Star Formation in our Galaxy
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Transcript of Star Formation in our Galaxy
Star Formation in our Galaxy
Dr Andrew Walsh (James Cook University, Australia)
Lecture 1 – Introduction to Star Formation Throughout the Galaxy
Lecture 2 – Chemistry and Star Formation
Lecture 3 – High Mass Star Formation and Masers
Lecture 4 – G305.2+0.2: A Case Study and Galactic Plane Surveys
Star Formation in our Galaxy
Introduction to Star FormationThroughout the Galaxy
1.Why study star formation?2.The Galactic ecology3.Dark clouds, complexes and giant molecular clouds4.The Milky Way at different wavelengths5.Young stellar object classes6.Disks, jets and outflows7.Gravitational collapse8.Clustered star formation
Why Study Star Formation?
Star formation is the process that determines the properties of the major
building blocks of the universe:
Stars, Planets and Galaxies
Why Study Star Formation?
The birth of stars is the most poorly understood stage of evolution of stars
Star formation is one of the most beautiful processes in the cosmos!
McCaughrean et al. 1996
The Galactic Ecology
Supernova
Molecular Cloud
Cores
Young stellar objects
Stars
High mass
Low mass
Planetary nebula
White dwarf
Neutron star
Black hole
TriggeringSN shocks
HMS w
inds
Outflow
s
Cores, Dark clouds, Complexes andGiant Molecular Clouds
Giant Molecular Clouds:~105 solar masses~50pc
Cores, Dark clouds, Complexes andGiant Molecular Clouds
Dark Cloud Complexes:~104 solar masses~10pc
Cores, Dark clouds, Complexes andGiant Molecular Clouds
NH3 (1,1)
Dark Clouds
Dark CloudsOptical Near-InfraredMasses:
Between fractions and a few x 10 solar masses
Sizes:~1pc
Interstellar Extinction
Red light is absorbed by dust less than blue light
We can see deeper into dust-enshrouded objects at longer wavelengths.
Extinction ~ λ-1.7
Dark Clouds
1.2 mm Dust Continuum C18O N2H+
Optical Near-InfraredMasses:Between fractions and a few x 10 solar masses
Sizes:~1pc
Properties of Cores, Dark clouds, Complexes and Giant Molecular
CloudsType n Size T Mass [cm-3] [pc] [K] [Msun]
Giant Molecular Cloud 102 50 15 105
Dark Cloud Complex 5x102 10 10 104
Individual Dark Cloud 103 2 10 30
Dense low-mass cores 104 0.1 10 10
Dense high-mass cores >105 0.1-1 10-30 100-1000
Planck's Black Body
Planck's Black Body
Wien's Law
max
= 2.9/T [mm]
Examples:
The Sun T 6000 K max
= 480 nm (optical)Humans T 310 K
max= 9.4 m (MIR)
Molecular Clouds T 20 K max
= 145 m (FIR)Cosmic Background T 2.7 K
max= 1.1 mm (mm)
Spectral Energy Distribution
Class 0, I, II and III Young Stellar Objects
McCaughrean et al. 1996
Discovery of outflowsHerbig 1950, 1951; Haro 1952, 1953
Initially thought to be embedded protostars but soon spectra were recognized as caused by shock waves --> jets and outflows
Discovery of outflows
- In the mid to late 70th, first CO non-Gaussian line wing emission detected (Kwan & Scovile 1976).- Bipolar structures, extremely energetic, often associated with HH objects
Bachiller et al. 1990Snell et al. 1980
The prototypical molecular outflow HH211
General outflow properties
- Jet velocities 100-500 km/s <==> Outflow velocities 10-50 km/s- Estimated dynamical ages between 103 and 105 years- Size between 0.1 and 1 pc- Force provided by stellar radiation too low (middle panel) --> non-radiative processes necessary!
Mass vs. L Force vs. L Outflow rate vs. L
Wu et al. 2004, 2005
Snell et al. 1980
Spectral Line Profiles• Outflow wings
• Infall
1. Rising Tex along line of sight2. Velocity gradient3. Line optically thick4. An additional optically thin line peaks at center
Spectral Line Profiles• Outflow wings
• Infall
Infall ProfilesHCO+ (1-0) Optically thick
N2H+ (1-0)Optically thin
Walsh et al. 2006
Infall Profiles
Walsh et al. 2006
Clustered Star Formation
Clustered Star Formation
Most stars are formed in clusters
(Maybe) ALL High Mass StarsFormed in Clusters
Spitzer 3-colour image of NGC 1333 - Courtesy Rob Gutermuth (CfA)Spitzer 3-colour image of NGC 1333 - Courtesy Rob Gutermuth (CfA)
Spitzer 3-colour image of NGC 1333 - Courtesy Rob Gutermuth (CfA)Spitzer 3-colour image of NGC 1333 - Courtesy Rob Gutermuth (CfA)
Spitzer 3-colour image of NGC 1333 - Courtesy Rob Gutermuth (CfA)Spitzer 3-colour image of NGC 1333 - Courtesy Rob Gutermuth (CfA)
Clustered Star Formation
Walsh et al. 2007
Red & Blue = HCO+ (1-0)
Greyscale = N2H+ (1-0)
+ = dust continuum cores
Clustered Star Formation