Transcript Star Formation - University of Redlands

Star Formation
A Star is Born
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Goals
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What is there between the stars?
What are dust clouds?
What are nebulae?
How do these lead to the formation of star?
– Where do baby stars come from?
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The Stuff Between Stars
• Space isn’t empty.
• Interstellar Medium – The gas and dust between
the stars.
All the interstellar gas and dust in a volume the size of the Earth only
yields enough matter to make a pair of dice.
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The Distribution
• Picture the dust under your bed.
– Fairly uniform thin layer
– Some small clumps
– Occasional big complexes
• Interstellar dust and gas is the same.
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Dust
• Space is dirty.
• Dust blocks or scatters
some light.
• Result: black clouds and
patterns against the
background sky.
• But what light gets
through, and what light
doesn’t?
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Absorption and Scattering
• Q: Why are sunsets red?
• Light is absorbed or scattered by objects the
same size or smaller than its wavelength.
• Dust grains = wavelength of blue light
• Dust clouds:
– Opaque to blue light, UV, X-rays
– Transparent to red light, IR, radio
• A: Whenever there is a lot of dust between
you and the Sun, the blue light is absorbed or
scattered leaving the only the red light.
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Interstellar Reddening
• Same thing with
dust clouds in
space.
• Since space is full
of dust, the farther
away stars are, the
redder they look.
• Enough dust and
eventually all
visible light is
scattered or
absorbed.
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Dust and IR
• In a dark dust cloud:
– Even though all visible light may be gone, we can
still use IR.
– If dust is warm, IR will show its blackbody
emission.
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The IR Universe
Orion - visible
Orion – by IRAS
And allows us
to see dust
where we
wouldn’t
otherwise
expect it.
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The Trifid Nebula – copyright Jason Ware
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Interstellar Gas
• In Lab 2 we talked about spectral lines and how
they apply to hot and cool gases.
• Let’s look at some hot and cool gases in space.
Ha emission nebulae
Copyright - Jason Ware
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Horsehead
Nebula –
copyright Arne
Henden
Dust obscuring Ha emission nebula
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Orion Nebula –
copyright Robert Gendler
• In order for the hydrogen to emit light, the atoms
must be in the process of being excited.
• The energy for the excitation comes from very hot
stars (O and B stars) within the cloud.
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Cold Dark Clouds
• If dust clouds block
light, then inside
thick dust clouds
there should be no
light at all.
• Without light, there
is little energy.
• With little energy,
any gas inside is
very, very cold.
• Inside molecules
can form.
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Gravity vs. Pressure
• Stars and other interstellar
material are in a perpetual battle
between forces pulling in (gravity)
and forces pushing out (pressure).
• Gravity comes from the mass of the
cloud or star.
• Pressure comes from the motion of
the atoms or molecules.
– Think of hot air balloons.
– The hotter the air, the bigger the balloon.
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Star Formation
• Remember lecture 4:
HOTTER
COOLER
• Cold interstellar clouds:
No heat = no velocity = no outward pressure.
Gravity wins.
• Gas begins to contract.
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How to Make a Star
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1. The Interstellar Cloud
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Cold clouds can be tens of parsecs across.
Thousands of times the mass of the Sun.
Temperatures 10 – 100 K.
In such a cloud:
– Something makes a region denser than
normal.
– Force of gravity draws material to denser
region.
– Gravitational collapse begins.
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Orion Nebula – copyright Robert Gendler
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Contracting Fragments
• Cloud about the size of solar system.
• In the center:
– Collapsing material continues to heat up.
– Density causes heat to be retained.
• Higher density makes center opaque.
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Eagle Nebula –
copyright J. Hester
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2. Protostar
• The central opaque part is called a protostar.
• Mass increases as material rains down on it.
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•Visible and IR image of the hot protostars in the Orion Nebula.
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…and the Nebula?
• Cloud around the
protostar spins faster.
• Flattens to a disk.
– Pizza dough.
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Planetesimals
• Dust and gas
condense onto
dust grains.
• Small clumps
grow bigger.
• Bigger clumps
have more mass
and attract more
matter.
• Planetesimals
become the
building blocks
of the planets.
Orion Nebula – Copyright O’Dell and Wong
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3. T Tauri Phase
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Protostar still shrinks: 10x the Sun.
Still heats up: surface = 4000 K
Core temp = 5,000,000 K
Violent surface activity creates
strong winds that blow material
away near the protostar’s surface.
• Clear away the dust and gas
between planets.
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A Star is Born
• Time: 40- 50 million years since the collapse started.
• Radius: 1,000,000 km (Recall the Sun = 700,000 km)
• Core temp: 10,000,000 K (Sun = 15,000,000 K)
– Surface temp = 4500 K
• Fusion begins in core.
• Energy released creates the pressure needed to counter
the contraction from gravity.
• Contraction ends!
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An H-R Life-Track
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The Main Sequence
• For the Sun:
– While it took 40 – 50
million years to get here,
the new star will spend the
next 10 billion years as a
main sequence star.
• Bigger Stars:
– Everything goes quicker.
• Smaller Stars:
– Everything longer.
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Now what?
• The mass of the star
that is formed will
determine the rest of its
life!
• Recall: the more
massive the star, the
more pressure in the
core.
• The more pressure, the
more fusion.
• More fusion:
– More energy produced
– Hotter
– Shorter life span
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Open
Clusters
• These are the new stars.
• Small groups of young
stars.
• Slowly drifting apart.
Jewel Box – copyright MichaelBessell
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Homework #7
• For 10/16:
• Read B16.3 – 16.5, B17.1 – 17.3
• Do:
– Ch16 : Review Questions 9, 18, Problem 1
– Ch17: Review Question 1, Problem 4
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