Stellar Evolution
Lecture 18
PH 1040: Astronomy
Shane L. Larson
Weber State University
1
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Stellar Evolution Lecture: From Stellar Nurseries to White Dwarfs, Study notes of Physics
An in-depth exploration of stellar evolution, covering topics such as stellar nurseries, stellar ignition, stellar energy sources, and the various stages of a star's life off the main sequence, including red giants, planetary nebulae, and white dwarfs. Students will gain a comprehensive understanding of the processes that shape stars and their eventual fates.
Typology: Study notes
Pre 2010
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Stellar Evolution
Lecture 18 PH 1040: Astronomy Shane L. Larson Weber State University
- Homework: Due Friday
- Mon, Mar 3: Review Day
- Wed, Mar 5: Midterm Handed out
- Fri, Mar 7: In class activity (day before Spring Break)
Schedule
- Third quarter Moon; near Antares in early morning
- Jupiter just to left of Sagittarius
Sky This Week
- Stellar nurseries
- Nuclear processing
- HR Diagram
- Late life
Storyline
- Molecular clouds are the parents of the stars, and often give birth to many stars, not just one
- Clusters of stars^ are born together (like Pleiades)
- As stars are born, their light and stellar winds blow out surrounding nebula, making it luminous
Stellar Nurseries
- Molecular clouds are the parents of the stars, and often give birth to many stars, not just one
- Clusters of stars^ are born together (like Pleiades)
- As stars are born, their light and stellar winds blow out surrounding nebula, making it luminous
Stellar Nurseries
M42 (Orion Nebula)
- The brightest nebula in the sky is a stellar nursery!
- Looking in the core of the nebula, we see young stars blowing holes in the nebula!
- Astronomical observations have yielded enough 3D information we can fly through the nebula!
M42 (Orion Nebula)
- The brightest nebula in the sky is a stellar nursery!
- Looking in the core of the nebula, we see young stars blowing holes in the nebula!
- Astronomical observations have yielded enough 3D information we can fly through the nebula!
Protoplanetary Disks
- As the star forms from the collapse, anything that doesn’t become part of the star flattens into a slowly rotating disk
- Planets will form from this disk
- When the star “turns on”, it clears an area around it
- First discovered disk was Beta Pictoris
- Stellar energy results from thermonuclear fusion, first described by Hans Bethe
- Stellar fusion process is called the proton-proton (pp) chain: - p + p^ =^ Deuterium^ (pn) - Deuterium + p^ =^ He^3 (ppn) - He3 + He3^ =^ Helium^ (ppnn)
- Overall, 6 protons become 2 free protons, and 2 protons with 2 neutrons in a Helium atom
Stellar Energy
- Second process (also proposed by Bethe) called the Carbon-Nitrogen- Oxygen (CNO) cycle - Just like the pp-chain, this converts hydrogen to helium in stars (and produces energy)
- Overall, 4 protons end up being converted into a single helium nucleus
- Most important in stars more massive than the Sun
Stellar Energy
Life on the HR Diagram
- Star burns up its hydrogen, leaving behind helium “ash”
- Burning happens in core, and counteracts gravity