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THE BIRTH OF STARS AND PLANETARY SYSTEMS

THE BIRTH OF STARS AND PLANETARY SYSTEMS. Stephen E. Strom National Optical Astronomy Observatory 07 January, 2003. Overview of Presentation. Theoretical overview Confrontation with theory: what we know and how we know it Current key questions Answering key questions. Theory.

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THE BIRTH OF STARS AND PLANETARY SYSTEMS

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  1. THE BIRTH OF STARS AND PLANETARY SYSTEMS Stephen E. Strom National Optical Astronomy Observatory 07 January, 2003

  2. Overview of Presentation • Theoretical overview • Confrontation with theory: • what we know and how we know it • Current key questions • Answering key questions

  3. Theory

  4. Stellar Conception • A star’s life begins in darkness, in an optically opaque molecular cloud • Shielded by dust and gas from galactic starlight and cosmic rays, the cloud cools • In the densest clumps of molecular gas, gravity overcomes internal pressure: clumps contract

  5. Pressure ~ T Gravity ~ M/R2 A Collapsing Molecular Clump

  6. Stellar Gestation • Clumps are initially spinning as well • a result of tidal encounters among clumps • Spinning, collapsing clumps produce: • a flattened envelope from which material flows toward a …. • circumstellar disk, through which material flows toward a…. • central, prestellar core (a “stellar seed”)

  7. Spinning Protostellar Core

  8. Accretion Disk Stellar seed Infalling envelope Forming the Star-Disk System

  9. Building a Full-Term Star • Gas and dust transported: envelope accretion disk stellar seed • Stellar mass builds up over time (~ 1 Myr) • Accreting material arises from regions that rotate • absent a way of slowing down the star, the star will rotate so rapidly that material is flung off the equator • a star cannot reach ‘full-term’ absent spin regulation • Stellar winds and jets act as ‘rotation regulators’

  10. Wind/Jet Rotating accretion disk Infalling gas/dust Forming star Accreting material Building a Full-term Star removes angular momentum

  11. A Star in Formation: Artist Conception

  12. Forming Planets • Planets form in circumstellar disks • Two processes may be operative: • disk instabilities leading to rapid agglomeration of gas into giant (Jupiter mass) planets during disk accretion phase • agglomeration of dust into km-size planetesimals • buildup of earth mass solid cores via planetesimal collisions • buildup of gas giants if enough disk gas is available

  13. Formation via Disk Instability Forming Jupiter

  14. Formation via Agglomeration; Collisions Growth of larger bodies via collisions Planetesimal swarm formed via collisions among small dust grains Mature planets

  15. Star and Planet Formation Summary Molecular Cloud Rotating Clump Forming Star + disk

  16. Confrontation with theory:What we know and how we know it

  17. Stellar Conception • Radio maps of molecular clouds reveal rotating pre-stellar clumps • diagnosed via tracers of dense, cold gas: CO, CS • Observations of multiple molecules provide • temperature • density • clump mass • kinematics: internal gas motions; rotation • Clump self-gravity exceeds internal pressure

  18. Star-Forming Molecular Cloud 30 Light Years Ophiuchus Molecular Cloud (d ~ 500 light years)

  19. Opaque Molecular Clump 0.2 light years

  20. Stellar Gestation • Doppler analysis (mm-wave) of gas motions shows • clumps are collapsing • clumps are rotating • Hubble Space Telescope observations reveal • flattened envelopes • opaque disks embedded within envelopes • central star • Doppler analysis (infrared) of gas motions shows • gas accreting onto the central star

  21. Disks and Envelopes Around Young Stars

  22. Building a Mature Star • Hubble space telescope observations reveal • disks of solar system dimension around young stars • Infrared observations show • spectral signatures expected for accretion disks • Radio observations: disk masses ~ solar system • Doppler analysis (infrared) of gas motions shows • gas accreting onto the central star • winds emanating from star or inner disk • Optical and infrared images reveal • jets emanating from star-disk systems

  23. HST Observes Protoplanetary Disks

  24. HST Observes Edge-on Disk

  25. Diagnosing Disks in the Infrared

  26. Accretion Disks and Stellar Jets

  27. Implications for Planet Building • In combination, these observations suggest: • accretion disks surround all forming stars • disk masses and sizes are similar to our solar system • As a consequence of the processes that give birth to stars, raw material for planet-building is in place

