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The problem of star formation is not how to make stars. The problem of star formation is how not to make stars. The Physics of Star Formation. Dr Dirk Froebrich University of Kent. Content. - How do we know stars are forming? - Where do stars form? - Properties of young stars

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Presentation Transcript
slide1

The problem of star formation is not how to make stars.

The problem of star formation is how not to make stars.

slide2

The Physics of

Star Formation

Dr Dirk Froebrich

University of Kent

slide3

Content

- How do we know stars are forming?

- Where do stars form?

- Properties of young stars

- Temperature & Turbulence vs. Gravity

- Collapse, Discs and Jets

slide4

Content

- How do we know stars are forming?

- Where do stars form?

- Properties of young stars

- Temperature & Turbulence vs. Gravity

- Collapse, Discs and Jets

slide5

Inside Stars...

Massive stars are bright and short lived (few Million years)

slide6

The Sky

Gal. North Pole

Gal. Plane

Gal. Center

Gal. Plane

Gal. South Pole

slide10

OB-Stars + Dust

Gal. North Pole

Gal. Plane

Gal. Center

Gal. Plane

Gal. South Pole

slide12

B68

k  lb

slide13

Content

- How do we know stars are forming?

- short lived massive stars exist

- they must have formed in the last few Myrs

- the Universe is 13.7Gyrs old

slide14

Content

- Where do stars form?

- in or near Giant Molecular Clouds

mostly molecular hydrogen + 1% dust

+ traces of CO, H2O, NH3, ...

- these clouds are massive (104-106MSUN)

- these clouds are cold (10-30K)

slide15

Content

- How do we know stars are forming?

- Where do stars form?

- Properties of young stars

- Temperature & Turbulence vs. Gravity

- Collapse, Discs and Jets

slide16

Region S106:

150 young stars

forming in Cygnus

Subaru Observatory

slide17

Hubble Space

Telescope

Region NGC346:

young stars forming

in the LMC

slide18

Hubble Space

Telescope

Tarantula Nebula:

young stars forming

in the LMC

slide19

Orion Nebula

Subaru

Telescope

slide20

Content

- Properties of young stars

- they are ‘social‘ – most form in clusters,

some in isolation

- single/binary/tripple/multiple – 147/64/9/1

- many low mass and few high mass stars,

universal mass distribution

slide21

Content

- How do we know stars are forming?

- Where do stars form?

- Properties of young stars

- Temperature & Turbulence vs. Gravity

- Collapse, Discs and Jets

slide22

The Problem:

Betelgeuse

MON R2

l-Ori

NGC2071

OriA

NGC2024

ONC

10s of light years

OriB

slide23

Betelgeuse

MON R2

l-Ori

NGC2071

OriA

NGC2024

ONC

10s of light years

OriB

The Problem:

Solar Diameter

Size: 1016m  109m

7 orders of magnitude (x 10.000.000)

Density: changes by 21 orders of magnitude

(x 1.000.000.000.000.000.000.000)

slide24

Betelgeuse

MON R2

l-Ori

NGC2071

OriA

NGC2024

ONC

10s of light years

OriB

The Problem:

Gravity

Solar Diameter

But why has not everything collapsed?

Thermal Pressure of gas clouds

 critical (Jeans) mass for collapse

about 1MSUN for a cloud of 1ly radius

slide25

Betelgeuse

MON R2

l-Ori

NGC2071

OriA

NGC2024

ONC

10s of light years

OriB

The Problem:

Gravity

Solar Diameter

Gravity vs. Thermal pressure

Almost all clouds are above Jeans limit

 should collapse

 But we do not observe this!

Solution: Turbulence

slide26

Betelgeuse

MON R2

l-Ori

NGC2071

OriA

NGC2024

ONC

10s of light years

OriB

The Problem:

Gravity

Solar Diameter

Turbulence:

random bulk motion of material

at supersonic velocities

v>sound speed (200m/s)

creation of shocks

increasing density

slide27

Betelgeuse

MON R2

l-Ori

NGC2071

OriA

NGC2024

ONC

10s of light years

OriB

The Problem:

Gravity

Solar Diameter

Gravity vs. Thermal pressure + Turbulence

Star Formation is the interplay of Gravity and supersonic turbulence in Molecular Clouds

 Gravoturbulent Fragmentation

slide28

Content

- How do we know stars are forming?

- Where do stars form?

- Properties of young stars

- Temperature & Turbulence vs. Gravity

- Collapse, Discs and Jets

slide29

Stage 1

Stage 2

Stage 3

Now, how does it work?

slide36

HH 46/47

HST 1994 - 1997

slide37

HH 46/47

HST 1994 - 1997

slide38

HH 34

HST 1994 - 1997

slide39

HH 34

HST 1994 - 1997

slide40

Betelgeuse

MON R2

l-Ori

NGC2071

OriA

NGC2024

ONC

10s of light years

OriB

The Problem:

Gravity

Solar Diameter

Gravity vs. Thermal Pressure + Turbulence

+ angular Momentum + magn. Fields

Spin  accretion disc formation  ejection of jets (accelerated and collimated by magnetic fields)

 feedback from outflows and radiation  turblence