Sternentstehung - Star FormationSommersemester 2006

Henrik Beuther & Thomas Henning

24.4 Today: Introduction & Overview1.5 Public Holiday: Tag der Arbeit8.5 ---15.5 Physical processes, heating & cooling, cloud thermal structure22.5 Physical processes, heating & cooling, cloud thermal structure (H. Linz)29.5 Basic gravitational collapse models5.6 Public Holiday: Pfingstmontag12.6 Basic gravitational collapse models19.6 Accretion disks26.6 Molecular outflow and jets3.7 Protostellar evolution, the stellar birthline10.7 Cluster formation and the Initial Mass Function17.7 Massive star formation, summary and outlook24.7 Extragalactic star formation

More Information and the current lecture files: http://www.mpia.de/homes/beuther/lecture_ss06.html beuther@mpia.de

M51: The Whirlpool Galaxy

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M51: The Whirlpool Galaxy

Andromeda

CO(2-1) Optical

Mid-Infared view of part of Galactic plane

Giant Molecular Clouds

Sizes: 20 to 100pc; Masses: 104 to 106 Msun; Temperatures: 10 to 15KSuperesonic velocity dispersion ~2-3 km/s mainly due to turbulenceMagnetic field strengths of the order 10GAverage local densities ~104cm-3; Volume-averaged densities ~102cm-3

--> highly clumped material

Sites of Star Formation

1.2 mm Dust Continuum C18O N2H+

Optical Near-InfraredMasses:Between fractions and a few 100 solar masses

Densities:Of the order 106cm-3

Orion

The Star-Forming Region W43Optical Near-

Infrared1.2mm dust cont.

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/submm)Cosmic Background T 2.7 K

max= 1.1 mm (mm)

Hertzsprung-Russel diagram

Main sequence: L=4R2bT4 Stefan-Boltzmann law

Hertzsprung-Russel diagram

Free-fall time scale: tff = (3/32G)1/2 ------> tff ~ 105 yr

Contraction of protostar under gravity releasing energy as radiation: Virial theorem: Epot + 2Ekin = 0 --> Ekin = 0.5Epot = GM2/R

---> Kelvin-Helmhotz time scale: tKH = Ekin/L = GM2/RL ~ 107 yr for the sun

=105cm-3

Properties of Main Sequence Stars

Mass Sp. Type Lum Teff tMS

[Msun] [log(Lsun)] [log(K)] [yr]

60 O5 5.90 4.65 3.4x106

61 O6 5.62 4.61 4.3x106

62 O9 4.99 4.52 8.1x106

63 B2 3.76 4.34 2.6x107

64 B8 2.26 4.08 1.6x108

2 A5 1.15 3.91 1.1x109

1 G2 0.04 3.77 1.0x1010

0.8 K0 -0.55 3.66 2.5x1010

0.2 M5 -2.05 3.52 >1011} greaterthan age ofuniverse

tMS ~ 5x10-4 Mc2/L = 1x1010 (M[Msun])/(L[Lsun]) yr

Number of Stellar Types in the Milky Way

0% 1% 0% 0% 1% 3%7%

13%

68%

9%

0%

20%

40%

60%

80%

O-M F-M O B A F G K M B-F

Supergiant(I & II)

Red Giant(III)

Main Sequence (V) WhiteDwarf

Number

Sun

The easiest to seein night sky anddistant galaxies

The Milky Way

0

25

50

75

100

O-M F-M O B A F G K M B-F

Supergiant(I & II)

Red Giant(III)

Main Sequence (V) WhiteDwarf

Luminosity Class and Spectral Type

Percentage of Galactic LuminosityPercentage in Number Percentage of Galactic Stellar Mass

The cosmic cycle

Properties of Molecular Clouds

Type 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 30Dense low-mass cores 104 0.1 10 10Dense high-mass cores >105 0.1-1 10-30 100-1000