  28. Evidence for Planetesimal Building • Earth-like planets believed built via planetesimal collisions • produce larger bodies • produce small dust grains as a by-product of collisions • Planetesimals not observed directly • In solar system, evidence of collisions comes from • cratering history (moon; other bodies) • inclination of planet rotation axes • Outside solar system, evidence of collisions come from • light scattered earthward by small dust grains • thermal emission from heated grains • Dust grain population decreases with age • similar to solar system record

  29. A Post-Planet-Building Disk HST Observtions of an IRAS-discovered disk

  30. Disk Warping: Evidence of Planets?

  31. Evidence for Extrasolar Planets • Reflex Doppler motions in parent stars • periodic signals indicative of orbital motions • velocity amplitudes + periods yield mass estimates • More than 50 systems now known • many contain multiple planets • unexpected distribution of orbital distances • unfavorable for survival of terrestrial planets • Direct evidence of giant planet planet via eclipse • gas envelope inferred from light curve shape

  32. Detecting Extrasolar Planets

  33. Extrasolar Planetary Systems

  34. Extrasolar Planet Transit

  35. Key Questions & Paths to Answers

  36. Current Key Questions: Planets • When do planets form? • disk accretion phase? • later, following accretion of disk gas? • How diverse are planetary system architectures? • are close-in (r < 1 AU) Jupiter-mass planets favored? • are planets in habitable zones common or rare? • Can we observe extra-solar planets directly? • can we determine atmospheric structure and chemistry ? • can we detect signatures of life ?

  37. When do Planets Form? • Key observations: • probing accretion disks surrounding young stars and searching for tidal gaps diagnostic of forming planets • searching for gaps in beta-Pic-like disks around mature stars • determining accurate ages for star-disk systems • Key facilities • ALMA • next generation O/IR telescopes • SIRTF + current generation telescopes

  38. Diagnosing Planet Formation: GSMT AURA-NIO Point Design 30-m ground-based telescope Emission from tidal gaps

  39. Diagnosing Planet Formation: ALMA Star at 10pc

  40. SIRTF SIRTF: Artist Conception

  41. Locating Candidate Planetary Systems with SIRTF Inflections in spectra can diagnose gaps in dust disks Dust excess can diagnose planetesimal collision rates

  42. Dust Emission from Planet-Forming Disks: Resolving Candidate Mature Systems Gemini observation of Dust Ring Artist conception of system

  43. How Diverse are Planetary System Architectures? • Key observations • Statistical studies of dust distributions • Precise measurements of reflex motions: • continuation of current radial velocity programs • precise proper motion measurements • Key facilities • SIRTF • SIM (Space Interferometry Mission)

  44. Finding Planets: Precise Position Measurements

  45. Space Interferometry Mission SIM can (1) detect earth-like planets around nearby stars (2) determine distribution of planetary architectures from statistical studies of large samples of stars

  46. Observing Planets Directly • Key observations • imaging and spectroscopy • Key theoretical work • develop understanding of how to diagnose life from spectroscopic signatures • Key facilities • Devices designed to enable high contrast imaging; spectroscopy • coronagraphs that block out light from central star • use on current (Gemini; Keck) and future (GSMT) ground-based telescopes • infrared interferometers (ground: e.g. Keck; Large Binocular Telescope) • Terrestrial Planet Finder/Darwin (space)

  47. Diagnosing Mature Planets Spectra diagnose structure and chemistry of planetary atmospheres

  48. Terrestrial Planet Finder TPF will have the ability to image and take spectra of earth-like planets surrounding nearby stars

  49. Current Key Questions: Stars • How does the distribution of stellar masses depend on initial conditions? • chemical abundance? • collisions among molecular clouds? • How has star formation activity changed over the lifetime of the universe?

  50. How Stars of Different Mass Form • Key observations • physical conditions and kinematics in molecular clouds • observations of stellar mass distributions in these clouds • Key facilities • ALMA • high spatial resolution maps of molecular clouds • large ground-based telescopes (Gemini; Keck; GSMT) • photometry and spectroscopy of emerging stellar populations

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