Stars, Their Lives, And The
Stuff In Between
Sarah Silva
Program Manager
Sonoma State University NASA
Education and Public Outreach
The NASA E/PO Program at
Sonoma State University
• A group of seven people working collaboratively
to educate the public about current and future
NASA high energy astrophysics/astronomy
missions.
Swift
• Led by Prof. Lynn Cominsky
GLAST
XMM-Newton
What do we know about
stars?
Life Cycles of Stars
Classifying Stars
Stars spend
most of their
lives on the
Main Sequence
Hertzsprung-Russell diagram
Stars and Balloons
• Volunteers Please
Stars and Balloons
•
•
•
•
•
Imagine we have:
12 - Red Balloons
12 - Yellow Balloons
4 - White Balloons
2 - Blue Balloons
OR
• Roughly 80% red and yellow, 15% white,
and 5% blue.
Preparation:
• Place 1 wooden bead inside each red and
yellow balloon.
• Place 1 marble inside each white balloon.
• Place 1 ball bearing inside each blue
balloon.
Stars and Balloons
• Red Balloons ↓0.4 Solar Mass (2/5 the mass of
our Sun): Red stars
• Yellow Balloons 1 Solar Mass (the mass of our
Sun): Yellow Stars
• White Balloons 3 Solar Masses (3 times the
mass of our Sun): White Stars
• Blue Balloons 9 Solar Masses (9 times the
mass of our Sun): Blue Stars
• Please blow up your balloon until it has a 3 inch
diameter.
5 Million Years
Red Balloons
Yellow Balloons
White Balloons
Blue Balloon
↓0.4 Solar Mass (2/5
the mass of our Sun):
Red stars
1 Solar Mass (the
mass of our Sun):
Yellow Stars
3 Solar Masses (3
times the mass of our
Sun): White Star
9 Solar Masses (9
times the mass of our
Sun): Blue Stars
Wait. Do not change
diameter of balloon.
Wait. Do not change
diameter of balloon.
Wait. Do not change
diameter of balloon.
Blow slightly more air
into balloon.
10 Million Years
Red Balloons
Yellow Balloons
White Balloons
Blue Balloon
↓0.4 Solar Mass (2/5
the mass of our Sun):
Red stars
1 Solar Mass (the
mass of our Sun):
Yellow Stars
3 Solar Masses (3
times the mass of our
Sun): White Star
9 Solar Masses (9
times the mass of our
Sun): Blue Stars
Wait.
Wait.
Blow up a little more
Blow up star as fast
and as much as you
can. When star is fully
inflated, -a supernova.
500 Million Years
Red Balloons
Yellow Balloons
White Balloons
Blue Balloon
↓0.4 Solar Mass (2/5
the mass of our Sun):
Red stars
1 Solar Mass (the
mass of our Sun):
Yellow Stars
3 Solar Masses (3
times the mass of our
Sun): White Star
9 Solar Masses (9
times the mass of our
Sun): Blue Stars
Wait
Wait (note: planets are
forming)
Continue to slowly
inflate star. As it gets
bigger, star cools, so
color it yellow and red
(make squiggles on
surface with markers).
This popped star has
become a black hole;
all of the super nova
remnants can be
thrown out into space.
1 Billion Years
Red Balloons
Yellow Balloons
White Balloons
Blue Balloon
↓0.4 Solar Mass (2/5
the mass of our Sun):
Red stars
1 Solar Mass (the
mass of our Sun):
Yellow Stars
3 Solar Masses (3
times the mass of our
Sun): White Star
9 Solar Masses (9
times the mass of our
Sun): Blue Stars
Wait
Blow up a little bit.
Quickly blow up star
until fully inflated;
pop balloon. Make
sure to catch marble
Still black hole!
8 Billion Years
Red Balloons
Yellow Balloons
White Balloons
Blue Balloon
↓0.4 Solar Mass (2/5
the mass of our Sun):
Red stars
1 Solar Mass (the
mass of our Sun):
Yellow Stars
3 Solar Masses (3
times the mass of our
Sun): White Star
9 Solar Masses (9
times the mass of our
Sun): Blue Stars
Wait
Blow up more. The
star is getting cooler,
so color it red with
marker. It is now a
supergiant.
This star has
exploded. Holding on
to neutron star
(marble), throw
supernova remnants
into space. Place
remnants in a recycle
bin to demonstrate
stellar gas is recycled
into new star matter.
