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The Origin of Stars
Professor Michael D. Smith
Inaugural Lecture
University of Kent
12 November, 2009
The Origin of Stars
Professor Michael D. Smith
Lecture
University of Kent
12 November, 2009
We have problems
We now know that we don’t know……
………
what we thought we knew……
What the Universe is made of
How Galaxies form
How Stars form
Issues and debates
We are not familiar with our own Universe.
What is the mysterious dark matter and dark
energy?
What are they and why are they necessary?
What came first: galaxies, quasars or stars?
A question of evolution: top-down or bottom-up?
Was our Universe designed with us in mind?
Are there other civilisations, other Universes?
The recipe for the Universe begins………IYA2009
We need to know ……..
Why do we need to know?
Curiosity? Principles?
The most fundamental science.
Energy
Environments
Driver for emergence of totally new concepts
Driver for pioneering technology
We need to create……..
Science is more creative than Art
Stumble and then leap
Work in the dark
But all established laws must be obeyed
Teach: making creators
Aim: to express the unexpressed.
To make explicit what is implicit.
Where do stars come from?
Science. LoFAR Stamp. Impact?
The scene: what is a star?
• Ball of gas
• Photosphere; corona
• Stable phase; nuclear fusion reactors,
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gravity, radiation, convection.
come from?
Centuries: idea of swirling,
turbulent gas as the origin of
our solar system.
Descartes, Kant, Laplace:
vortices, nebular
hypothesis: importance of
angular momentum.
Decades: dark patches: black box gas, dust + magnetic field:
OBSCURED
Is there a problem with clouds?
Classical approach: Gravity works alone
• Global expansion + local collapse
• Giant clouds condense, collapse,
fragment
• Process is rapid: clouds consumed within few
hundred million years
• Yet we detect plenty of clouds: clouds exist
• Some Unknown Unknown (UU) holds up the clouds
Known means of cloud support
• Rotation: angular momentum
• Magnetic field (standard model)
• Turbulence: random supersonic motions
• Cloud evolution is delayed
• Stars can still form today
observations: answer
• Rotation: only after collapse
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Magnetic field: invisible
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Turbulence: supersonic motions: YES
• No need to introduce an Unknown Unknown
• …although we can’t follow a cloud’s evolution
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and can’t be confident of the physics and
•
dynamics.
The Trifid
a problem with young stars…..
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Young stars observed – very active, accreting
Associated (intimately) with clouds
Lifetimes: very short - few million years
Rejuvinated old stars? Von Weizsaecker – 1950s
Kent SEPnet Astrodome
• Something
missing in our
logic
computer simulations…..
• My contribution: Supersonic turbulence doesn’t exist
• Dissipates immediately in shock waves
• Simulations: demonstrated this …even MHD waves
interact and dissipate on a ** sound crossing time **.
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CLOUDS ARE EPHEMERAL!
In a few million years:
Young stars condense out of clouds
Clouds form, evolve, dissipate
Similar properties……….…similar equations…
Opaque,
condensations (rain, grains),
turbulent,
ephemeral
low efficiency…..
• Most of a cloud is dispersed
• Only a few per cent is bound into stars
• Material is recycled 30 times
• Star formation is ongoing ( rate gradually slows )
The Revolution
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Rapid conception - turbulence
The Birth: the protostar
Feedback from powerful jets:
Emerge from giant clouds in clusters
Planets and Brown Dwarfs appear
ephemeral clouds
high accretion
strong extraction
spatial distribution
mass distribution
Turbulence v. Gravity
Feedback + Regulation + Interaction + Triggering
within a Nested System
Generates a COMPLEX SYSTEM
Out of which stars EMERGE
What we know we know….
• There are known knowns.
• These are things we know that we know.
• There are known unknowns.
• That is to say, there are things that we know we don't
know.
• But there are also unknown unknowns.
• There are things we don't know we don't know.
Donald Rumsfeld
Feb 12, 2002
Philosophy of science….
• UU to KU: pure thought, serendipitous observation,
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emergent phenomena ?
• KU to KK: systematic scientific methods
• Conjecture:
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UU = KU/KK
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Suggests: there are many
• Unknown Unknowns remaining in Star Formation