Stellar Evolution

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Stellar Evolution	Stellar Evolution Topics H-R Diagram Stellar Evolution Nebulae Giants Blue Giants Hypergiants Red & Orange Giants Supergiants Dwarfs Supernova to Pulsar, Neutron Star, or Black Hole *Test* *Outline Page*
H-R Diagram Hertzsprung & Russell, in Early 1900s noticed that for most stars: The higher their temperatures, the brighter their absolute magnitudes. They graphed this data for a large number of stars. The result was what we now know as the H-R Diagram.
*STELLAR EVOLUTION*
	NASA Tutorial on *The Birth, Life and Death of Stars* (with lots of pictures - best with a broadband connection) Structure and Evolution of Stars, Cornell University Our Sun's evolution

Nebulae

Visit: The Web Nebulae
and find the star-forming nebulae.

1. Clouds of gas and dust,
2. 1,000s of light years across,
3. Gradually pulled together by gravity
4. Begins spinning during the same time
5. Pressures in center eventually increase temperatures
enough to start fusion
- around 10 million K

Go To Nebula Page

See a summarizing diagram from CSU Stanislaus
of the nebular hypothesis.

This Hubble picture of a portion of the Eagle Nebula, M16, shows many "stellar
nurseries"

Giants...
red to blue...
super giants, hypergiants, ....?

GIANTS Have different causes:

Blue Giants *- O class stars...*
	• Are stars that have started out far more massive than our sun - At least ten times larger • They burn much hotter - Therefore much brighter • They burn their fuel out much quicker than smaller stars
Hypergiants
	• Are 50, or even 100 times more massive than our sun. They will most likely appear to be blue.
	The Blue giants are found on the main sequence, but toward the top and on the left side, indicating they are very hot and very bright.
	What is the eventual fate of these very large stars? Supernova to Pulsar, Neutron Star, or Black Hole

Red and Orange Giants		A rough summary:
		Stars at the end of their "lives", relatively speaking: Whatever their original size:
	1.	They are just about burned out of their hydrogen fuel .
	2.	The center is occupied by helium that does not burn in a fusion reaction at these temperatures.
	3.	Temperatures in the center fall
	4.	Outward pressure, that had been great because of fusion, is decreased.
	5.	The star's mass begins to "fall in" on itself.
	6.	Rapidly, in stellar terms, the temperature then increases greatly in the helium center again.
	7.	The star's remaining hydrogen, surrounding the helium center, begins fusion at a greater rate than before
	8.	The energy from this non-central fusion is great, and causes the rest of the star to expand outward
	9.	The expanding star does not get any hotter at the surface, but the surface gets bigger, and the energy escaping the interior is hundreds of times greater than it was in its prime, so the star is very bright, and red
		- a red giant
	10.	At times - Helium fusion occurs if temperatures are hot enough, and it fuses to form carbon

Supergiants

• Are stars at the red giant stage that started out at least 10 times larger than our sun - probably as blue giants.

Dwarfs, White and Otherwise

White Dwarfs

• Formed when the collapsing core of a near-sun-sized star has burned even the helium.

• Continues to collapse,

• But does not have enough gravitational mass to keep the expanding "envelope"
of hydrogen (from when it was a red giant) from escaping out into space,
producing what we call a Planetary Nebula.

• Planetary Nebulae were misnamed, because when they were first discovered the resolution
of the telescopes of the time was not good enough to see what they were really like.
The Hubble Space Telescope has shown us these wonders, and many more, each
more amazing than the last:

The Original Planetary Nebula: The Ring Nebula, M57	Visit: The Web Nebulae and find planetary nebulae. Go To the Nebula Page.
*You may be able to see a white dwarf at the center of a planetary nebula.*

• These stars appear to just cool off until we can no longer see or detect them, their beautiful nebulae racing off into space.

Red Dwarfs	- M class
	Are stars at the lower right of the main sequence.
	Many of these stars are just barely large enough to become stars.
	They have the longest life spans of any stars. They may survive for 2 or 3 times longer than we expect that our sun will.

Take the Stellar Evolution Test

UPDATED: 03/03/08