Still black hole
10 Billion Years
Red Balloons
Yellow Balloons
White Balloons
Blue Balloon
↓0.4 Solar Mass (2/5
the mass of our Sun):
Red stars
1 Solar Mass (the
mass of our Sun):
Yellow Stars
3 Solar Masses (3
times the mass of our
Sun): White Star
9 Solar Masses (9
times the mass of our
Sun): Blue Stars
Wait
Blow up a little more.
Outer envelope
dissolves, so cut up
balloon. The inside
bead becomes a white
dwarf, and the bits of
balloon represent the
planetary nebula.
Neutron star
Still black hole
Reprise: the Life Cycle
Sun-like Stars
Massive Stars
Molecular clouds and protostars
• Giant molecular clouds are
very cold, thin and wispy–
they stretch out over tens of
light years at temperatures
from 10-100K, with a warmer
core
• They are 1000s of time more
dense than the local
interstellar medium, and
collapse further under their
own gravity to form
protostars at their cores
BHR 71, a star-forming cloud
(image is ~1 light year across)
Protostars
• Orion nebula/Trapezium stars (in the sword)
• About 1500 light years away
HST/ 2.5 light years
Chandra/10 light years
Stellar nurseries
HST/Eagle
Nebula in
M16
• Pillars of
dense gas
• Newly born
stars may
emerge at
the ends of
the pillars
• About 7000
light years
away
HR Diagram again as a reminder
Main Sequence Stars
• Stars spend most of their lives on the “main sequence”
where they burn hydrogen in nuclear reactions in their
cores
• Burning rate is higher for more massive stars - hence
their lifetimes on the main sequence are much shorter
and they are rather rare
• Red dwarf stars are the most common as they burn
hydrogen slowly and live the longest
• Often called dwarfs (but not the same as White Dwarfs)
because they are smaller than giants or supergiants
• Our sun is considered a G2V star. It has been on the
main sequence for about 4.5 billion years, with another
~5 billion to go
Pro Fusion or Con Fusion?
• The core of the Sun is 15 million degrees
Celsius
• Fusion occurs 1038 times a second
• Sun has 1056 H atoms to fuse
• 1018 seconds = 32 billion years
• 2 billion kilograms converted every second
• Sun’s output = 50 billion megaton bombs per
second
Don’t Let the Sun Go Down on Me
1018 seconds is a long time…
but it’s not forever.
What happens then?
The Beginning Of The End:
Red Giants
After Hydrogen is exhausted in core...
Energy released from nuclear fusion
counter-acts inward force of gravity.
Core collapses,
and kinetic energy of collapse
converted into heat.
This heat expands the outer layers.
Meanwhile, as core collapses,
Increasing Temperature and Pressure ...
More Fusion !
At 100 million degrees Celsius, Helium
fuses:
3 (4He) --> 12C + energy
(Be produced at an intermediate step)
(Only 7.3 MeV produced)
Energy sustains the expanded outer
layers of the Red Giant
Stellar evolution made simple
Puff!
Bang!
BANG!
Stars like the Sun go gentle into that good night
More massive stars rage, rage against the dying of the light
How stars die
• Stars that are below about 8 Mo form red giants
at the end of their lives on the main sequence
• Red giants evolve into white dwarfs, often
accompanied by planetary nebulae
• More massive stars form red supergiants
• Red supergiants undergo supernova
explosions, often leaving behind a stellar core
which is a neutron star, or perhaps a black hole
Red Giants and Supergiants
Hydrogen
burns in outer
shell around
the core
Heavier
elements burn
in inner shells
Fate of high mass stars
• After Helium exhausted, core collapses again
until it becomes hot enough to fuse Carbon
into Magnesium or Oxygen.
12C + 12C --> 24Mg
OR
12C + 4H --> 16O
• Through a combination of processes,
successively heavier elements are formed
and burned.
Heavy Elements from Large
Stars
• Large stars also fuse Hydrogen into
Helium, and Helium into Carbon.
• But their larger masses lead to higher
temperatures, which allow fusion of
Carbon into Magnesium, etc.
Supernova !
Crab nebula and pulsar
X-ray/Chandra
Neutron Stars and Pulsars
Neutron Stars and Pulsars
If neutron stars are made of neutral particles, how can
they have magnetic fields?
• Neutron stars are not totally made of neutrons-- the
interiors have plenty of electrons, protons, and other
particles.
• These charged particles can maintain the magnetic field.
• Plus, a basic property of magnetism is that once a
magnetic field is made, it cannot simply disappear.
• Stars have magnetic fields because they are composed
of plasma, very hot gas made of charged particles.
Magnetic Globe Demo
A Burst By Any Other Name…
• Neutron star: dense core
leftover from a supernova
• Possess incredibly strong
magnetic fields
• Soft Gamma Ray
Repeater: violent energy
release due to starquake
• Accretion: neutron star
draws matter off binary
companion
• Matter piles up,
undergoes fusion: bang!
