# Presentation: 668425

## Just What is a Supernova?

- Prof. Lynn Cominsky
- Dept. of Physics and Astronomy
- Sonoma State University

## Types of Supernovae

- Type I
- No Hydrogen is observed
- Outer stellar layers are already missing prior to the explosion – due to binary system evolution?
- Found in elliptical and spiral galaxies
- Subgroups are Ia, Ib and Ic
- Type II
- Hydrogen is observed
- Probably from higher mass stars
- Found primarily in spiral galaxy arms

- SN1987A

## How stars die

- Single 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 Type II supernova explosions, often leaving behind a stellar core which is a neutron star, or perhaps a black hole

**Notes:**
The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the bright cluster stars. Low mass, faint, brown dwarfs have recently been found in the Pleiades. 

## Type II supernova animation

- Dana Berry/SkyWorks Digital/NASA

**Notes:**
The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the bright cluster stars. Low mass, faint, brown dwarfs have recently been found in the Pleiades. 

## Stars in binary systems

- In a binary star system consisting of a white dwarf and a main sequence star, the main sequence star will transfer matter to the white dwarf
- When the white dwarf reaches the “Chandresekhar limit” of 1.4 Mo, it can no longer support itself, and it implodes with a bright flash of energy released due to carbon and oxygen fusion inside the star

## Matter transfer in a binary system

- Matter transfers between white dwarf and more massive companion
- “Roche lobe”

- Blondin 1998

- John Blondin/NCSU

## Distances to Type Ia Supernovae 

- All Ias are due to implosion of 1.4 Mo white dwarfs, so they all have the same amount of fuel to burn and produce the same luminosity
- They therefore act like “standard candles”

**Notes:**
The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the bright cluster stars. Low mass, faint, brown dwarfs have recently been found in the Pleiades. 

## Distances to Type Ia Supernovae 

- Decay time of light curve is correlated to absolute luminosity
- Luminosity comes from the radioactive decay of Cobalt and Nickel into Iron
- Some Type Ia supernovae are in galaxies with Cepheid variables
- Good to 20% as a distance measure

**Notes:**
The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the bright cluster stars. Low mass, faint, brown dwarfs have recently been found in the Pleiades. 

## Supernova “CAT Scan”

- The energy spectrum of a supernova tells us in fine detail about its origin and properties.** **

- Over time the SN atmosphere expands and thins, allowing us to see every layer.

## Type Ia Supernova lightcurves

- Redshift measured tells us expansion factor (average distance between galaxies)

- Peak brightness tells us distance away (lookback time)

## Type Ia Supernovae and Cosmology

- Here is a typical supernova lightcurve and its spectrum
- Compare two distances to see if expansion rate has changed

- Measure shape of curve and peak distance

- Measure redshift  distance

## Type Ia Supernovae and Dark Energy

- Analyze lightcurves vs. redshifts for many Type Ia supernovae at redshifts z <2
- Observations of over 100 SN (over 7 years) by Perlmutter et al. and Schmidt et al. have showed that they are dimmer than would be expected if the Universe was expanding at a constant rate or slowing down (as was previously thought)
- This means that some unknown “dark energy” is causing the Universe to fly apart at ever-increasing speeds.

## Resources

- Imagine the Universe _[http://imagine.gsfc.nasa.gov](http://imagine.gsfc.nasa.gov/)_
- Eric Linder’s General talk on the History and Fate of the Universe _[http://epo.sonoma.edu/SNAP/education/presentations.html](http://epo.sonoma.edu/SNAP/education/presentations.html)_
-  Supernova Lab Activity from Lindsay Clark Bartolone (Princeton) _[http://www.astro.princeton.edu/~clark/SNLab.html](http://www.astro.princeton.edu/~clark/SNLab.html)_
- John Blondin’s numerical simulations of binaries
- _[http://www.physics.ncsu.edu/people/faculty_blondin.html](http://www.physics.ncsu.edu/people/faculty_blondin.html)_