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How do we know the ages of stars?

jjhermes
January 29, 2017

How do we know the ages of stars?

Outreach talk, 40 min. January 2017: Astronomy Days, North Carolina Museum of Natural Sciences, Raleigh, NC, USA.

jjhermes

January 29, 2017
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  1. How Do We Know the
    Ages of Stars?
    Dr. JJ Hermes
    Hubble Fellow
    University of North Carolina at Chapel Hill
    www.jjherm.es

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  2. How Do We Know the
    Ages of Stars?
    Dr. JJ Hermes
    Hubble Fellow
    University of North Carolina at Chapel Hill
    www.jjherm.es

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  3. V = 13.3 mag Earthrise from NASA’s Lunar Reconnaissance Orbiter

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  4. V = 13.3 mag
    If you are 10 years old:
    à you are more than 300 million
    seconds old
    à I am 32 and now more than
    1,000,000,000 seconds old!
    ‘Year’
    For Earth to orbit Sun:
    Year = 365.25 days
    = 31,557,600 seconds

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  5. V = 13.3 mag
    How Do We Know the
    Age of The Sun?

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  6. V = 13.3 mag (Connelly et al. 2012)
    How Do We Know the
    Age of The Sun?
    best current guess:
    4.56730 ± 0.00016 billion years old
    aka 4,567,300,000 ± 160,000 years

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  7. V = 13.3 mag
    How Do We Know the
    Age of The Sun?
    best current guess:
    4.56730 ± 0.00016 billion years old*
    * Radioactive dating
    of meteorites (and
    Earth rocks)

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  8. V = 13.3 mag
    All objects in our
    Solar System (Sun,
    planets, meteors,
    comets, Earth)
    formed at the same
    time from the
    same material

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  9. Astronomers Cannot
    Usually Touch The
    Objects They Study!

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  10. Light Is the Only Way
    Know About Anything
    Outside Our Solar System

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  11. V = 13.3 mag
    Hubble space telescope
    (as seen from Space Shuttle)

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  12. V = 13.3 mag
    Zooming into Orion: Actual images from sky surveys & Hubble space telescope
    Sometimes, it’s a simple as looking directly for very young stars

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  13. V = 13.3 mag recent HST image of active star formation around ‘HH24’
    Sometimes, it’s a simple as looking directly for very young stars
    “a few thousand years old”

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  14. V = 13.3 mag Atacama Large Millimeter Array (ALMA)

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  15. V = 13.3 mag Atacama Large Millimeter Array (ALMA)

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  16. V = 13.3 mag ALMA image of gaps in the protoplanetary disk around ‘HL Tau’
    “a few tens of thousands of years old”

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  17. V = 13.3 mag The Sun: Solar Dynamics Observatory
    “a few billion years old”

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  18. V = 13.3 mag
    How Do We Know the Ages of Stars?
    I. Rotation Rates

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  19. V = 13.3 mag
    How Do We Know the Ages of Stars?
    I. Rotation Rates
    How fast does the Sun rotate?

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  20. V = 13.3 mag
    How Do We Know the Ages of Stars?
    I. Rotation Rates
    How fast does the Sun rotate?
    25.6 days at the Equator
    33.5 days at the Poles

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  21. How Do We Know the Ages of Stars?
    I. Rotation Rates
    ~100 million years old ~1 billion years old ~5 billion years old
    Younger stars rotate faster
    than older stars Kepler space telescope

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  22. Jennifer van Saders et al. 2016
    How Do We Know the Ages of Stars?
    I. Rotation Rates
    Younger stars rotate faster
    than older stars
    Rotation Period (days)
    Age (billions of years)
    0 2 4 6 8 10

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  23. How Do We Know the Ages of Stars?
    II. How Bright They Are
    Stars get their energy from fusing hydrogen to helium

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  24. V = 13.3 mag ~100-million-year-old stars in the Pleiades: NASA/ESA/AURA/Caltech
    How Do We Know the Ages of Stars?
    II. How Bright They Are
    More massive stars burn through their fuel faster

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  25. V = 13.3 mag
    How Do We Know the Ages of Stars?
    III. How Bright They Are in Star Clusters
    Sorting stars by color gives an indication of a star’s evolution

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  26. V = 13.3 mag
    How Do We Know the Ages of Stars?
    III. How Bright They Are in Star Clusters
    More massive stars burn through their fuel faster

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  27. V = 13.3 mag
    How Do We Know the Ages of Stars?
    III. How Bright They Are in Star Clusters
    More massive stars burn through their fuel faster
    ~4 billion yrs old
    ~7 billion yrs old
    M67

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  28. V = 13.3 mag
    How Do We Know the Ages of Stars?
    IV. White Dwarfs: Retired Stars
    All stars eventually run out of fuel
    In about 6 billion years, our Sun will become a white dwarf

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  29. V = 13.3 mag
    How Do We Know the Ages of Stars?
    IV. White Dwarfs: Retired Stars
    White dwarfs evolve simply by cooling:
    If we measure their temperature, we can estimate their age!