• Cycle repeats: X-Ray
Burster
Flash!
The fading afterglow, seen for the first time in X-rays
Swift Mission
Launched November 20, 2004
• Burst Alert
Telescope (BAT)
• Ultraviolet/Optical
Telescope (UVOT)
• X-ray Telescope
(XRT)
Swift Mission
• Will study Gamma-Ray Bursts with “swift”
response
• Survey of “hard” X-ray sky
• Launched November 20, 2004
• Nominal 2-year lifetime
• Will see ~150 GRBs per year
Birth of a Black Hole
• Long bursts (>2
seconds) may be
from a hypernova: a
super-supernova
• Short bursts (<2 s)
may be from merging
neutron stars
• Both create nature’s
vacuum cleaner: a
black hole
Gamma-ray Bursts
Either way you look
at it – hypernova
or merger model
GRBs signal the
birth of a black
hole!
What Is A Black Hole?
– Not just a vacuum cleaner
– If you take an object and squeeze it down in
size, or take an object and pile mass onto it,
its gravity (and escape velocity) will go up.
Black Hole Structure
• Schwarzschild radius
defines the event
horizon
• Rsch = 2GM/c2
• Not even light can
escape, once it has
crossed the event
horizon
• Cosmic censorship
prevails (you cannot see
inside the event horizon)
Schwarzschild BH
Black Hole Space Warp
•
Record the following questions based on your
observations.
1. What do the moving balls represent?
2. What does the weight represent?
3. What happened to the balls?
4. What does the blue latex material
represent?
5. What happens to the material when the
bouncy balls roll around?
Masses of Black Holes
• Primordial – can be any size, including very small
(If <1014 g, they would still exist)
• “Stellar-mass” black holes – must be at least 3 Mo
(~1034 g) – many examples are known
• Intermediate black holes – range from 100 to 1000
Mo - located in normal galaxies – many seen
• Massive black holes – about 106 Mo – such as in
the center of the Milky Way – many seen
• Supermassive black holes – about 109-10 Mo located in Active Galactic Nuclei, often
accompanied by jets – many seen
How Do Black Holes Form?
• Stellar-mass black holes
– Supernova: an exploding star. When a star
with about 25 times the mass of the Sun ends
its life, it explodes.
– called a “stellar-mass black hole,” or a
“regular” black hole
– Stellar-mass black holes also form when two
orbiting neutron stars – ultra-dense stellar
cores left over from one kind of supernova –
merge to produce a short gamma-ray burst.
Where Are Black Holes Located?
• Let’s think….
• They form from exploded stars…
• We have one at the center of the Milky
Way….
• The nearest one discovered is still 1600
light years away
• Black holes are everywhere!
Evidence
• This shows ten
years worth of
Prof. Ghez’ data at
2.2 microns of the
stars orbiting
around a 4 million
solar mass black
hole at the center
of the Milky Way.
• It also shows the
star’s orbits
extrapolated into
the future
Note: Stars S0-2 and S0-16 provide the
best data
Supermassive Black Holes
• Normal galaxy
– A system of gas, stars, and
dust bounded together by
their mutual gravity.
VS.
• Active galaxy
– An galaxy with an intensely
bright nucleus. At the
center is a supermassive
black hole that is feeding.
Galaxies and Black Holes
Jet
• Zooming in to see the
central torus of an
Active Galaxy.
Accretion disk
Black Hole
Resources
• 1st Section – Stellar Cycle Balloon Activity
– Adler Planetarium:
http://www.adlerplanetarium.org/education/teachers/pl
ans/gravity/9-12_gq5-1.shtml
• 2nd Section – Supernova and Magnetic Globe
– http://xmm.sonoma.edu/edu/supernova
• 3rd Section – Black Holes Space Time Warp
– http://glast.sonoma.edu/teachers/blackholes
– My Email: sarah@universe.sonoma.edu
• extra
The Supernova Connection
Afterglow faded like supernova
Data showed presence of gas like a stellar wind
Indicates some sort of supernova and not a NS/NS merger
GRB011121
Iron lines in GRB 991216
Chandra observations show link to hypernova
model when hot iron-filled gas is detected
from GRB 991216
Iron is a signature of a
supernova, as it is
made in the cores of
stars, and released in
supernova explosions
Hypernova
movie
• A billion trillion times the power from the Sun
• The end of the life of a star that had 100 times
the mass of our Sun
Catastrophic Mergers
• Death spiral of 2 neutron stars or black holes