Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
First observation of gravitational waves wikipedia , lookup
Planetary nebula wikipedia , lookup
Main sequence wikipedia , lookup
Big Bang nucleosynthesis wikipedia , lookup
Stellar evolution wikipedia , lookup
Cosmic microwave background wikipedia , lookup
Gravitational lens wikipedia , lookup
Expansion of the universe wikipedia , lookup
Cosmic distance ladder wikipedia , lookup
Nucleosynthesis wikipedia , lookup
Search for Life in the Universe Chapter 1 A Universe of Life? (Part 1) 5/22/2017 AST 248, Fall 2005 1 Announcement • Astronomy Open Night: talks to the public about astronomical topics of interest, followed by observing on the roof of the ESS Building, weather permitting • Time and place: First Friday of each month at 7:30 PM in ESS 001 (big lecture hall) • See the Fall 2005 Program 5/22/2017 AST 248, Fall 2005 2 Outline • • • • • • • • Is There Life Elsewhere? Life in the Solar System Nearby Stars Distant Stars in Our Galaxy Numbers of Stars Distances of Stars Communications and Travel Universal Astrophysics (Part 1) – Expansion and Finite Lifetime of the Universe 5/22/2017 AST 248, Fall 2005 3 Is There Life Elsewhere? • Hollywood picture ignores basic physics, chemistry, biology, and astronomy • No credible UFO sighting (TBD in detail) • Our task: scientific search for life, based on physics, chemistry biology, and astronomy • Science evolves: we know today much more than we knew before • But science is also always incomplete 5/22/2017 AST 248, Fall 2005 4 Life in the Solar System • • • • • No civilization except ours, present or past Look for habitable worlds Evidence that Mars once had water Evidence for water under the ice of Europa Evidence for microbal life on Earth under harsh conditions Search for evidence of microbes • Controversial Martian microbes 5/22/2017 AST 248, Fall 2005 5 Nearby Stars • Many extrasolar giant planets (like Jupiter) discovered since 1995 • Detection by reflex motion of parent star • A few transitions seen • Terrestrial planets still below detection limit • Giant extrasolar planets very prevalent in nearby stars • No information, so far, on habitability 5/22/2017 AST 248, Fall 2005 6 Distant Stars in Our Galaxy • Harder to detect microbal life • Search for Extraterrestrial Intelligence: SETI • Main signature: radio transmission 5/22/2017 AST 248, Fall 2005 7 Numbers of Stars • • • • The Solar System has just one star: the Sun ~1011 stars in our Milky Way galaxy ~109 galaxies in the observable universe With planets so prevalent, shouldn’t we expect life to exist elsewhere? • Can we calculate the probability of life? • Can we detect extraterrestrial life? • Is it intelligent? 5/22/2017 AST 248, Fall 2005 8 Sizes to scale, distances not to scale 5/22/2017 AST 248, Fall 2005 9 5/22/2017 AST 248, Fall 2005 10 Distances of Stars • 1 astronomical unit (AU) = Earth-Sun distance: 1.5 x 108 km (9.3 x 107 miles) • Equals 500 light seconds (8 min. 20 sec.) • Distance to nearest star, Cen: 4 light years • Distance to Galactic Center: 2.5 x 104 light years • Distance to the nearest big galaxy, Andromeda (M31): 2 x 106 light years 5/22/2017 AST 248, Fall 2005 11 Communications & Travel • Communication at the speed of light c: – 4 years to Cen – 2.5 x 104 years to the Galactic Center – 2 x 106 years to Andromeda • Travel at ~10-4x c: – 4 x 104 years to Cen – 2.5 x 107 years to the Galactic Center – 2 x 109 years to Andromeda 5/22/2017 AST 248, Fall 2005 12 Universal Astrophysics (Part 1) • Universal laws of physics ultimately govern all processes • Homogenous expansion of the universe similar physical development everywhere: – Gravity Galaxies, stars, and planets – Nucleosynthesis abundances of elements • Instabilities & chaos different objects at different places (galaxies/stars/planets, intergalactic/stellar/planetary space) 5/22/2017 AST 248, Fall 2005 13 5/22/2017 AST 248, Fall 2005 14 Expansion and Finite Lifetime of the Universe • Hubble expansion v12 r12: – Finite age – Early universe dense and hot • Cosmic Microwave Background (CMB): – Detected, present temperature 2.7 K • Big-bang nucleosynthesis: – Correctly predicts primordial abundances of the light elements – There is further nucleosynthesis in stars heavier elements • Small-scale CMB anisotropies: – Detected primordial perturbations gravitational instabilities – Deduced precise age of the universe (2003): 13.7±0.2 x 109 yr 5/22/2017 AST 248, Fall 2005 15 5/22/2017 AST 248, Fall 2005 16 5/22/2017 AST 248, Fall 2005 17