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At the Heart of a Supernova
Sarah Silva
Program Manager
Sonoma State University E/PO
The NASA E/PO Program at Sonoma State University
• A group of eight people working collaboratively to educate the public about current and future NASA high energy astrophysics/astronomy missions.
• Led by Prof. Lynn Cominsky Swift
GLAST
XMM-Newton
What is XMM-Newton?• A joint NASA-European Space
Agency (ESA) orbiting observatory, designed to observe high-energy X-rays emitted from exotic astronomical objects such as pulsars, black holes, and active galaxies.
• XMM Newton Science Goals– When and where are the chemical
elements created?
– How does nature heat gas to X-ray emitting temperatures?
Launched in 1999!
What is GLAST?
• GLAST: Gamma-Ray Large Area Space Telescope
• Planned for launch in 2007
• GLAST has two instruments:
– Large Area Telescope (LAT)
– GLAST Burst Monitor (GBM)
• GLAST will look at many different objects within the energy range of 10keV to 300GeV.
LAT
GBM
Supernova !
Life Cycle of a Supernova
Stellar evolution made simple
Stars like the Sun go gentle into that good night
More massive stars rage, rage against the dying of the light
Puff!
Bang!
BANG!
Magnetic Fields Across the Universe
Magnetic Globe Demo
At the Heart of a Supernova• Experiment: Using the materials provided; design and
create a model of a pulsing neutron star. Describe it on the page provided.
• Suggested Materials:• Small laser lights• Diodes• Tape• Small batteries (3 V)• Modeling clay• Aluminum foil
You have 20 minutes to put your pulsar together and answer questions 18-27.
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.
Crab nebula and pulsar
X-ray/Chandra
Reprise: the Life Cycle
Sun-like Stars Massive Stars
HR Diagram
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
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 Educator Guide
Resources• XMM-Newton Education and Public
Outreach site: http://xmm.sonoma.edu
• Supernova and Magnetic Globe– http://xmm.sonoma.edu/edu/supernova
• GLAST Education and Public Outreach site: http://glast.sonoma.edu
• Downloadable GLAST materials for:– http://glast.sonoma.edu/teachers/teachers.html
My Email: [email protected]
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• Pillars of dense gas
• Newly born stars may emerge at the ends of the pillars
• About 7000 light years away
HST/EagleNebula in M16
Classifying Stars
Hertzsprung-Russell diagram
Stars spend most of their lives on the Main Sequence
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
1018 seconds is a long time…
but it’s not forever.
What happens then?
Don’t Let the Sun Go Down on Me
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
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
