1. The Star Lifecycle

2. The Beginnings
The development of a star begins with the nebula, a swirling cloud of interstellar gas and dust molecules
Because of gravitational attraction, dense parts of the nebula become more dense. These high density areas can unite into a tightly packed object called a protostar
Gravitational collapse
(in between stars)

3. Eagle Nebula – 95 light years across

4. The pillars of creation – in eagle nebula (towers are over 4 light years tall). About 7000 light years from earth.

6. Protostar
As the protostar collects more material and becomes denser the temperature and pressure of it’s core increases.
When the inner temperature reaches ~ 10 million degrees Celsius, a nuclear reaction ensues
The fusion of Hydrogen atoms into an atom of Helium

7. Star Continued
The fusion of H into He releases a vast amount of energy. This energy is radiated in many forms (visible light and heat!)
This fusion causes the accretion process to stop, and the accretion disk will coalesce into planets
(adding of material)

8. The bright spot is a new star igniting

9. Main Sequence Star
The newly formed star will “burn” hydrogen for billions of years
Our sun is in this phase (our sun is 4.5 billion years old, about halfway through its main sequence)

10. Balancing act
The incredible weight of all the gas and gravity try to collapse the star on its core.
As long as there is a nuclear reaction taking place, the internal forces will balance the external gravitational forces.

12. Red Giant
When a star is low on hydrogen, fusion slows, and the stars core begins to collapse
The collapse causes the core to heat up, eventually reaching a temperature hot enough to start fusing He atoms together into Carbon.
Increased temp causes increased fusion rates, thus the outer layers will experience more pressure and GREATLY expand as a result
Luminosity 10000x

13. 1 AU = 150 million km

14. Death of Stars Like the Sun
When the He fuel runs out the core begins to collapse, and increase in temperature, causing the fusion of some heavier elements.
Star has expanded so much that it doesn’t have the gravity to hold it’s outer layers – becomes planetary nebula
The core expands and cools, no longer undergoing fusion (but is still extremely hot). It glows white
white dwarf.

15. 97% of stars in the Milky Way will “die” in this manner
The White Dwarf will eventually cool down to the temperature of the surrounding space
Black dwarf

16. Death of a Massive Star
When He runs out the star begins to fuse heavier elements
The heavier the element the less energy produced.
Iron is the heaviest element that produces energy

17. Supernova
Once the core becomes iron, the star has no more fuel, and can no longer support it’s own weight, thus collapsing on itself
The core becomes so tightly packed that protons and electrons merge to form neutrons.
The outer layers of the star fall inward on the neutron core, thereby crushing it further.
In less than a second, the iron core, which is about the size of the Earth, shrinks to a neutron core with a radius of about 6 miles (10 kilometers).

18. Supernova
The core heats to billions of degrees and explodes (supernova), thereby releasing large amounts of energy and material into space.
The energy of the collapse and explosion is great enough to cause fusion of heavier elements! (Heavier then Iron)

20. Aftermath
The remains of the core can form a neutron star or a black hole depending upon the mass of the original star.
Neutron stars are the densest and smallest stars known to exist in the universe; with a radius of only about 10–13 km, they can have a mass of two Suns! (there is no more fusion)

21. Neutron Stars

22. %

26. Black Hole
With some SUPER massive stars the gravitational force can be so high that the core of the star can collapse into a singularity, a point of near infinite mass and gravity, known as a black hole
The gravity surrounding a black hole is so great that light can’t even escape! (how we know they exist) – why its called black hole