The Life and Death of Stars The Universe The Life and Death of Stars

WHAT IS A STAR? STAR: sphere of _______________________________________________ emits __________________________________________________ the sun is a _________________________________________________to Earth LIGHT-YEAR: distance that light travels in one year - about 9.5 trillion kilometers Earth is 8 light-minutes from the Sun

POWERING STARS WITH STAR FUEL NUCLEAR FUSION REACTIONS: the nuclei of _____________________________ (H) atoms combine into _____________________________ (He) atoms. When two particles fuse, __________________________ is released. Takes place in the ________________________________________ Core = extremely ________________, extremely ________________, and under extreme _________________________ (perfect for fusion)

At _________________in the core of the star, fusion ignites! NUCLEAR FUSION BASICS At _________________in the core of the star, fusion ignites! ______________________ atoms smash into each other --> ______________________ atom + particles + ____________ Where does the energy come from? Mass of four 1H atoms > Mass of one 4He atom Extra mass in converted to energy E = mc2 (Energy) = (mass) x (speed of light)2

OUR STAR – THE SUN Converts _________________________________of hydrogen to helium every second Converts 4.7 million tons of ____________________________________ every second We receive two billionths of that energy here on Earth - ____________________ Enough to power 100 light bulbs for 5 million years The sun formed about __________________________years ago. __________________________________________= size of the Sun Example: 3 solar masses = size of 3 Suns

Think! What is a star? (In your own words)? Why is our sun a ‘star’ and NOT a ‘planet’?

WE STUDY STARS BY STUDYING LIGHT Brightness of a Star Depends on the star’s _________________________________________________________ The brightest star in the night sky = ____________________________ (Because relatively close to Earth, 9 light years) Stars produce not only visible light but all types of __________________________________________________ Gamma Rays, X-rays, Ultraviolet, Infrared, Microwaves, and Radio waves. Scientists use special telescopes and satellites to see the different types of radiation coming from the stars

STUDYING STARS TEMPERATURE A star’s _____________ is related to its _________________ ____________________ objects glow with __________________ light that has ___________________________ wavelengths. that has ___________________________ wavelengths

The Hertzsprung- Russell Diagram (H-R Diagram) 1911: Danish astronomer Ejnar Hertzsprung compared and plotted magnitude of stars with their color (temperature) 1913: American astronomer Henry Norris Russell plots stars’ spectral class against magnitude

Together, the plots show a relationship between and . Shows that stars fall into .

Life Cycle of a Main Sequence and Massive Star STAGE 1 STAGE 2 STAGE 3 STAGE 4 STAGE 5 Main Sequence Star

STAR LIFE CYCLE: STAGE 1 – BIRTH MAIN SEQUENCE AND MASSIVE STARS All stars begin their life the same They form from a Stellar Nebula = Cloud of ____________________ at beginning of star life cycle Steps that lead to the birth of a star _______________________________________causes the gas and dust to accumulate (this is called accretion) A __________________________ forms (not yet a star) Temperature and pressure _______________________ until nuclear fusion begins (now a star) Nuclear fusion beginning means that a star has been born

STAR LIFE CYCLE: STAGE 2 – MIDDLE AGE MAIN SEQUENCE AND MASSIVE STARS Nuclear Fusion has begun and continues… Hydrogen fuses into helium and releases lots of energy The fusion reactions in the core of the star produce an _________________________________________that balances the _________________________________________due to gravity. Massive Stars = _____________________ fusion rates More gravity = hotter cores = uses hydrogen faster Over time, the percentage of the star’s core that is helium becomes __________________________. After millions of years, core will _______________________ of hydrogen and star will begin to die.

STAR LIFE CYCLES: STAGE 3 - DYING MAIN SEQUENCE STAR LIFE CYCLE As fusion slows, the outer layers of the star will _______________________ Becomes a red giant RED GIANT: 10 to 100 times larger Converts helium to _________________________ When the star _________________________of helium, fusion stops, outer layers will expand, and leave the star’s orbit. MASSIVE STAR LIFE CYCLE As fusion slows, the outer layers of the star will cool and expand Becomes a supergiant SUPERGIANT: ________________________ times larger Converts helium to carbon, oxygen, and… Has enough mass (gravity) so heavier elements can fuse into __________________

STAR LIFE CYCLES: STAGE 4 – DEATH MAIN SEQUENCE STAR LIFE CYCLE Fusion stops at helium Outer gas layers from red giant stage are released to form ______________________ PLANETARY NEBULA: Cloud of gas and dust at end of stars life cycle Sends enriched elements into space When the planetary nebula clears, a ________________ is left (part of Stage 5 for a Main Sequence Star) MASSIVE STAR LIFE CYCLE Supergiants can fuse heavier elements beyond helium Fusion stops at iron Develop layers of different elements with iron at the _____ Iron will not fuse Force of gravity becomes greater than force of fusion Eventually the core _________________________ and then explodes in a Type II supernova. SUPERNOVA: a gigantic explosion in which a massive star collapses and throws its outer layers into space

Layers of heavy elements in a supergiant

STAR LIFE CYCLES: STAGE 5 – AFTER DEATH MAIN SEQUENCE STAR LIFE CYCLE When planetary nebula clears, a white dwarf is left WHITE DWARF: a small, hot dim star that is the _______________________ of a main sequence star. Very dense - _______________________ Will cool until it becomes a black dwarf (no more light, big lump of coal) MASSIVE STAR LIFE CYCLE After a Type II supernova, either (A) ________________________ or (B) ___________________ forms. If the remaining core has a mass of __________________ solar masses = neutron star (densest star). If the core has a mass that is ______________ solar masses = black hole. BLACK HOLE: an object so massive and dense that not even light can escape its gravity NEUTRON STAR: composed of neutrons, 1 teaspoon would weigh 5 x 1012 kg

Think! What are the 5 stages of star life? How are these stages similar and different to human life?

WHY DO WE CARE ABOUT STARS? We get all elements _________________from fusion in stars We get all elements heavier than Iron from ______________ Without stars, we wouldn’t have: ___________________________ which make up our body ___________________________ needed to sustain life