Star Formation

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0
Star Formation
2
Giant Molecular Clouds
0
Barnard 68
Infrared
Visible
Star formation ? collapse of the cores of giant
molecular clouds Dark, cold, dense clouds
obscuring the light of stars behind them.
3
Parameters of Giant Molecular Clouds
0
Size r 50 pc
Mass 106 Msun
Temp. 20 K
Density 100 300 cm-3
Hot, dense cores
r 0.05 - 1 pc
M 10 - 100 Msun
T 100 - 200 K
n 107 109 cm-3
Bok globules
r 1 pc
M 1 - 1000 Msun
T 10 K
n 104 cm-3
4
0
Trifid Nebula
Bok Globules
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Globules
0
Bok Globules
10 1000 solar masses
Contracting to form protostars
6
Globules
0
Evaporating Gaseous Globules (EGGs) Newly
forming stars exposed by the ionizing radiation
from nearby massive stars
7
Fragmentation
0

• MJ T3/2 r-1/2
• r-1/2
• during isothermal collapse
• Fragmentation
• gt Stars do not form isolated, but in large
  groups, called Open Clusters of Stars.

Open Cluster M7
8
Free Fall of a GMC Core
9
Protostars
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Protostars pre-birth state of stars
Hydrogen to Helium fusion not yet ignited
Still enshrouded in opaque cocoons of dust gt
barely visible in the optical, but bright in the
infrared.
10
Pre-Main-Sequence Evolution
0
Hydrostatic equilibrium reached
? Adiabatic collapse
? Heating
Isothermal collapse of the protostar
Gravitational energy release in equilibrium with
radiative cooling Hayashi Track
Isothermal collapse ? Formation of a protostellar
core
11
Pre-Main-Sequence Evolution
0
Star emerges from the enshrouding dust cocoon
Hayashi Track
First thermonuclear reactions p 21H ? 32He
g
Radiative core develops
p p ? 21H e ne and 126C-burning steps of
CNO cycle set in
Core expands T drops
126C supply exhausted final adjustment to ZAMS
12
Young Star Clusters
0

• Containing very young, hot O/B stars

? O/B associations
Stars fully evolved towards ZAMS
8 million years
Luminosity
Stars still contracting and evolving towards ZAMS
ZAMS
30 million years
Temperature
13
HII Regions
0
The Strömgren Sphere
rs 0.3 pc for a typical O6 star
H ionization rate recombination rate
Ngt13.6 eV (4/3) p rs3 nH2 a
a 3.1x10-13 (T/8000 K)-1/2 cm3 s-1
rs (3 Ngt13.6 eV) / (4 p nH2 a)1/3
14
Protostellar Disks and Jets Herbig Haro Objects
0
Disks of matter accreted onto the protostar
(accretion disks) often lead to the formation
of jets (directed outflows bipolar outflows)
Herbig Haro Objects
15
Protostellar Disks and Jets Herbig Haro Objects
(II)
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Herbig Haro Object HH34
16
Protostellar Disks and Jets Herbig Haro Objects
(III)
0
Herbig Haro Object HH30
17
The Orion Nebula An Active Star-Forming Region
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The Trapezium
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The 4 trapezium stars Brightest, very young
(less than 2 million years old) stars in the
central region of the Orion nebula
Only one of the trapezium stars is hot enough to
ionize hydrogen in the Orion nebula
Infrared image 50 very young, cool, low-mass
stars
X-ray image 1000 very young, hot stars
The Orion Nebula
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0
Kleinmann-Low nebula (KL) Cluster of cool, young
protostars detectable only in the infrared
The Becklin-Neugebauer Object (BN) Hot star,
just reaching the main sequence
Spectral types of the trapezium stars
B3
B1
B1
O6
Visual image of the Orion Nebula
Protostars with protoplanetary disks