Molecules in Space

2 3 4 5 6 7 8 9 10 11 12 13 atoms--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------H2 C3 c-C3H C5 C5H C6H CH3C3N CH3C4H CH3C5N? HC9N CH3OC2H5 HC11NAlF C2H l-C3H C4H l-H2C4 CH2CHCN HCOOCH3 CH3CH2CN (CH3)2CO AlCl C2O C3N C4Si C2H4 CH3C2H CH3COOH? (CH3)2O NH2CH2COOH? C2 C2S C3O l-C3H2 CH3CN HC5N C7H CH3CH2OH CH3CH2CHO CH CH2 C3S c-C3H2 CH3NC HCOCH3 H2C6 HC7N CH+ HCN C2H2 CH2CN CH3OH NH2CH3 CH2OHCHO C8H CN HCO CH2D+? CH4 CH3SH c-C2H4O CH2CHCHO CO HCO+ HCCN HC3N HC3NH+ CH2CHOH CO+ HCS+ HCNH+ HC2NC HC2CHO CP HOC+ HNCO HCOOH NH2CHO CSi H2O HNCS H2CHN C5N HCl H2S HOCO+ H2C2O HC4N KCl HNC H2CO H2NCN NH HNO H2CN HNC3 NO MgCN H2CS SiH4 NS MgNC H3O+ H2COH+ NaCl N2H+ NH3 OH N2O SiC3 PN NaCN C4 SO OCS SO+ SO2 SiN c-SiC2 SiO CO2 SiS NH2 CS H3+ HF SiCN SH AlNC FeO(?) SiNC

Currently 129 detected interstellar molecules (from November 2005)

The Interstellar Medium I

Atomic Hydrogen

Lyman at 1216 A

o

The 21cm line arises when the electron spin S flips from parallel(F=1) to antiparallel (F=0) compared to the Proton spin I.

E = 5.9x10-5 eV

The Interstellar Medium II

Molecular Hydrogen

Carbon monoxide CO Formaldehyde H2CO Cyanoacetyline HC3N

Excitation mechanisms:- Rotation --> usually cm and (sub)mm wavelengths- Vibration --> usually submm to FIR wavelengths- Electronic transitions --> usually MIR to optical wavelengths

The Interstellar Medium IIIIonized gas

- H2 recombination lines from optical to cm wavelengths- Emission lines from heavier elements --> derive atomic abundances He/H 0.1 C/H 3.4x10-4

N/H 6.8x10-5

O/H 3.8x10-4

Si/H 3.0x10-6

- Free-free emission between e- and H+

cm mm submm

Interstellar dust: Extinction

Extinction dims and reddens the light

Dust composition:Graphite CSilicon carbide SiCEnstatite (Fe,Mg)SiO3

Olivine (Fe,Mg)2SiO4

Iron FeMagnetite Fe3O4

Size distribution:Between 0.005 and 1mn(a) ~ a-3.5 (a: size)

(Mathis, Rumpl, Nordsieck 1977)

Optical Near-Infrared

Interstellar dust: Thermal emissionS() = N (/D2) Q() B(

With N dust grains of cross section at a distance D, a dust emissivityQ~2 and the Planck function B(,T). In the Rayleigh-Jeans limit, we have

S() ~ 4

The thermal dust emission isoptically thin and hence directly proportional to the dust columndensity. With a dust to gas massratio of ~1/100, we can derivethe gas masses.

Colour: MIRContours: mm continuum

Dust polarization and magnetic fields

BPol. E

Dust

Molecular filaments can collapse along their magnetic field lines.

Polarized submm continuum emission

Star Formation Paradigm

Sternentstehung - Star FormationSommersemester 2006

Henrik Beuther & Thomas Henning24.4 Today: Introduction & Overview1.5 Public Holiday: Tag der Arbeit8.5 ---15.5 Physical processes, heating & cooling, cloud thermal structure22.5 Physical processes, heating & cooling, cloud thermal structure (H. Linz)29.5 Basic gravitational collapse models5.6 Public Holiday: Pfingstmontag12.6 Basic gravitational collapse models19.6 Accretion disks26.6 Molecular outflow and jets3.7 Protostellar evolution, the stellar birthline10.7 Cluster formation and the Initial Mass Function17.7 Massive star formation, summary and outlook24.7 Extragalactic star formation

More Information and the current lecture files: http://www.mpia.de/homes/beuther/lecture_ss06.htmlbeuther@mpia.de