Canterbury 04/11/23

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

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

Canterbury 04/11/23

The Physics of

Star Formation

Dr Dirk Froebrich

University of Kent

Canterbury 04/11/23

- How do we know stars are forming?

- Where do stars form?

- Properties of young stars

- Temperature & Turbulence vs. Gravity

- Collapse, Discs and Jets

Content

Canterbury 04/11/23

- How do we know stars are forming?

- Where do stars form?

- Properties of young stars

- Temperature & Turbulence vs. Gravity

- Collapse, Discs and Jets

Content

Canterbury 04/11/23

Inside Stars...

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

Canterbury 04/11/23

The Sky

Gal. CenterGal. Plane Gal. Plane

Gal. North Pole

Gal. South Pole

Canterbury 04/11/23

Massive O-Stars

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Massive OB-Stars

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OB-Stars + Dust

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OB-Stars + Dust

Gal. CenterGal. Plane Gal. Plane

Gal. North Pole

Gal. South Pole

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The Circinus Cloud

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B68

Canterbury 04/11/23

- 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

Content

Canterbury 04/11/23

- Where do stars form?

- in or near Giant Molecular Cloudsmostly molecular hydrogen + 1% dust+ traces of CO, H2O, NH3, ...

- these clouds are massive (104-106MSUN)

- these clouds are cold (10-30K)

Content

Canterbury 04/11/23

- How do we know stars are forming?

- Where do stars form?

- Properties of young stars

- Temperature & Turbulence vs. Gravity

- Collapse, Discs and Jets

Content

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Region S106:150 young starsforming in Cygnus

Subaru Observatory

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Region NGC346:young stars forming in the LMC

Hubble SpaceTelescope

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Tarantula Nebula:young stars forming in the LMC

Hubble SpaceTelescope

Canterbury 04/11/23

SubaruTelescope

Orion Nebula

Canterbury 04/11/23

- 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

Content

Canterbury 04/11/23

- How do we know stars are forming?

- Where do stars form?

- Properties of young stars

- Temperature & Turbulence vs. Gravity

- Collapse, Discs and Jets

Content

Canterbury 04/11/23

OriB

OriA

Ori

Betelgeuse

ONC

NGC2024

NGC2071

MON R2

The Problem:

10s of light years

Canterbury 04/11/23

The Problem:

OriB

OriA

Ori

Betelgeuse

ONC

NGC2024

NGC2071

MON R2

10s of light years Solar Diameter

Size: 1016m 109m7 orders of magnitude (x 10.000.000)

Density: changes by 21 orders of magnitude

(x 1.000.000.000.000.000.000.000)

Canterbury 04/11/23

The Problem:

OriB

OriA

Ori

Betelgeuse

ONC

NGC2024

NGC2071

MON R2

10s of light years Solar Diameter

Gravity

But why has not everything collapsed?

Thermal Pressure of gas clouds

critical (Jeans) mass for collapseabout 1MSUN for a cloud of 1ly radius

Canterbury 04/11/23

The Problem:

OriB

OriA

Ori

Betelgeuse

ONC

NGC2024

NGC2071

MON R2

10s of light years Solar Diameter

Gravity

Gravity vs. Thermal pressure

Almost all clouds are above Jeans limit should collapse But we do not observe this!

Solution: Turbulence

Canterbury 04/11/23

The Problem:

OriB

OriA

Ori

Betelgeuse

ONC

NGC2024

NGC2071

MON R2

10s of light years Solar Diameter

Gravity

Turbulence:random bulk motion of materialat supersonic velocities

v>sound speed (200m/s)

creation of shocksincreasing density

Canterbury 04/11/23

The Problem:

OriB

OriA

Ori

Betelgeuse

ONC

NGC2024

NGC2071

MON R2

10s of light years Solar Diameter

Gravity

Gravity vs. Thermal pressure + Turbulence

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

Gravoturbulent Fragmentation

Canterbury 04/11/23

- How do we know stars are forming?

- Where do stars form?

- Properties of young stars

- Temperature & Turbulence vs. Gravity

- Collapse, Discs and Jets

Content

Canterbury 04/11/23

Stage 1 Stage 2 Stage 3

Now, how does it work?

Canterbury 04/11/23

Now, how does it work?

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Orion Nebula: Discs seen in silhouette

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HH 46/47

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HH 212

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HH 46/47

HST 1994 - 1997

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HH 46/47

HST 1994 - 1997

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HH 34

HST 1994 - 1997

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HH 34

HST 1994 - 1997

Canterbury 04/11/23

The Problem:

OriB

OriA

Ori

Betelgeuse

ONC

NGC2024

NGC2071

MON R2

10s of light years Solar Diameter

Gravity

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

Canterbury 04/11/23

Planet Formation

Canterbury 04/11/23

Canterbury 04/11/23

The end