ASTR 1040 Accel Astro: Stars

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ASTR 1040 Accel Astro Stars Galaxies
Cas A SNR VLA - radio

• Prof. Juri Toomre TA Nick Featherstone
• Lecture 17 Tues 13 Mar 07
• zeus.colorado.edu/astr1040-toomre

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Today in Bizarre-Land

• Massive stars end life with supernova explosion,
  leaving behind either neutron star or black hole
• Pulsars fast spinning neutron stars with fierce
  magnetic fields gradually slow down
• Synchrotron radiation makes the light seen as
  pulses and thus Crab nebula pulsar shines
  (and pulses) brightly in many wavelengths

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Things to do

• Respond to discussion (Thur) on we are made of
  star stuff, and how does it come about
• Observatory Night 4 tonight, 8pm (signup)
• Read 18.4 Black Holes carefully for Thur lecture
• Evening Review tomorrow 7-9pm, prepare for Second
  Mid-Term Exam on Fri 16 Mar (Review Sheet 2
  still available)

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Fusion by helium-capture (alpha-particles )
burns C, O, Ne, Mg, Si ..
REMINDER layers of onion

• Helium nucleus (2 protons) is absorbed, energy is
  released
• Elements are created going up periodic table in
  steps of 2

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Onion-shell fusion burning stops with IRON
(Fe, 26 protons )
CARTOON
FISSION
FUSION
Iron does NOT release energy when it fuses !
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REMINDER
Several fates for massive star
1. Strong winds shrink star, may end as WHITE
DWARF 2. Or core burns to Fe, eventually sudden
CORE COLLAPSE ! SUPERNOVA
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Core collapse (massive star) SUPERNOVA

• Rapid disassembly
• of elements in core
• neutrons
• neutrinos

• Neutron degeneracy
• pressure stiffens
• collapsing core ---
• push of neutrinos
• envelope bounces !
• SHELL BLOWS OFF

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Only supernova explosion creates elements
heavier than iron magic of nucleosynthesis
SN shells, and what is left at center ?
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Core Collapse SUPERNOVA

• Exploding remnant of massive star disperses
  heavy elements through the galaxy
• Inside may be a neutron star a remnant core of
  pure neutrons!

Crab Nebula (M1), first seen as SUPERNOVA on 4
July 1054 from China -- visible in daytime
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SNR Crab Nebula M1 4 July 1054
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Crab SNR composite Oct 06 Spitzer (IR), Chandra
(X), Hubble (V)
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Observing Supernovae

• About 1 per century per galaxy (none in Milky Way
  since 1604 Kepler) 1572 Brahe 1054 Crab
  1004 brightest
• Bright explosion visible for weeks/months - some
  visible in daytime!
• Remnant visible for 10,000 years as huge bubbles
  and veils longer in radio

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Was Crab SN recorded in Chaco? .and nothing
recorded in Europe!

• Petroglyph from Chaco Canyon
• Correct position relative to new moon for Crab
  Supernova, but some doubt
• Check this on your SkyGazer software

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Clicker review red giants

• The main source of energy for a star as it grows
  in size to become a red giant is _______ .
• A. gravitational contraction
• B. hydrogen fusion in a shell around core
• C. helium fusion in the core
• D. hydrogen fusion in the core

B.
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Neutron stars
More massive, smaller in size!
Star with a crystal crust ! Idea of neutron
stars first suggested in 1930s (Landau, Zwicki,
Baade, Oppenheimer) but seemed like wild
dreaming
.
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Favorite Postcard Size of Neutron Stars

• Structure determined by gravity vs. neutron
  degeneracy pressure
• Size 10 km. More massive, smaller !!
• Crushing gravity at its surface, so not a nice
  neighbor or place to visit . as tourist try
  Big Apple instead.

BRONX
MAN
QUEENS
BROOKLYN
STATEN ISLAND
Neutron star over NYC !
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Observing theFirst Pulsar BIG discovery
1.3 sec period

• Jocelyn Bell Cambridge (UK) graduate student in
  1967 ( Anthony Hewish) discovered pulsars by
  accident
• Little Green Men (LGM) ? Just WHAT could cause
  signal?

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Pulsar rotating neutron star
Fierce magnetic fields sizzling electrons
fast rotation ? finest lighthouse
Thomas Gold 1968
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Pulsars and Neutron Stars
Pulsars are lighthouses in our Galaxy!
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Why pulsars spin so fastVast shrinking
conserves angular momentum

• Collapse to a neutron star increases both
  rotation and magnetic fields
• Newly collapsed neutron stars can rotate hundreds
  to thousands of times per second !

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Mystery resolved when pulsar discovered in Crab
Nebula (known to be supernova remnant) --
Messier 1 or M1 !
The Crab pulsar also pulses in visual light
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Spinning Bowling Ball Demo Neutron Star in the
Lab Sound on the Web
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REMINDER
Pulsar rotating neutron star
Fierce magnetic fields sizzling electrons
fast rotation ? finest lighthouse
SYNCHROTRON RADIATION
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Synchrotron radiation
beaming from neutron star and many other
energetic places (quasars)
scream from electrons spiralling along
magnetic fields like in particle accelerators
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Synchrotron Radiation

• Fast electrons in strong magnetic fields ?
  neutron stars, black holes
• Different shape from thermal radiation emits at
  all wavelengths, strongest in radio

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Visible vs. X-ray emission
Visible light

• Thermal light from stars ? visible and IR
• Synchrotron light from neutron stars ? X-ray and
  radio

X-ray light
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Visible Light vs. Radio Thermal vs. Synchrotron
Same galaxy -- radio
Elliptical galaxy -- visible
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Back to famous friend !
SN Crab Nebula M1 4 July 1054
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Crabs pulse patterns
x-ray
visible
radio
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Crab Nebula SNR
optical
infrared
x-ray
radio
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Chandra X-ray view of Crab center
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Crab pulsar at work Nov 00 Apr 01

Chandra X-ray
HST Visible
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Gradual slowing down of pulsar rotation
Energy emitted in pulses comes from
rotational kinetic energy
(Listen to pulsars from our website)