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  30. V = 13.3 mag
    How Do We Know the Ages of Stars?
    IV. White Dwarfs: Retired Stars
    (Intrinsic White Dwarf Brightness)
    (Density of White Dwarfs)
    By looking for the
    coolest, white dwarfs
    we can say: The Sun’s
    neighborhood in the
    Galaxy is roughly
    Jason Kalirai 2012
    ~11 billion years old
    Brighter Fainter
    More
    Fewer

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  31. V = 13.3 mag
    Stars >10 times more massive than the Sun explode
    as Supernovae when they run out of fuel!
    before after
    M82, 2014

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  32. V = 13.3 mag
    How Do We Know the Ages of Stars?
    V. How Much Iron They Have
    Ancient stars in M80: Hubble space telescope
    Stars with less iron are older (less enrichment from supernovae)

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  33. V = 13.3 mag
    How Do We Know the Ages of Stars?
    V. How Much Iron They Have
    The iron in our bodies came entirely from exploded stars!
    The Sun and Earth
    formed from a
    cloud of gas and
    dust polluted by
    nearby supernovae.

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  34. V = 13.3 mag
    How Do We Know the Ages of Stars?
    V. How Much Iron They Have
    Spectroscopy: Each atom has its own fingerprint in light

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  35. This is Called Spectroscopy
    Passing SunlightThrough a Prism:
    This darkest line is from CALCIUM
    Boston University

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  36. Hydrogen

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  37. Helium

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  38. Sodium

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  39. Sodium
    Alwyn Ladell

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  40. V = 13.3 mag
    How Do We Know the Ages of Stars?
    V. How Much Iron They Have
    The oldest stars have the fewest metals!
    (less enrichment from supernovae)
    Anna Frebel et al. 2011

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  41. 5000 km
    Swedish Solar Telescope (Earth for scale)
    How Do We Know the Ages of Stars?
    VI. Stellar Pulsations (Starquakes)

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  42. V = 13.3 mag Big Bear Solar Telescope
    How Do We Know the Ages of Stars?
    VI. Stellar Pulsations (Starquakes)

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  43. V = 13.3 mag
    How Do We Know the Ages of Stars?
    VI. Stellar Pulsations (Starquakes)
    Surface convection rings
    the Sun, causing sound
    waves which can be used
    to study the star’s interior!

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  44. V = 13.3 mag
    How Do We Know the Ages of Stars?
    VI. Stellar Pulsations (Starquakes)
    Actual data of the
    Sun’s pulsations!
    Fits to models for
    the Sun show:
    4.57 ± 0.11
    billion years old
    (Bonanno et al. 2002)
    5 min
    6 min 4 min
    7 min
    Birmingham Solar Oscillation Network (BiSON)

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  45. V = 13.3 mag Tiago Campante et al. 2013
    How Do We Know the Ages of Stars?
    VI. Stellar Pulsations (Starquakes)
    • Kepler-444 has 5 planets
    • The host star is 11.2 ± 1.0
    billion years old!

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  46. How Do We Know the
    Ages of Stars?
    I. Their Rotation Rate (old=slow)
    II. How Bright They Are (young=blue)
    III. How Bright They Are in Clusters
    IV. White Dwarfs: Retired Stars (old=cooler)
    V. How Much Iron They Have (old=less)
    VI. Stellar Pulsations (starquakes)

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  47. V = 13.3 mag Artists rendition of Milky Way
    How Do We Know the Ages of Stars?
    VII. Where They Are in the Galaxy
    Halo = Oldest
    Bulge = Young
    Disk = Both

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  48. V = 13.3 mag Melendez et al. 2016
    How Do We Know the Ages of Stars?
    VIII. How Much Lithium They Have
    Age (billions of years)
    Lithium abundance (logarithmic)
    Lithium is depleted in older Sun-like stars

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