Interstellar Medium, Star and Planet Formation Robi Banerjee Hamburger Sternwarte [email protected] General Information Get your points: • Tutorials (2 weeks) • Exam: 19/20. January ? • Credit Points: 6 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 2 Literature • Frank Shu The Physical Universe, Univ Science Books, 1982 • Weigert, Wendker & Wisotzki Astronomie und Astrophysik, Wiley-VCH, 2009 • Bruce Draine Physics of the Interstellar and Intergalactic Medium, Princeton Univ. Press 2011 • Lyman Spitzer Physical Processes in the Interstellar Medium, John Wiley & Sons, 1998 • Steven Stahler & Francesco Palla The Formation of Stars, Wiley-VCH, 2004 • Peter Bodenheimer Prinicples of Star Formation, Springer, 2011 • Derek Ward-Thomson & Anthony Whitworth An Introduction to Star Formation, Cambridge Univ. Press, 2011 • Norbert Schulz The Formation and Early Evolution of Stars, Springer, 2012 • Eds. Hubert Klahr & Wolfgang Brandner Planet Formation, Cambridge University Press, 2011 • Philip Armitage The Physics of Planet Formation, Cambridge University Press, 2009 • ... ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 3 Overview • ISM (three phases + physical properties) • Molecular clouds (observations + physical properties) • Conditions for star formation (i.e. cold dense regions, Jeans criterion, BE spheres) • Turbulence (Larson’s relation, Kolmogorov turbulence) • Fragmentation • Initial mass function (reconstruction from observations) • IMF (theoretical ideas, conversion from CMF to IMF) • The collapse (1D calculations: Larson/Penston, Shu) • Magnetic fields: mass-to-flux ratio, ambipolar diffusion • Magnetic fields: observational techniques (polarisation, Zeeman, RM) • 3D collapse: disc formation, Jets • Jet launching • Observations of Jets • Formation of Massive stars • Feedback (HII-Regions, SN) + triggered star formation • Protostellar evolution (Hayashi track, classes) • Evolution of protoplanetary discs • Planet formation (grav. instability, core accretion models) ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 4 Overview • Stars have a finite life time e.g. Sun ~ 10 Gyrs but massive stars live only a few Myrs ⟹ stars must have a beginning ⟹ star formation • star formation rate in the Milky Way: 3 - 5 stars / year (cf. SNe: ~ one/50 years) • young scientific branch of Astronomy & Astrophysics (~ 1950er) ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 5 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 6 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 7 Star Formation Questions: • Where do stars form? (galaxies, molecular clouds, dark clouds, Bok-Globules) •Under which conditions do stars form? (gravitational instability) • How do molecular clouds form and evolve? • What determines the star formation rate? • What determines the stellar mass distribution (initial mass function, ISM)? • ... ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 8 Sites of Galactic Star Form • Milky Way consists of ~ 100 billion stars and gas + dust = Interstellar Medium (ISM) (+ radiation, cosmic rays, magnetic fields, ...) • Stars form in dark/molecular clouds (only few % of the galactic volume) ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 9 Edward Barnard 1920: discovery of dark cloudsISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 10 Star Formation sites example: Orion-Nebula • emission nebula • D ~ 500 pc • R ~ 9 pc ESO: VLT ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 11 Hubble Teleskop: Sternentstehungsgebiet NGCISM, 604 Star- inand M33Planet Formation,Galaxie WS (Dreiecksnebel) 14/15 Robi Banerjee 12 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 13 ESA Herschel Teleskop: SternentstehungsgebietISM, Star- and Planet Formation, WS 14/15 Rosetta Robi Banerjee Nebel14 Hubble Teleskop: “Pillars of Creation” Sternbild: Adler ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 15 Star Formation sites Taurus molecular cloud • infrared observations: ⟹ young proto-stars become visible in dark clouds proto-stars ESO: APEX ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 16 Interstellar Medium Phases of the ISM: 3-phase model (McKee & Ostriker 1977) • regions with various temperatures and densities Weigert, Wendker Wisotzki ⟹ cold, warm and hot phase ⟹ determined by cooling and heating processes ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 17 Star Formation sites Properties of clouds/nebulas: • emission nebula: • emit light: mainly by