Supernova!

1
Supernova!

• The fate of stars with mass greater than 9 solar
  masses.
• Principally O and B stars.

2
The context

• Stars like the Sun (Mlt9 Msolar) recycle about 50
  of their mass back into the ISM through Planetary
  Nebula leaving behind a White Dwarf as a stellar
  remnant.
• Stars more massive (O and B main sequence stars)
  recycle 95 of their mass back into the ISM
  through an event called a super nova (super
  star).

3
The Event

• Sun-like stars (Mlt 9 Msolar) stop producing
  energy with Shell Helium Burning and leave behind
  a carbon core (White Dwarf).
• Stars more massive continue to fuse heavier
  elements in their cores as they evolve.
• Carbon burning at 600 Million K
• Neon burning at 1.2 Billion K
• Oxygen Burning at 1.5 Billion K
• Silicon Burning at 3 Billion K

4
The Event

• Finally an Iron core with a mass of about 2 solar
  masses and a radius of 500 kilometers develops.
• At this stage, the stars envelope has swelled to
  5 AU (Supergiant).
• The iron core is so dense that its own gravity
  causes it to collapse on itself.

5
Collapse of the Iron Core

• Iron atoms are reduced to individual protons,
  neutrons and electrons in a fraction of a second.
• Collapse continues and individual protons and
  electrons are squeezed together to form neutrons
  and neutrinos.
• In immense flood of neutrinos attempts to leave
  the core but cannot escape the incredible dense
  matter in the core and they exert an outward
  pressure on the star.

6
Core Rebound

• The collapsing core of neutrons reaches nuclear
  density and stiffens.
• The sudden onset of stiffening causes the
  collapsing core to rebound and bounce out to meet
  the infalling envelope.
• The combined effect of the rebounding core and
  the pressure from neutrinos propels the inner
  layers of the star outward at near light speed
  velocities.

7
A Supernova is formed!
8
The Implications

• The remains of the star are NOT recycled back
  into the ISM but remain as a neutron star or a
  black hole.
• These stellar remnants do not emit radiation and
  are essentially the end of the line for these
  high mass stars.
• Within the exploding envelope of the star fusion
  occurs creating new heavy elements.

9
We are Children of the Stars

• The new heavy elements are dispersed into the ISM
  and will later be part of a new star forming
  system.
• All elements in the ISM heavier than hydrogen are
  created by these supernova.
• Oxygen in the water of our bodies
• Carbon in the proteins of our cellular chemistry
• Calcium in our bones and teeth
• Iron in our hemoglobin
• Silicon in the very rocks we walk on

10
Recall the Aristotelian View of the Universe.

• The Heavens were a spiritual place that
  represented the ultimate source and destination
  of mankind.
• In the modern scientific view, the stars are the
  physical source of the material that we are made
  of, and as the Sun evolves, our ashes will be
  sent back into the ISM.

It is understandable that some people have
replaced a faith-based religious view with a
scientifically-based worldview. The parallels
are clear.
11
The Standard Candle Concept

• Any astronomical object with a known luminosity
  is considered a standard candle.
• When a standard candle is observed its distance
  can be determined from the difference between
  its apparent magnitude and its known absolute
  magnitude (m-M).

12
The Standard Candle Concept
The Standard Candle Concept

• Supernovas are good standard candles because
• They have a uniform peak absolute magnitude, and
• They are VERY luminous.
• The absolute magnitude of a supernova is
• M-17

13
How luminous is a Supernova?

• Note that the full Moon has an apparent magnitude
  of about 12 and that it can cast shadows.
• A supernova at a distance of 10 parsecs (32 light
  years) would appear to be 100 times brighter than
  the full Moon!
• It would cast shadows on the Earth from this
  distance!

14
How bright would a supernova be at various
distances?

• At 10 parsecs, m -17
• At 100 parsecs, m -12
• At 1000 parsecs, m -7
• At 10,000 parsecs, m -2
• At 100,000 parsecs, m 3
• At 1,000,000 parsecs, m 8

15
With the Hubble Space Telescope that can see to
m28, a supernova can be seen to a distance of 10
billion parsecs!

• Supernova are so luminous that they are useful
  standard candles for exploring the distant (and
  early) universe.

16
What you need to know about Supernovas for the
exam

• What types of main sequence stars will eventually
  supernova? What types do not?
• What is the interior of the star like just before
  the Supernova event?
• How are supernovas important for the chemical
  evolution of the Universe?
• What do astronomers use supernova for?