Download Stellar Birth - Chabot College

Star Stuff
I can hear the sizzle of newborn stars,
and know anything of meaning, of the
fierce magic emerging here. I am
witness to flexible eternity, the evolving
past, and know I will live forever, as
dust or breath in the face of stars, in
the shifting pattern of winds.
Joy Harjo (1951 – )
from Secrets From the Center of the World
WHAT DO YOU THINK?
1. How do stars form?
2. Are stars still forming today?
If so, where?
3. Do more massive stars shine longer than
less massive ones? What is the reason?
Key Questions to Answer!
What is the interstellar medium made of?
How do stars form? How do we know?
How will our Sun evolve as a star? What
will its final state be? Compare its
predicted evolution to that of higher-mass
stars. How do they end? How do we
know?
The “Dark
Tower” in
Scorpius
The Pillars of
Creation near Orion
Pleiades
in Visible
light
Pleiades in
IR light
“false” colors,
applied to
match
temperatures
The Inter-stellar Medium
Observe/Research
Where do stars form?
What are they made of?
What properties are common? Rare?
Create THEORY of star formation
Test hypotheses predicted by the theory
The ISM: How do we know?
Where do stars form?
Visible, IR, Microwave, Radio observations
What are they made of?
Spectra
What properties are common? Rare?
HR Diagram, Mass, Number density, Location
Test hypotheses predicted by theory
Visible, IR, Microwave, Radio observations
ISM: Where do stars form?
We observe:
Visible “extinction nebulae” block
background light
Visible emission nebulae form hot gas
Visible signs of dust scattering and
dimming and reddening starlight
Extinction
nebulae from
gas/dust
blocking light
Emission
nebulae from
gas emitting
light
Extinction
nebulae from
gas/dust
blocking light
Reflection
nebulae from
dust
scattering
blue light
The Horsehead
Nebula
Dust grains also cause “interstellar reddening”
Dust grains also cause “interstellar reddening”
Learning About Stellar Lives
How can we know anything?
Create HR diagrams of clusters of stars
Assume
Same relative distance  comparing relative
brightness is fair
Same relative age  comparing masses and
types of stars is fair
Pleiades
“Open”
Cluster in disk
of Milky Way
Galaxy
Pleiades
HR
Diagram
Stars of all
types &
masses
Another
Star Cluster
Stars of all
types &
masses
NGC 2264
HR
Diagram
Some objects
not yet formed
as stars!
“T-Tauri
Protostars”
Observational evidence of “protostars”
Protostars seem to appear in CLUSTERS
New Stars & Brown Dwarfs that will never be…
An
actual
Brown
Dwarf!
Supermassive stars lead very unstable lives!
Pressure from fusion literally blows outer layers away!
One of the
largest
stars
known….
5,000,000
times
brighter
than our
Sun!
Star Formation in 4 Steps!
Start with Large Cloud of Gas & Dust
1. Shock creates fragments & “blobs”
2. Gravity creates clusters of star “seeds”
3. Individual blobs heat up and glow as
protostars
4. Protostars start fusion in cores
5. ♫ A star is born! ♫
Star Formation in 4 Steps!
Start with Large Cloud of Gas & Dust
Giant molecular clouds
Raw materials to form 100’s, 1000’s, or
millions of stars in clusters.
Mass & Location affect # of stars to be formed
Temperature affects rate of formation
Observations supporting this phase:
Radio telescopes, Microwave Maps
Star Formation in 4 Steps!
1. Shock the cloud – break it into fragments
Gravitational Forces (galaxies, mergers,
collisions)
Stellar winds of new massive stars
Supernovae of massive stars that form fast
Observations supporting this phase:
HST views of Eagle Nebulae
Star Formation in 4 Steps!
2. Gravity takes over, creating clusters of
what will eventually be stars
OB Associations
Open Clusters
Globular Clusters
Observations supporting this phase:
Microwave/IR observations of warming
regions
Star Formation in 4 Steps!
3. Individual blobs heat up, rotate, and glow
as protostars




Contracting into disks
Shining by gravitational energy (not fusing!)
Larger than “real” stars, & cooler
Develop jets of radiation from poles
Observations supporting this phase:
T-Tauri stars
Disks & Jets in
Protostars
Star Formation in 4 Steps!
4. A star is born!
 Fusion of Hydrogen to Helium starts in core
 Stops Contracting
 Hydrostatic Equilibrium Established
 A “main sequence” star
But….
Will it have planets?
Star Formation in 4 Steps!
Lives of Main Sequence Stars
Where a star is plotted depends on mass
O dwarfs (O V) are most massive
M dwarfs (M V) are least massive
ALL Main Sequence stars fusing H  He
Lives of Main Sequence Stars
ALL Main Sequence stars fusing H  He
 The star is stable, in balance
Gravity (in) vs. force (out) from gas pressure
and radiation pressure from fusion reactions
Stellar Evolution
Building models of what
happens to stars
Low mass (0.08 to 0.4 Msun
Medium mass (0.4 to 4+ Msun
Higher Mass (5+ to >100 Msun
Low mass star evolution
(~8% to ~40% of our Sun’s Mass)
Slower fusion reaction rate
Cooler surface temp (red stars)
Low Luminosity
Longer Lives
“Economy models!”
Low mass star evolution models
Totally “convective” inside!
(mixed throughout)
convert ALL Hydrogen into Helium
don’t develop a Helium “core”
Eventually collapse to white dwarf
Low mass stars models predict mixing inside
to convert all H to He
Medium Mass
40% to 400% of Sun’s Mass
Life like our Sun – about 10 Billion years
Slowly develop Helium core
Helium “ash” not fusing --- yet!
Surrounded by Hydrogen still fusing
Medium Mass
40% to 400% of Sun’s Mass
Core collapses, becomes “degenerate”
Star swells into Red Giant
Eventual Helium FLASH
as fusion of He  Carbon starts up!
A “new” life– for a short time!
High Mass Stellar Evolution
Much greater fusion rate, MUCH brighter,
MUCH, MUCH shorter lived stars
Quickly reach Helium Core stage, and can
start fusing He  Carbon, develop C core,
then repeat with heavier and heavier
atoms
High Mass Stellar Evolution
“Onion Skin” model of heavier & heavier
shells
Fuse until Iron core formed…
Boom!