red giant phase to remnant (chapter 10). student learning objective describe or diagram the...
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Red Giant Phase to Remnant(Chapter 10)
Student Learning Objective
• Describe or diagram the evolutionary phases from the beginning of stellar formation to remnant
Low Mass & High Mass
What happens during the red giant phase?
Nuclear fusion in the core stops.
All hydrogen has been usedIt is not hot enough to fuse helium
The core and surrounding layers collapse.
Collapsing layers heat
Gravity “wins”
Inert Helium Core
Hydrogen begins burning in a heated shell surrounding the core.
Outer layers expand and cool.
Pressure “wins”
Practice
1) What provides “normal” pressure in a star?
2) Why do collapsing layers heat?
3) Why do the outer layers cool?
Helium Fusion in Core
+
Hydrogen Fusion in Shell
=
Outer Layers Expand More
Helium fusion begins in the core.
T = 100 Million Kelvin Helium Fusion = Carbon
and Oxygen core
Science Daily
1-3 Msun
Low Mass Star
High Mass Star
Low Mass High Mass
RR Lyrae variables Cepheid variablesPeriod = less than 1 day Period = 1-50 days
The Red Giant pulsates.
Hydrostatic equilibrium is out of balance.
Practice
1) Describe what is happening as a Red Giant pulsates.
2) What will happen to Earth as the surface of the Sun approaches?
Diameter 100+ larger
Mercury and Venus in Sun
Earth at surface of Sun
What remains of a Low Mass Starafter nuclear fusion ends?
Stars less than 0.4 Msun become a Red Dwarf.
Extremely low mass stars can only transport heat by convection.
Star accesses hydrogen from all layersFusion ends when all hydrogen is goneRemnant slowly fades
A Red Dwarf with an Earth
NASA
Low mass stars like the Sun become a White Dwarf.
Hot collapsed core (White Dwarf)Surrounding ejected layers (Planetary Nebula)
White Dwarf
The Process of becoming
a White Dwarf
• Core contracts
• Outer layers expand and thin
• Pulsating star ejects outer layers (Planetary Nebula)
• Planetary nebula glows (heat excites gasses)
The White Dwarf will fade over time into a Black Dwarf.
A White Dwarf is the compact core remnant of a low mass star.
The Process of becominga White Dwarf
Electron Degenerate Matter
Ends core collapse of Low Mass star
Electron orbits are restricted
Orbits “hold up” the White Dwarf core remnant
Planetary nebula in constellation Lyra
Ring Nebula
The Littlest Ghost Nebula
Image Credit: APOD
White Dwarf Limit
The Chandrasekhar limit is 1.4 Msun.
A “Sun” becomes the size of Earth As much as 40% of star ejected
What remains of a High Mass Starafter nuclear fusion ends?
A high mass star goes through several “Red Giant” phases as it fuses heavier nuclei in the core and surrounding layers.
Then it explodes! (SN Explosion)
Image Credit: Australia Telescope National Facility
Type II SupernovaHigh mass stars explode.
Energy production ends abruptlyCore cannot fuse iron (Fe)Degenerate pressure cannot stop collapse
Gravity “wins”
The Explosion
A Type II SN explosion only takes milliseconds.
Core collapses Entire star falls in on itself and reboundsA pressure wave (shock wave) is producedOuter layers are blasted into space1028 Megatons of TNT releasedHeaviest elements are produced100’s to Millions times brighter than original star
Boom!
Type II Supernova
Neutron Star or Black Hole
In 1 year 0.3 LY acrossIn 100 years Several LY across
SN Remnant
The outer layers of the high mass star expand rapidly and collide with ISM.
ISM glowsMay initiate new Star formation
The Crab Nebula from VLT
Supernova Remnant Cassiopeia A (Hubble)
Kepler’s Supernova Remnant
NASA
What are the possible fates in a binary system?
Each of the stars in a binary system gravitationally controls a volume of space called a Roche lobe.
Matter at the inner Lagrangian point, can transfer to a companion object.
The object accreting matter may go nova!
Nova
A Nova is a thermal nuclear explosion on the surface of a core remnant.
Red Giant fills Roche LobeCore remnant companion
accumulates matterNova Nova Velorum 1999 (APOD)
Type Ia SN
A Type Ia Supernova is a Nova that destroys the object accreting matter.
Object accumulates too much massExplosion of entire object (Type Ia SN)Nothing remains
Practice
1) What is the primary difference between a Nova and a Type Ia SN?
2) Can our Sun become a Type II SN? Why?
3) Can our Sun become a Nova? Why?
4) Can our Sun become a Type Ia SN? Why?
Why are star clusters important?
The HR diagram can show the age of the cluster.
Comparing relative ages leads to understanding stellar evolution.
Open ClustersOpen clusters contain
young stars.
100 to 1000 membersSee individual stars25 parsecs across
Globular Clusters
Globular Clusters contain old stars.
Millions of membersAppears as single object10-30 parsecs across
Star clusters demonstrate the evolutionary process of stars.
PracticeWhich HR diagram shows the youngest cluster?