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
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
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)
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
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”
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
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
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
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
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
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
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!
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
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)
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.
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
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!
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)
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!
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)
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
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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