Download 22 October: The Formation of Stars

The Formation of Stars
Where do they come from?
How do they form?
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?
Space isn’t really
empty
• Stars move in a dilute
“atmosphere” called the
interstellar medium.
• Typical density of 10100 atoms/cc
• Compare with density of
4E+19 atoms/cc in the
Earth’s atmosphere
• Compare with 1024
atoms/cc mean density
for Sun.
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)
Young star clusters (the Rosette Nebula
and Chi & h Persei)
The primary example: The Orion
Nebula
Fact that stars form in star clusters means
the Sun has siblings out there
Stars form in the presence of dark
clouds
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
Where the gas is: molecular and very cold
• Discovery was a
Emission from
contribution of
molecules
radio
Like
CO,astronomy
water,
•ammonia
Utilized
Made
with radio of
observations
telescopes
rotational
transitions of
molecules
The sky in the glow of the carbon
monoxide molecule
How do stars form from these
molecular clouds?
A Star is born….
A Star is born (Part 2) …
What a new star (protostar) looks like. We
can study nearby examples in Taurus
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
The future of molecular cloud
studies…ALMA
• 64 antenna interferometer
• 2010 August, “first science”
• 2012 December, “full science operations”
ALMA