Stellar Life Cycle

Bell Ringer – match term with definition

1. Large cloud of gas and dust

2. Longest stage

3. Hydrogen is depleted and outer layers expand and cool

4. Extremely dense

5. Light cannot escape

A. Black hole

B. Giant

C. Main sequence

D. Nebula

E. Neutron star

Bell Ringer

1. Describe how stars release energy.

2. Outline the past and future of our Sun.

Nebula

• Cloud of gas and dust• 70% hydrogen, 28% helium, 2%

other elements• Weak gravitational attraction

Nebula – cloud of gas and dust. Birthplace of stars.

NGC 604 – one of the largest regions of star birth currently known.

Contains massive stars, about 120 times larger than our sun.

Orion Nebula – Closest region of star formation to earth

Eagle Nebula – pillars of star-forming gas

Nebula to a star• Force (i.e. explosion from nearby star)

compresses particles• Nebula begins to contract• Particles come closer together• Temperatures increase• At 10 million K, nuclear fusion begins• Star is born

Nuclear Fusion

http://www.youtube.com/watch?v=-gRagBg7mjM&NR=1

Main sequence star

• Energy is generated in the core of the star• Hydrogen atoms fuse to helium

atoms• Longest stage in life of a star• Balances pressure from fusion

heat with gravity

Our closest star

Giants and Supergiants• Hydrogen fuel is used up• The core of the star contracts, increasing the

temperature• Outer shell of star expands and cools • Helium fuses to form carbon

• Giants are 10 times bigger than the sun. • Supergiants are 100 times bigger than the

sun.

Red giant at the center, illuminating a cloud of gas

Betelgeuse – Red Supergiant

Planetary Nebula

• Helium fusion ends• Star loses its outer gases• The core heats and illuminates

the ring of gas

Planetary Nebula – glowing shell of gas and plasma formed by some

stars when they die

Planetary Nebula

White Dwarfs• Gravity pulls the last matter of

the star inward• Hot, dense core of matter• Shine for billions of years before they cool

completely into a black dwarf.

Nova

• During process of white dwarf cooling, explosions may occur

• Release energy, gas, and dust into space

• Star becomes much brighter and then fades back to its normal brightness

• May occur several times

Nova – large explosion of a white dwarf star. Energy, gas, and dust

are released into space.

Supernova• Occur in very large stars

• Large stars contract producing very high pressures and temperatures

• Carbon fuses into magnesium which then fuses into iron

• The iron core absorbs huge amounts of energy and collapses, causing the outer part of the star to explode

Supernova – large star explosion

Neutron Stars

• The core of a supernova contracts into a very small, dense ball of neutrons

• Rotate very rapidly• Some emit beams of radiation

and are called pulsars

Pulsar - highly magnetized, rotating neutron stars that emit beams of

electromagnetic radiation

Crab Pulsar

Black Holes

• After a supernova,

some large stars

contract with even greater force

• The force crushes the core of the star, leaving a hole in space

• The gravity is so great that not even light can escape from it

Recycling

• Matter emitted by a star over its life time is recycled and can become part of a new nebula

Supernova remnant – ejected material expanding from the star explosion

Stellar Evolutionary Stages