the chance to do very many posts. I was planning on getting to my blog earlier today, but I got side tracked. My friend and I decided to make a quick Target run. While she was looking for drawers, I came across some wall stickers. Browsing around, I found glow-in-the dark star shaped stickers!!! Needless to say, I spent the evening sticking them up on my wall. Funny enough, I had to use my Astro text book to help me reach the high spots (it's the thickest text book I own :P ).  

Unfortunately, I can't find a camera that has the ability to take a photo of these in the dark - but the stars look a million times better when they glow.  

Professional Astronomer

I've been trying to think about what it takes to be a professional astronomer since the writing assignment was posted. In general, I'm still very confused about the fine line between astronomy and astrophysics. Traditionally, astronomy is associated with observation and astrophysics is more associated with physics. However, in recent years as our knowledge of the field has greatly increased, that distinction has grown fainter and fainter. I talked to Melody about her thoughts on the subject and she explained that the difference lies in the approach. Astronomers observe the universe and use what they find to find out more about the universe. Astrophysicists use a physics approach to predict behavior of astrophysical objects.


In general, I feel like the term "Astronomer" is more like an umbrella that encompasses a lot of different types of professions and skills that ultimately serve to further our knowledge of the cosmos. For example, last summer I did an Astrophysics SURF, but most of what I did was technically computer science. However, the results contribute to the understanding of stellar objects, so it's considered as Astrophysics. 


Now that I've officially put in some thought in to this, I feel like I'm more confused than I was when I started.  I used to think that an Astronomer was someone who just did observing and an Astrophysicist was someone who did all the physics-y calculations.  Now I see that the line between the two professions isn't as clear. So far, I consider myself an astrophysicist. I'm curious to see if that will change by the end of this assignment.