Main sequence Powered by Hydrogen Fusion Inside the

Main sequence Powered by Hydrogen Fusion: Inside the sun, 4 Hydrogen nuclei fuse to form 1 Helium nucleus, releasing light, heat and radiation.

Two Opposing Forces Pressure from Nuclear Reactions pushing outward Gravity pulling inward

Hertzsprung - Russell Diagram Main Sequence Stars Main sequence stars are “hydrogen-burners”. Going up to the left, stars get bigger and brighter and hotter, going from red hot to yellow hot to white hot to blue hot.

The mass of a star determines its fate 0. 4 – 8 M☉ Stars Brown Dwarf Tiny Stars Red Giant 8. 0 - 25 M☉ Stars White Dwarf Supergiant 25 – 100 M☉ Stars Supergiant Neutron Star Supernova Black Hole

The mass of a star determines its fate: 1. The smallest stars (0. 08 – 0. 5 M☉) start out as red dwarf main sequence hydrogen burners, then become hotter, brighter stars called white dwarfs when they collapse and reheat to “burn” helium.

Evolution of sun-sized stars 2. Medium-sized (0. 5 – 8 M☉) stars such as our Sun burn very slowly. Our sun will burn for another 5 - 6 billion years, mostly as a yellow dwarf main-sequence hydrogen-burner, then collapse under the force of gravity.

Evolution of sun-sized stars 3 a. This collapse will heat the outer layers of the sun, which will boil away into space, causing the sun to swell up into a red giant 400 X the diameter of the sun.

Evolution of sun-sized stars 3 b. This blazing fireball will engulf the 4 inner planets of the solar system, turning them to burnt cinders, with vaporized oceans and incinerated forests.

Red Giant vs. earth Final Score Red Giant - 1 Earth - 0

Inside a Red Giant 1) Helium fuses to form Carbon and Oxygen at the Core 2) Extra heat causes outer shell of hydrogen to fuse into He and billow out into space

Red Giants Vs. yellow dwarfs Arcturus 1. 1 M☉ 25. 7 R☉ Sun – Yellow Dwarf Main Sequence Sirius – Large Main Sequence Star

Evolution of sun-sized stars 4 a. After the red giant has finished blowing off its outer shell, a small, dense, very hot star called a white dwarf is left behind.

Sun vs. white dwarf 4 b. A white dwarf is the size of Earth, but has as much mass as the Sun…

Sun vs. white dwarf 4. A white dwarf the size of Earth, but as much mass as the Sun…

Stars grow and shrink… • Core begins runs out of H - Pressure drops. • Gravity becomes greater than pressure. • Core starts to shrinks to Earth-sized.

Stars grow and shrink… • Core temp rises and He fuses to make Carbon.

Stars grow and shrink… 4 c. The core of the white dwarf is held up by electron degeneracy pressure: the atoms are packed so tightly that their electron clouds are touching!!

Stars grow and shrink… • Pressure increases Atoms’ electron clouds are touching a white dwarf is formed!

White Dwarfs

Planetary Nebulae 5. The ballooning gases of the red giant will cool down to form a planetary nebula surrounding the white dwarf.

Planetary Nebulae These clouds form as the red giant’s outer shell expands and cools.

White Dwarfs White Dwarf at the center of a planetary nebula cloud

Evolution of sun-sized stars 6 a. When the white dwarf has used up all of its helium fuel, it will become a dark carbon cinder called a black dwarf – like a huge black diamond hiding in the night sky.

Evolution of sun-sized stars 6 b. (Our sun isn’t big enough to make the carbon core start any further fusion reactions. )

life cycle of a sun-sized star

Hertzsprung - Russell Diagram Main Sequence Stars White dwarfs are tiny but very hot (white hot - 10, 000 o K). The sun is medium sized and medium hot (yellow hot). Red Giants are very large but cool stars.

Core of Red Giant shrinks rapidly… Red Giant cools to form Planetary Nebula Red Giant – He-C reaction in core causes H to “flame out” at outer rim …to form a White Dwarf Main Sequence – Next 5 billion years

The Fate of Massive Stars

Evolution of massive stars Larger stars (8 – 25 M☉) burn brighter and die more quickly in violent cosmic spasms called supernovas.

Evolution of massive stars 1. When the H and He fuel is burned up, gravity takes over just as it did in the smaller stars.

Evolution of massive stars 2. This collapse causes temperatures to jump to 600 million K the star becomes a red supergiant.

Red super. Giant Betelgeuse in Orion 20 M☉ 1600. 0 L☉ 1200. 0 R☉ Maybe as big as 9. 0 AU – would swallow up Jupiter!!

Evolution of massive stars 3. Helium fuses to make many new elements (as large as Iron: Z = 26) in a process known as nuclear transmutation.

Layers of a Red-Supergiant…

…A Huge Element “Factory”

Evolution of massive stars 4. The iron core shuts down the nuclear reactions and the star collapses one final time…

Evolution of massive stars 5. This final collapse of the core creates incredibly high temperatures ( 8 billion K ) which trigger a huge thermonuclear blast – a supernova.

Shock Waves Spread Upward

Evolution of massive stars 6 a. When the star explodes, the blast sends star bits and shock waves all through the surrounding galaxies.

Supernova 1987 A

Supernova and Remnant Nebula After Before Supernova 1987 A

s 1987 A shock waves in 3 D

Evolution of massive stars 6 b. Elements of all shapes and sizes are formed and scattered as well. Supernova Remnant Cloud

Evolution of massive stars 7. In the core of the star, the pressure is so great that electrons are shoved into the nucleus…

Evolution of massive stars 7. …where they combine with protons to form neutrons!!

Evolution of massive stars 8 a. All that remains after a supernova blows up is a dense, spinning ball of neutrons called a neutron star…

Evolution of massive stars [ That mass that weighs 8 X more than the sun is now packed into a ball about 12 miles across. ] (shown here next to Manhattan)