Download Stellar Classification and Evolution What is a star? A cloud of gas

Stellar Classification and Evolution
What is a star?
 A cloud of gas and _________________________, mainly hydrogen and helium
 The core is so hot and dense that nuclear _______________________ can occur.
 The fusion converts light elements into ___________________ ones
Every star is different
 _________________________________:
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Tells us how much ____________________ is being produced in the core
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Can be calculated using __________________________________ and distance
 Color:

Tells us the surface ______________________________ of the star
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Determined by analyzing the _____________________ of starlight
 Mass:

Determines the life cycle of a star and how ______________ it will last
Measuring Temperature
 The temperature of a star is indicated by its ____________________
 Blue stars are _______________, and red stars are _________________
Star Classification
 Spectral Class
Oh Boy, A Failing Grade Kills Me

Determined by anazlyzing a star’s _______________________
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O stars are the _______________________ and __________________________
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M stars are the _______________________ and _________________________
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Our Sun is a _________ star
Hertzprung-Russell Diagram
 What information is plotted on the H-R Diagram?
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________________________________________________________
 What are the main stages of stars?

________________________________________________________
 Do stars always stay in the same stage?
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________________________________________________________
The Life of Stars
 Origins of stars
 Solar systems are created in giant molecular clouds of cosmic dust and ____________

When ____________________________ causes intense heat and pressure in the core of
the proto-star, it triggers _______________ and a star is “born
 Mass and Stellar Evolution
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The life cycle of a star is determined by its __________________
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More massive stars have greater gravity, and this ____________________ the rate of
fusion

O and B stars can consume all of their core hydrogen in a few _______________ years,
while stars with very low mass (red dwarfs) can take hundreds of __________________
of years.
 Brown Dwarf– a “Failed Star”

If a proto-star does not have enough ____________, gravity will not be strong enough
to compress and heat its core to the temperatures that trigger ___________________

If the mass is less than 0.08 x solar mass, it will form a Brown Dwarf (not actually a star)

Brown Dwarfs are _____________________________, but they do give off small
amounts of ___________ as they cool
 The Main Sequence

_________________________ life stage of a star
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Energy radiating away from star ________________________ gravitational pull inward
(hydrostatic equilibrium)
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Main-sequence stars fuse ______________________ into helium at a constant rate

Star maintains a stable size as long as there is ample supply of hydrogen atoms

The Sun will spend a total of ~10 billion years on the main sequence
 When hydrogen in the core starts to run low…
 In stars with masses more than 0.4 x solar mass, fusion slows down
 Outer layers of the star begin to ___________________ and surface temperatures fall
 The _______________ surrounding the core begins to fuse hydrogen
 Stars move out of the ___________ Sequence
 Red Giants and Supergiants
 _____________ stars
 ___________________ produced through shell fusion becomes part of the core
 Star’s core temperature _____________________ as the more massive core contracts
 The increased core temperature causes the helium left to fuse into ________________
atoms (triple-alpha process)
The “Death” of stars
 Depends on ____________
 “Low mass stars” are less than 8 solar masses
 “High mass stars” are greater than 8 solar masses
 The Death of Low-Mass Giants and Supergiants
 In _________ mass stars (0.4 – 8.0 x solar mass) strong solar winds and energy bursts
from helium fusion _____________ much of their mass
 The ejected material expands and cools, becoming a planetary ________________
(which actually has nothing to do with planets, but we didn’t know that in the 18th
century when Herschel coined the term)
 The core _____________________ to form a White Dwarf
 White Dwarf Stars
 The burned-out ____________ of a star less than 8 x solar mass becomes a white dwarf
 The carbon-oxygen core that remains is about the size of earth, but much more
_______________
 Theoretically, after all of the stored __________________ radiates out into space, these
stars will become giant crystals of carbon and Oxygen (Black Dwarfs)
 The Death of High-Mass Stars: Massive stars continue ___________________
 Massive stars (> 8 x solar mass) have more ___________________ than low-mass stars
 When helium fusion ends, gravity _____________________ the core and the
temperature rises beyond 600 million K
 Fusion of the atoms from __________________________ elements begins, and the star
becomes a luminous supergiant
 These stars produce neon, magnesium, oxygen, sulfur, silicon, phosphorous, and iron
 Supernova explosions
 The _______________-rich core signals the impending violent death of the massive star
 The core collapses in seconds, and the resulting temp. exceeds 5 billion K
 Intense ___________ breaks apart the atomic nuclei in the core, causing a shock wave
 After a few hours, the shockwave reaches the star’s ____________, blasting away the
outer layers in a _____________________________
 Supernova remnants are strong sources ______________ and _____________ waves
 Neutron Stars
 The ____________ left over after Supernovae can become Neutron Stars-- very small,
_______________ balls of NEUTRONS
 1 teaspoon of this would be approximately 1 billion tons on Earth
 Due to the great _________________ it rotates very rapidly, and some become
PULSARS
 Pulsars
 Rapidly-spinning neutron stars with very strong ______________________ fields.
 Jets of charged particles are ejected from the magnetic poles of the star.
 This material is accelerated, producing beams of _______________ in all wavelengths
from the magnetic poles.
 We can see this “lighthouse effect” many times per second
 Black Holes
 ____________________________ stars (>25 x solar mass) collapse into neutron stars
too massive to be stable
 They collapse in on themselves, forming a region of infinite density and zero volume– a
SINGULARITY at the center of a Black Hole
 Space “curves inward” and ________________ all matter and electromagnetic radiation