Transcript Recap: High Mass Stars

Life Cycle of Stars
• 1st Step:
–Stars form from nebulas
• Regions of concentrated dust and gas
left from the BIG BANG (or other
stars’ demise)
–Gas and dust begin to collide,
contract and heat up
• All due to gravity, even the smallest
particle has gravitational attraction!
–[What 2 things affect gravity?]
Eagle Nebula
Orion Nebula
Horsehead
Nebula
Triangulum
Nebula
• 2nd Step:
– As nebula contracts, a small star is formed
• Called a protostar
– Eventually, the protostar will begin nuclear FUSION
• Hydrogen protons attract to each other
– Strong nuclear force (Nucleus particles stick)
» Heat (15,000,000° C) + gravity and…..
\FUSION begins
• Continued FUSION is necessary for stars to survive.
• Can take 30,000,000 years for protostar to form
• 3rd Step: The HertzsprungRussell Diagram
– Star joins the main sequence
• 90% of stars spend life here
• Nuclear fusion = Hydrogen into
Helium
• Mass of star determines location on
main sequence
• Ranges in size from ½ Sun to 20
times the Sun’s size
• Color depends on the surface
temperature
• Beginning of the End:
– Stars begin to die when they run out of
hydrogen
• Gravity begins to take over
Really Low Mass Star
• Doesn’t burn Hydrogen (dud) 
• Begins to cool and forms a Brown Dwarf
Low Mass Stars
• From ½ all the way down to 0.075% of the
Sun’s mass
• Burn cool, less than 3500 K. Dim light.
• Can live a REALLY long time.
10,000,000,000,000 years?
• Our nearest star neighbor is Proxima
Centauri, a red dwarf.
• Most numerous stars in the entire Universe!
Intermediate mass Stars (like the
Sun up to 5x Sun)
– Star core begins to shrink; outer core of
hydrogen begins to fuse and expand
• Star gets bigger
Red Giant!
Eventually the outer shell is blown off (planetary
nebula) and the remaining core is a white, hot and
small…
White Dwarf!
High Mass Stars—form
supergiants!
Supergiant
Red Giant
S
S
• Core is no longer fusing (iron is it!)
• The balance of pressure loses and the entire
star collapses
• Massive explosion
– Creates heavier elements
Supernova!
Neutron Star
• Star with a core from 1.4 to 3 times the size
of the Sun becomes a neutron.
• Electrons and neutrons combine into
neutrons.
• 10 km (6 mi) in diameter with a mass more
than our Sun!
• A teaspoon of neutron star would be about
10 million tons
• Acts like a huge magnet with magnetic
poles, can be a pulsar
What is a Black Hole???
– An object so massive and dense that not
even lightBlack
can escape
its
gravity
Holes Info Sheet
– The end result from a supernova that
leaves a core of 3+ times the Sun.
– Collapses to a singularity
• Recap: Death of Stars: Low and Medium
Mass
Main Sequence Star
Red
Dwarf
Red Giant
Planetary Nebula
White Dwarf
Black Dwarf
• Death of Stars: High Mass
Main Sequence
Star
Red Super Giant
Supernova
Neutron Star
Black Hole
• Recap: High Mass Stars:
– Core size greater than 1.4x our sun
• Create high mass elements such as iron
– Neutron Star
• Formed if remaining star is 1.4-3x sun’s mass.
– Black Holes
• Formed if remaining star > 3x sun’s mass
Recap Video
• Death of Stars:
– What stars end up as depend on mass
– Low and Medium mass stars
• Planetary nebula --------- white dwarf
– High mass stars
• Supernova --------- neutron star or black hole
• As fusion begins to slow down, the core of
the sun will contract
• Temperature in the core will rise
• The outer layers of the sun will expand,
consuming in the inner planets
• Sun will become a Red Giant
Video
Link
– Core of the sun will begin to fuse helium
into larger elements such as carbon and
oxygen
– Continuing over the next 100 million
years…
• Core will become entirely carbon and
oxygen
• Core will contract
• Outer layers will expand
– Outer layers will form a planetary nebula
• Core of sun will become a white dwarf
How did it start?
Gravity, gas pressure, magnetic
fields, and rotation cause disk to
form around protostar.
Conservation of angular momentum! 