Stellar Evolution

NGC 3603 Bok globules and giant gaseous pillars (evidence of embryonic stars), circumstellar disks around young stars progressing to aging, massive stars in a young starburst cluster blue super-giant with its ring and bipolar outflow marks the end of the life cycle.

STAGE ONE u Stars begin as a NEBULA - a dark cloud of gas and dust u Made mostly of hydrogen and helium with small amounts of heavier elements Eagle Nebula M16

Horse Head Nebula

Veil NebulaTrifid Nebula

Thackeray's Globules in IC 2944

Omega or Swan Nebula

Ghost Head Nebula

u The nebula begins to contract and gravitational attraction increases u It continues shrinking and starts to spin. u Eventually it forms a flat disk with a PROTOSTAR in the middle

Planetary Disks Forming

STAGE TWO - Main Sequence u Longest part u Energy is produced as fusion take place in the core of the star u The energy from fusion balances the force of gravity and makes it a very stable stage

Stage Three u Happens when almost all of the hydrogen atoms have fused into helium atoms u The core contracts due to the force of gravity u This increases the temp and causes the helium to fuse into carbon u This gives off a lot of energy and the star swells up to a giant or supergiant star

Stage Four u Helium fusion ends u The star loses its outer gases and reveals a core u An expanding shell of gases shed by this dying star forms a PLANETARY NEBULA

Ant Nebula

Helix Nebula

Stingray nebula (Hen-1357), the youngest known planetary nebula.

The "Spirograph" Nebula

Cat’s Eye Nebula

u The star collapses inward and forms a hot dense core of matter called a WHITE DWARF u Some white dwarfs may explode into a NOVA while they are cooling

What about really BIG stars?? u Stars with masses times greater than the sun can produce a huge explosion called a SUPERNOVA SN1987A

What happens after the explosion? u The core may contract into a very small, dense ball of neutrons called a NEUTRON STAR – u If it rotates it is called a PULSAR

u Really large stars contract with greater force and become a BLACK HOLE

Centaurus A (Hidden Black Hole)

Classifying Stars Hertzsprung-Russell (HR) Diagram Plots temp. v. luminosity Most stars are main sequence