Science and Creationism 3. Astronomy © Colin Frayn,

© Colin Frayn, Do we know how stars form? Of course we do! Stellar formation is extremely well understood –Observations Star forming regions in nebulae Galactic mergers Clusters of stars –Computations Analytical calculations using physical laws Computational simulations of physics Computational mathematical models

© Colin Frayn, Angular Momentum The Sun should be spinning more –99% of the mass but <2% of the angular momentum –No problem, magnetic braking explains this Magnetic field of sun interacts with proto-planetary disk Slows down the sun’s rotation Some planets are spinning in the wrong direction –Venus is the only planet that spins clockwise –Probably due to a catastrophic early event Or maybe drag forces in the early solar system Some moons are orbiting in the wrong direction –Almost all moons spin anti-clockwise, but some don’t –They were gravitationally captured They strayed close to the planet and got caught

© Colin Frayn, Stellar Wind in the Early Solar System Will stellar wind push away material before planets can form? –Other forces compete Gravity –Gravity pulls dust and debris in towards the star –Directly counters the stellar wind Particle size –Acceleration inversely proportional to particle size –As size increases, effect of stellar wind reduces –Exact details not yet understood There’s no fundamental problem!

© Colin Frayn, Star formation in action Images courtesy NASA Star forming globules in the Eagle Nebula, M16 Star forming regions in the colliding Antennae galaxies

© Colin Frayn, Star formation in action (2) Images courtesy NASA Newly born stars in the PleiadesA protoplanetary disk in the Orion Nebula

© Colin Frayn, How old are stars? Our sun is about 4.6 billion years old –It is half way through its life –This is very well established Stars have the potential to live a very long time –Smaller stars live longer –Very massive stars live relatively short lives A few million years Stellar ages vary enormously –Stars are being formed today Potential ages are much greater than this –Stars could live 10s or 100s of billions of years

© Colin Frayn, Stellar ages The sun is not powered by cooling! Nuclear fusion –We understand the physics of this very well indeed We can create fusion reactions on Earth! We can measure the sun’s energy output We know the processes causing this We know how much fuel the sun has Detailed calculations give ~10B yrs lifespan Simulations agree

© Colin Frayn, Isochrones The life cycle of stars is very well understood, and we can explore it using computational models called Isochrones Our computational models match beautifully to real observations, allowing us to calculate ages for observed objects

© Colin Frayn, Red Sirius Was Sirius once red? –If so, then stellar evolution models are wrong One reliable source : Ptolemy’s Almagest –Ptolemy’s work was interpolated with later additions –Sirius appears red when close to the horizon (because of dust) –Translations are highly ambiguous Chinese astronomers unambiguously agree that Sirius has always been white!

© Colin Frayn, Short Period Comets They have a lifetime of ~10-20,000 yrs so why are they still here? They are replenished from the Kuiper belt This has been directly observed It is a reservoir of objects outside the orbit of Neptune (30 AU) to beyond Pluto (55 AU) Objects can live here indefinitely –It’s cold enough out there –Sun’s heat doesn’t break them up There is no problem here whatsoever Known Kuiper Belt Objects (courtesy Wikimedia)

© Colin Frayn, The Oort Cloud The reservoir for long-period comets Discovered in 1950 This is much further out! –50,000 AU distant! Has not been directly observed Existence is known by examining orbits of long- period comets –So many of these have aphelion at ~50,000+ AU

© Colin Frayn, The Distance Scale Short distances (up to ~1,600 light years) –Parallax Just like when you close alternate eyes Hipparcos satellite (1989) GAIA satellite (2012?) will vastly improve this Standard candles –Variable stars Well established relationships between intrinsic brightness and variability –Supernovae Fundamental physics is very well understood Absolute brightness is well-known These techniques overlap in range Each one can calibrate and verify the next

© Colin Frayn, Shrinking Sun The Sun is losing mass –5Mt per second of mass loss! –Sun can sustain that for roughly 1,000 times the age of the Universe! –Not a problem! Is it shrinking? –Initial study (Dunham et al. 1979) was withdrawn Authors realised they were wrong –All the recent studies say no shrinking –There may be a short-period (80 year) oscillation to explain some early results

© Colin Frayn, Early Faint Sun Sun is 4.6 Gyr old Should have been much fainter when life arose –Solar evolution models predict this –Roughly 25% less solar energy flux on Earth –Would have caused a 7% temperature drop Corresponds to ~20 degrees celsius colder –Not a very big problem Some oceans are degrees celsius all year round Greenhouse effect also counters this Life may have begun at deep sea vents –In which case the solar energy is irrelevant! –Energy comes from hot volcanic water

© Colin Frayn, The Solar Neutrino Problem Models predict that the sun should produce many more neutrinos than are observed This has been comprehensively explained: Neutrinos oscillate into different (previously undetectable) forms on the way to Earth. Problem totally resolved since 2001

© Colin Frayn, Globular clusters Stars in globular clusters seem to be moving apart rapidly; therefore the cluster must be young Globular Cluster M80 (courtesy Wikimedia) No, because of gravity Stars are on orbits! They move towards the edge and then get pulled back in! Just like when you throw a ball up in the air

Too Many Stars A quick calculation: –(numbers may vary) –10 billion galaxies, –Each has 10 billion stars –Universe is 14 billion years old –~15 million stars per minute formed Is this reasonable? Why not? © Colin Frayn,