ionising radiation of massive stars • hot: T ~ 10.000 K • mean densities: 10 − 100 cm-3 • dark clouds / Bok Globule: • dense and compact regions, absorb light (mainly dust): • mean densities: 103 − 105 cm-3 • cold: 6 − 20 K • reflection nebula: • visible by reflecting light • don’t contain ionising stars Merope-Nebel ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 19 Magnetic Fields M51 Galaktisches B-Feld (e.g. R.Beck 2001) Polarisationkarte des Pfeifennebels großskalige Komponente: ~ 4µG F.O.Alves, Franco, Girart 2008 Gesamtstärke: ~ 10µG ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 20 Bok* Globule * Bartholomeus Bok (1906-1983) • localised star forming regions • often protostars visible in IR radial density profile • hydrostatic equilibrium? ⟹ Bonnor-Ebert sphere (1956/55) (William Bonnor, 1920, Rolf Ebert, 1926) Bok Globule: Barnard 68 absorption measurements by Alves, Lada & Lada 2001 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 21 Gravitational Collapse critical mass: Jeans Masse MJ • warm neutral interstellar Medium: • T ≈ 5000 K ⟹ cs ≈ 5.7 km/sec • n ≈ 1 cm-3 ⟹ ρ ~ 10-24 g cm-3 7 • ⟹ MJ ≈ 10 M⨀ • ⟹ no collapse / no star formation • Bok Globule: • T ≈ 10 K ⟹ cs ≈ 0.2 km/sec • n ≈ 105 cm-3 ⟹ ρ ~ 4×10-19 g cm-3 • ⟹ MJ ≈ 1 M⨀ • ⟹ sites of individual star formation ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 22 Protostellar Phases • collapse proceeds quickly: 5 dynamical time scales tff ~ 10 yr ⟹ free-fall time • gravitational energy can be released until gas becomes optically thick isothermer Kollaps ⟹ gas core heats up Larson 1969 ⟹ contracts adiabatically ⟹ Hayashi-Track pre main sequence star, PMS ⟹ birth of a proto-star ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 23 Hayashi Track credits: CSIRO Australia ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 24 Protostellar Evolution ISM, Star- and Planet Formation,Bachiller, WS 14/15 RobiARAA Banerjee 199625 Disc evolution Bachiller, ARAA 1996 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 26 Protostars Tobin et al., Nature 2012 • L1527 IRS: youngest protostar at that time t < 300.000 yr M ~ 0.2 M⨀ −7 dM/dt ~ 6.6×10 M⨀/yr ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 27 Protostars • protostars are deeply embedded in dusty envelopes ⟹ re-emission of infrared radiation NICMOS: near infrared camera: 0.8 − 2.5 µm ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 28 Herbig-Haro Objekte 1000 AU ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 29 Herbig-Haro Objects ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 30 1000 AU NGC 1333, Spitzer Telescope, IRAC, NASA, JPL ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 31 1000 AU “Mysitc Mountain” in ISM,Carina Star- and PlanetNebula, Formation, HST,WS 14/15 NASA, Robi Banerjee ESA32 Jets Pudritz & Norman 1986 • Jet launching? ⟹ Lorentz force ⟹ Magnetic fields + disc ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 33 ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 34 Turbulence and Fragmentation ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 35 Mass distribution of stars ⟹ Initial Mass Function (IMF) Munch et al. 2002: Orion Trapezium Cluster ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 36 Formation of Massive Stars Radiation • Problem: most of the mass gets accreted while the star is on the main sequence ⟹ strong radiation pressure ⟹ Eddington Limit ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 37 Entstehung massereicher Sterne Hubble Space Telescope: R 136 in LMC ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 38 Protostellar/Protoplanetary discs ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 39 Extrasolar Planets • list of extrasolar planets: The ExtrasolarPlanets Encyclopaedia http://exoplanet.eu ⟹ by October 2014: ~ 1800 planets • Kepler Mission / NASA: • space telescope main mission: March 2009 - Aug. 2013 since K2-mission (reduced capabilities) • search for extrasolar planets by transit method ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 40 Formation of Planets • coeval formation of stars and planets ⟹ from protoplanetary disc around young star • growth of dust particles to planetesimals d ~ few km → “Core Accretion” (Safronov 1969) → further growth by gravitational focusing • gas giants (like Jupiter)? ⟹ accretion by gravitational attraction ⟹ gravitational instability in the disc (Toomre instability) ISM, Star- and Planet Formation, WS 14/15 Robi Banerjee 41.