High Mass Stars, Supernovas, and Black Holes

1
The Vela Remnant
2

• Life Stages of High-Mass Star
• Main Sequence H fuses to He in core
• Red Supergiant H fuses to He in shell around He
  core
• Helium Core Burning
• He fuses to C in core while H fuses to He in
  shell
• Multiple Shell Burning
• Many elements fuse in shells
• 5. Supernova leaves neutron star behind

Not to scale!
3
High-Mass Stars (M gt 9 M?)

• Massive stars zig-zag in HR Diagram

SUPERGIANTS
fuel used up
new nuclear fuel ignites
core of star shrinks, heats up
until last fuel is used up
4
The End for a Massive Star
onion skin structure in core
iron core gets too massive and collapses
BUT heat CANNOT be released by nuclear reactions
using iron
5
Thought Question

• How high will the small superball bounce when I
  drop the stack of 4 superballs from 1 foot above
  the ground?
• It wont bounce it will come to a dead stop.
• It will bounce back to its start (2 feet).
• It will bounce twice as high (4 feet).
• It will bounce 4 times as high (8 feet).
• It will hit the ceiling.

6
Supernova Explosions

• Learn what happened by looking at
• expanding gas cloud
• energy release
• remaining star corpse

ABOUT 12 LIGHT-YEARS
7
The Crab Nebula (1054 A.D.)

• new star visible during DAYTIME for 23 days!
• visible at night for 653 days
• expanding gas cloud discovered much later
• about 6300 light-years away

ABOUT 12 LIGHT-YEARS
8
Simeis 147

• about 105 years old

150 LIGHT-YEARS
9
Tychos Supernova (1572 A.D.)

• about 7,500 light-years away
• (picture taken in X-rays /infrared /visible light)

ABOUT 24 LIGHT-YEARS
10
Keplers Supernova (1604 A.D.)

• about 13,000 light-years away
• (picture taken in X-rays)

11
The Crab Nebula (1054 A.D.)
? pictures taken in 1977 and 2001
ABOUT 12 LIGHT-YEARS
12
Expansion Time
13
Energy Release

• explosion can outshine much of a galaxy
• how much energy is released?
• what can release so much energy in a short time?

SUPERNOVA
14
Where Does the Energy Go?

• Light add up energy collected during explosion
• Gas kinetic energy
• Neutrinos electrons, protons combine to form
  neutrons and

15
Where Does Energy Come From?

• Fusion? For H fusion over stars whole life
• Gravitational potential energy

16
Low-Mass Star Corpses White Dwarfs
neutron star
.

• about same size as Earth, but higher mass white
  dwarfs are smaller
• cant be more massive than 1.4 M? or collapse!

17
High-Mass Star Corpses

• even when we know where to look, corpse is hard
  to find
• something so small its luminosity is tiny?

18
Massive Star Corpses

• After all fuels run out at center
• iron core collapses
• forms tiny neutron star
• (protons, electrons crushed together to make
  neutrons)
• collapsing gas bounces off

CITY SIZE!!!
19
Thought Question

• If a white dwarf is about 600 times larger (in
  radius) than a neutron star but has the same
  mass, how does the neutron stars density compare
  to the white dwarfs?
• about 600 times lower
• about (600)2 times lower
• about (600)3 times lower
• about 600 times higher
• about (600)2 times higher
• about (600)3 times higher

.
6000 km
10 km
20
Angular Momentum
The larger the angular momentum, the harder it is
to stop its spinning or revolving

• Angular momentum depends on
• mass of object
• speed of rotation or revolution (perpendicular to
  line from center to object)
• distance from center of motion

CONSERVATION OF ANGULAR MOMENTUM amount of
angular momentum does not change unless a
twisting force acts on the object
21
Rotation
CONSERVATION OF ANGULAR MOMENTUM
22
Pulsars
23
Star Chemistry

• explosion spreads chemicals into space
• Type II supernova (massive star)
• mostly H, some heavier elements
• Type I supernova (white dwarf in binary)
• mostly iron
• ? new generations of stars form from enriched gas

24
Thought Question

• Supernova explosions spread heavy elements like
  iron into space. If you find a star that has a
  smaller abundance of iron than the Sun, it is
• probably younger than the Sun.
• probably older than the Sun.
• not possible to tell the stars age

25
You are Star Stuff

• Dying stars give chemicals back
• supernova explosions (main source of Fe)
• planetary nebulas (source of C, N, O)

LOW-MASS STAR DEATH
STAR FORMATION
HIGH-MASS STAR DEATH
POLLUTION OF GAS CLOUDS