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.

Transcript

1. How Do We Know the Ages of Stars? Dr. JJ Hermes Hubble Fellow University of North Carolina at Chapel Hill www.jjherm.es
2. How Do We Know the Ages of Stars? Dr. JJ Hermes Hubble Fellow University of North Carolina at Chapel Hill www.jjherm.es
3. V = 13.3 mag Earthrise from NASA’s Lunar Reconnaissance Orbiter
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
5. V = 13.3 mag How Do We Know the Age of The Sun?
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
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)
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
9. Astronomers Cannot Usually Touch The Objects They Study!
10. Light Is the Only Way Know About Anything Outside Our Solar System
11. V = 13.3 mag Hubble space telescope (as seen from Space Shuttle)
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
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”
14. V = 13.3 mag Atacama Large Millimeter Array (ALMA)
15. V = 13.3 mag Atacama Large Millimeter Array (ALMA)
16. V = 13.3 mag ALMA image of gaps in the protoplanetary disk around ‘HL Tau’ “a few tens of thousands of years old”
17. V = 13.3 mag The Sun: Solar Dynamics Observatory “a few billion years old”
18. V = 13.3 mag How Do We Know the Ages of Stars? I. Rotation Rates
19. V = 13.3 mag How Do We Know the Ages of Stars? I. Rotation Rates How fast does the Sun rotate?
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
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
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
23. How Do We Know the Ages of Stars? II. How Bright They Are Stars get their energy from fusing hydrogen to helium
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
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
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
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
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
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!
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
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
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)
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.
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
35. This is Called Spectroscopy Passing SunlightThrough a Prism: This darkest line is from CALCIUM Boston University
36. Hydrogen
37. Helium
38. Sodium
39. Sodium Alwyn Ladell
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
41. 5000 km Swedish Solar Telescope (Earth for scale) How Do We Know the Ages of Stars? VI. Stellar Pulsations (Starquakes)
42. V = 13.3 mag Big Bear Solar Telescope How Do We Know the Ages of Stars? VI. Stellar Pulsations (Starquakes)
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!
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)
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!
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)
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
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