1. The Formation of Stars
Where do they come from?
How do they form?

2. Star Formation
Last week…stellar evolution. What happens after the main sequence. (Will return to shortly)
Now, how to stars form? What do they form from? Space seems to be empty. Where does the material come from?

3. Space isn’t really empty
Stars move in a dilute “atmosphere” called the interstellar medium.
Typical density of atoms/cc
Compare with density of 4E+19 atoms/cc in the Earth’s atmosphere
Compare with 1024 atoms/cc mean density for Sun.

4. Putting together the pieces in the puzzle
To see how stars form, look at places where there are young stars.
When we see massive main sequence stars (spectral class O), we know they are young.
With fairly simple observations, we can find groups of O and B stars (OB associations)

5. Young star clusters (the Rosette Nebula and Chi & h Persei)

6. The primary example: The Orion Nebula

7. Fact that stars form in star clusters means the Sun has siblings out there

8. Stars form in the presence of dark clouds

9. Dark clouds due to particulate matter
Small particle absorb and scatter light
Demo
Particles primarily formed of carbon, silicates
Most of matter which forms stars must be elsewhere

10. Where the gas is: molecular and very cold
Discovery was a contribution of radio astronomy
Utilized observations of rotational transitions of molecules
Emission from molecules
Like CO, water, ammonia
Made with radio telescopes

11. The sky in the glow of the carbon monoxide molecule

12. How do stars form from these molecular clouds?

13. A Star is born….

14. A Star is born (Part 2) …

15. What a new star (protostar) looks like
What a new star (protostar) looks like. We can study nearby examples in Taurus

16. Molecular Clouds as Chemistry Sets in the Sky
Number of molecules discovered in molecular clouds = 152
8 species with 10 or more atoms
Deuterated species overrepresented

17. The future of molecular cloud studies…ALMA
64 antenna interferometer
2010 August, “first science”
2012 December, “full science operations”

18. ALMA