supernovae - smu physicsfusion • means by which stars generate energy • resulting mass less than...

SUPERNOVAE Daniel Rostro PHYS 3305 Fall 2014

Topics • Supernovae

•  Types 1a and II

• Processes •  Fusion •  Life cycle of star

• Nucleosynthesis •  Neutron capture

• Application •  Standard candles

2 Daniel Rostro PHYS 3305

Definition


Hubblesite.org

More Precise Definitions

Type Ia

• Binary star systems • White dwarfs • Do not exhibit hydrogen

spectral lines

Type II

• Size limitations •  At least 8x mass of Sun

• Exhibit hydrogen spectral lines


PROCESSES


Fusion • Means by which stars generate energy • Resulting mass less than sum of masses of individual

nuclei •  Products more tightly bound than the reactants •  Increase in kinetic energy •  Exothermic •  This energy fights against the force of gravity •  Produces energy and somewhat heavier nuclei


Fusion •  Ex: proton-proton cycle

•  0.5 MeV carried away by neutrinos •  26.2 MeV in core as thermal energy

7

1: 11H + 1

1H→ 2

1H + 0

+1β + v Q = 0.42 MeV

2 : 21H + 1

1H→ 3

2He + γ Q = 5.48 MeV

3: 32He+ 3

2He→ 4

2He+ 1

1H + 1

1H Q = 12.9 MeV

Q = 2(0.42 MeV) + 2(1.02 MeV) + 2(5.48 MeV) + 12.9 MeV = 26.7 MeV

4 11H + 2e− → 4

2He+ 2v+ 6γ

Daniel Rostro PHYS 3305

Life Cycle • Hydrostatic equilibrium • Hydrogen burned fastest at center of star •  Fuel eventually runs out

•  10 billion years into main sequence •  Helium core

• Outer layers continue fusion process •  Temperature too low for Helium burning

•  108 K required for Helium fusion •  Must overcome repulsion


Life Cycle Contd. • Core shrinks and rises in temperature

•  Heats surrounding layers •  Higher fusion rate

• Outer layers expand in size • Red giant

•  About as large as Mercury’s orbit


Life Cycle Contd. • Helium fusion begins a few hundred million years after

leaving main phase •  Triple Alpha Process •  Formation of carbon core • Expansion – Red supergiant •  600 million K required for next fusion reaction • White dwarf


Type Ia Supernovae/White Dwarfs • Very dense • No nuclear activity – electron degeneracy pressure • Will continue on unless part of binary star system

•  Stars orbiting about common COM

• Accreditation of matter •  Hydrogen and Helium gas

• Chandrasekhar mass – 1.4 solar masses •  If exceeded, degenerate electrons cannot withstand pressure

• Core contracts and temperatures rise • Carbon fusion begins • Star explodes


Type II Supernova • Stars with large mass fuse elements heavier than C and O • Accelerated evolution

• Star develops layers of heavier elements


cse.ssl.berkeley.edu

Type II Supernova • Energy is required to fuse Iron (Endothermic)

•  Iron very tightly bound; highest binding energy per nucleon

• Star fuses heavier elements until Iron •  Fe core develops •  Loss of equilibrium •  Star implodes


Type II Supernova • Core temperature about 10 billion K • Photons break nuclei apart – photodisintegration • Photodisintegration cools core

•  Core shrinks even faster

• Shrinking core forces protons and electrons together •  Neutrons and neutrinos form •  Neutrino a “noble” particle – carries away energy


Type II Supernovae • Neutrons pushed close together

•  Neutron degeneracy pressure

• Core rebounds • Shock wave blasts outer layers

•  Elements thrown into outer space


Nuclosynthesis • Helium capture • Silicon-28

• Core temperature of 3 billion K

• Photodisintegration • Alpha Process

• Results in Iron core • Neutron capture

• Heavier nuclei result as neutrons are absorbed

Daniel Rostro PHYS 3305 16

Astronomy Today Chaisson and McMillan

Neutron Capture • S-process

•  Neutrons available inside star; by-products of reactions •  Experience no repulsion – neutral charge •  Iron nucleus accumulates mass as more neutrons are absorbed

• R-process •  S-process produces nuclei up to bismuth •  Heavier nuclei decay rapidly to bismuth •  R-process occurs during supernova blast •  Numerous neutrons available as nuclei are broken apart •  Rapid uptake of neutrons allows for the “creation” of nuclei heavier

than bismuth

Daniel Rostro PHYS 3305 17

APPLICATION


Standard Candles • The Chandrasekhar Limit tells us the mass of a type 1a supernova star.

• As a result, luminosities of SNIa may be taken to be a standard ruler for distance measurements

• Using the known luminosity we can calculate distance using the inverse square law


wigglez.swin.edu.au

QUICK HISTORY


Betelgeuse • Betelgeuse is about 7 million years old.

• About 600 light years away •  May have already

exploded! • Kepler’s Supernova

•  1604 •  Last observable supernova

in our galaxy •  Visible during day for a

couple of weeks •  13,000 light years away


Wikipedia.org

Conclusion • Stars may “die” in a supernova explosion depending on

mass and surrounding conditions. • Powerful nuclear reactions inside stars give us the heavier

elements we find throughout the universe • Supernovae have a practical application as standard

candles to calculate distances across the universe •  “The nitrogen in our DNA, the calcium in our teeth, the

iron in our blood, the carbon in our apple pies were made in the interiors of collapsing stars. We are made of star stuff.” – Carl Sagan


Sources •  Images

•  Picture Album: A String of 'Cosmic Pearls' Surrounds an Exploding Star. (n.d.). Retrieved November 9, 2014, from http://hubblesite.org/gallery/album/star/supernova/pr2007016w/

•  Massive Red Supergiant. (n.d.). Retrieved November 8, 2014, from http://cse.ssl.berkeley.edu/bmendez/ay10/2000/cycle/massive.html

•  (n.d.). Retrieved November 8, 2014, from http://commons.wikimedia.org/wiki/File:Betelgeuse_position_in_Orion.png

•  (n.d.). Retrieved November 6, 2014, from https://wigglez.swin.edu.au/site/image1_files/ CandleRulerWide_2.jpg

•  Chaisson, Eric, and S. McMillan. Astronomy Today. 4th ed. Upper Saddle River, N.J.: Prentice Hall, 2002. Print.

•  Chandra :: Field Guide to X-ray Sources :: Supernovas & Supernova Remnants. (n.d.). Retrieved November 5, 2014, from http://chandra.harvard.edu/xray_sources/supernovas.html

•  Harris, R., & Harris, R. (2008). Modern physics (Second ed.). San Francisco: Pearson/Addison Wesley.

•  Imagine the Universe -- Advanced Science. (n.d.). Retrieved November 5, 2014, from http://imagine.gsfc.nasa.gov/docs/science/advanced_science.html

•  Kepler's Supernova. (2014, January 11). Retrieved November 7, 2014. •  Stellar Death. (n.d.). Retrieved November 7, 2014, from http://abyss.uoregon.edu/

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