Transcript VLA 90 cm Brogan et al. (2006)

Fusion, Explosions, and the Search for
Supernova Remnants
Crystal Brogan (NRAO)
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
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
Periodic Table of Elements
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
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Artist’s conception of the formation of a white dwarf
and the Helix Nebula
Optical HST Images of Planetary Nebula
The Hourglass Nebula
The Ring Nebula
The Stingray Nebula
The Cat’s Eye Nebula
The Hertzsprung-Russell (H-R) Diagram
Luminosity
Main Sequence:
The normal part
of a star’s life
when it is burning
Hydrogen in its
core.
Our sun
Temperature and Mass
Stars have different temperatures, different luminosities, and
different sizes = spectral type (OBAFGKML)
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…
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
Simulation of Supernova Explosion
QuickTime™ and a
YUV420 codec decompressor
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Evolution with a companion
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.
The Famous Supernova of 1987: SN 1987A
(closest supernova in recent history,
~160,000 l.y. away)
The Famous Supernova of 1987: SN 1987A
(closest supernova in recent history,
~160,000 l.y. away)
Radio: Very Long Baseline Array Movie of
Supernova 1993J in the Galaxy M81
Timeframe of movie is 9 years (~3 frames per year)
What do Supernovae Look Like When They Get Older?
 They become Supernova Remnants (SNRs)
The Crab Nebula
SNR from 1054 AD
SNR Cas A Exploded in ~1670 AD
SNR E0102-72
Red: Radio Blue: X-rays Green: Optical
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
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
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
Why Should we Care?
 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
SNR Cas A
M101 Galaxy
A Low Frequency View of the Inner Galactic Plane
90cm VLA Mosaic resolution 42”
W28 Supernova
Remnant
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
Reich et al. (1984)
Finding the “Missing” Supernova Remnants
Comparing
different
wavelength images
is theincrease
key because
35
New SNRs
discovered;
a ~300%
in this
they show different things…
region
and a 15% in the total number!
VLA 90 cm Brogan et al. (2006)
MSX 8 mm Price et al. (2001)
Blue: VLA 90cm
Green: Bonn 11cm
Red: MSX 8 mm
• Radio traces both thermal and non-thermal emission
• Mid-infrared traces primarily warm thermal dust emission
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)
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
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
Massive Stars can also use
the 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!