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
Brown Dwarf going around a Red Dwarf
Low
Mass
4.2 light
years Stars
away!
• 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!
The smallest of the red dwarves would be about ten
times less massive than our sun. If it were OUR sun,
it would only be about 8 times brighter than a full
moon..
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!
Red Giant Mira (about 332-402
times the radius of our Sun)
Eventually the outer shell is blown off (planetary
nebula) and the remaining core is a white, hot and
small…
White Dwarf!
M
Helix Nebula
High Mass Stars—form
supergiants!
Hydrogen burning 7
million years
Helium burning 500
thousand years
Carbon burning 600
years
Neon burning 1 year
Oxygen burning 6
months
Silicon burning 1 day
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
Low Mass
Main Sequence Star
Medium Mass
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 the inner planets
• Sun will become a Red Giant
Click
ME!
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! 