Fusion, Explosions, and the Search for Supernova Remnants

1. Fusion, Explosions, and the Search for Supernova Remnants Crystal Brogan (NRAO)

2. Nuclear Reactions • Fission reactions split atomic nuclei • Used in nuclear reactors on earth • Fusion reactions fuse atomic nuclei • The energy in stars comes from fusion

3. Energy Production • All stars produce energy by nuclear fusion • Nuclear fusion can only produce energy from elements with the number of protons + neutrons (atomic weight) less than Iron=56 otherwise it takes energy. • The sun isn’t hot enough to fuse elements with higher atomic weight than Hydrogen and Helium # protons + neutrons

4. Periodic Table of Elements

5. What will happen to the Sun when it runs out of fuel? All stars are in a constant tug-of-war between gravity inward and the energy outward from fusion Artist’s conception of the formation of a white dwarf and the Helix Nebula

6. Optical HST Images of Planetary Nebula The Ring Nebula The Hourglass Nebula The Stingray Nebula The Cat’s Eye Nebula

7. The Hertzsprung-Russell (H-R) Diagram Main Sequence: The normal part of a star’s life when it is burning Hydrogen in its core. Luminosity Our sun Temperature and Mass Stars have differenttemperatures, differentluminosities, and differentsizes = spectral type (OBAFGKML)

8. What if the star is very massive > 8 x M sun? • Since they are MUCH hotter can also fuse elements up to Iron • They use up all their fuel very quickly – within a few million years compared to 10 billion years for our Sun. It takes energy to fuse any element heavier than iron once the fuel is gone gravity wins…

9. What causes the explosion? Gravity • In ~1/10 second, nearly all of the iron in the core is destroyed, undoing millions of years of fusion • Core collapses until it becomes as dense as material can possibly be and a neutron star or black hole is formed • Infalling material from outer layers bounces off dense core • In tremendous release of energy, elements heavier than iron are formed and are spread into space

10. Simulation of Supernova Explosion

11. Evolution with a companion

12. Over the next few days, the star will become about 100 million times brighter, often outshining all the other stars in the host galaxy combined.

13. The Famous Supernova of 1987: SN 1987A(closest supernova in recent history, ~160,000 l.y. away)

14. The Famous Supernova of 1987: SN 1987A(closest supernova in recent history, ~160,000 l.y. away)

15. Radio: Very Long Baseline Array Movie of Supernova 1993J in the Galaxy M81 Timeframe of movie is 9 years (~3 frames per year)

16. The Crab Nebula SNR from 1054 AD SNR E0102-72 Red: Radio Blue: X-rays Green: Optical What do Supernovae Look Like When They Get Older? They become Supernova Remnants (SNRs) SNR Cas A Exploded in ~1670 AD

17. How do we know this? • Massive O and B spectral type star counts • Abundance of Iron [Fe] • Observed supernova rate in the Local Group of Galaxies M51 Galaxy How Many Supernova Remnants are there in our Galaxy? • Up to the end of 2004, about 230 SNRs had been identified in our Galaxy from radio and X-ray observations • However, many more SNRs are expected in our Galaxy (> 1,000) than are currently known

18. So What’s the Deal? • Probably due to observational selection effects • Poor resolution (hard to distinguish one thing from another) • Poor sensitivity to faint objects • Effects are most severe toward inner Galactic plane Andromeda M51 Galaxy showing new Supernova

19. Why Should we Care? SNR Cas A • Important tests of our understanding of the star formation history of our Galaxy • Production of heavy elements  all elements heavier than iron on the Earth and in you come from supernova • Distribution of SNRs controls distribution of elements in the Galaxy and may be a key determinant of life on other planets M101 Galaxy

20. W28 Supernova Remnant 90cm VLA Mosaic resolution 42” Brogan et al. (2006) 11cm Bonn Survey resolution 260” M17 High Mass star forming region • Very Large Array 90cm (330 MHz) survey of 42 sq. degrees • 14 pointings, each observed for ~5 hours A Low Frequency View of the Inner Galactic Plane Reich et al. (1984)

21. Blue: VLA 90cm Green: Bonn 11cmRed: MSX 8 mm • Radio traces both thermal and non-thermal emission • Mid-infrared traces primarily warm thermal dust emission Finding the “Missing” Supernova Remnants 35 New SNRs discovered; a ~300% increase in this region and a 15% in the total number! Comparing different wavelength images is the key because they show different things… VLA 90 cm Brogan et al. (2006) MSX 8 mm Price et al. (2001) • Radio traces both thermal and non-thermal emission • Mid-infrared traces primarily warm thermal dust emission

22. Close-Up Multi-wavelength View Blue: VLA 90cm (Brogan et al. 2006)Green: VLA + SGPS 20cm (McClure-Griffiths et al. 2005)Red: MSX 8 mm (Price et al. 2001)

23. Summary • Stars shine through nuclear fusion • Stars make all elements heavier than Hydrogen • When they run out of fuel : • Low mass stars like the sun will turn into white dwarfs while their outer layers form planetary nebula • Much more massive stars produce a supernova and supernova remnants • We have not yet found the expected number of Galactic supernova remnants • Comparing images at different frequencies is the key to finding more • These results (35 new SNRs) suggest that a similar study of a larger part of the Galactic plane would find up to ~500 SNRs

25. Sources of Stellar Energy The “proton-proton” cycle =fusion of 4 Hydrogen atoms into one Helium atom: • 4 H atoms = 6.693x10-27 kg • 1 He atom = 6.645x10-27 kg Difference= 0.048x10-27 kg, converted to energy E=mc2 • All stars produce energy by nuclear fusion of hydrogen into helium • The sun isn’t hot enough to fuse heavier elements A star is in a constant tug-of-war between gravity inward and the energy outward from fusion

26. Massive Stars can also usethe Carbon-Nitrogen-Oxygen Cycle The CNO cycle requires much higher temperatures, but it also produces much more energy per second. Only possible in high mass stars because they are MUCH hotter The most massive stars only live a few million years compared to 10 Billion for our sun!