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


Theory: Theory


Stellar Conception: 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


A Collapsing Molecular Clump: A Collapsing Molecular Clump


Stellar Gestation: 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')


Spinning Protostellar Core: Spinning Protostellar Core


Forming the Star-Disk System: Forming the Star-Disk System


Building a Full-Term Star: 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’


Building a Full-term Star: Building a Full-term Star removes angular momentum


A Star in Formation: Artist Conception: A Star in Formation: Artist Conception


Forming Planets: 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


Formation via Disk Instability: Formation via Disk Instability Forming Jupiter


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


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


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


Stellar Conception: 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


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


Opaque Molecular Clump: Opaque Molecular Clump 0.2 light years


Stellar Gestation: 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


Disks and Envelopes Around Young Stars: Disks and Envelopes Around Young Stars


Building a Mature Star: 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


HST Observes Protoplanetary Disks: HST Observes Protoplanetary Disks


HST Observes Edge-on Disk: HST Observes Edge-on Disk


Diagnosing Disks in the Infrared: Diagnosing Disks in the Infrared


Accretion Disks and Stellar Jets: Accretion Disks and Stellar Jets


Implications for Planet Building: 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


Evidence for Planetesimal Building: 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


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


Disk Warping: Evidence of Planets?: Disk Warping: Evidence of Planets?


Evidence for Extrasolar Planets: 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


Detecting Extrasolar Planets: Detecting Extrasolar Planets


Extrasolar Planetary Systems: Extrasolar Planetary Systems


Extrasolar Planet Transit: Extrasolar Planet Transit


Key Questions & Paths to Answers: Key Questions andamp; Paths to Answers


Current Key Questions: Planets: 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 andlt; 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 ?


When do Planets Form?: 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


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


Diagnosing Planet Formation: ALMA: Diagnosing Planet Formation: ALMA Star at 10pc


SIRTF: SIRTF SIRTF: Artist Conception


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


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


How Diverse are Planetary System Architectures?: 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)


Finding Planets: Precise Position Measurements: Finding Planets: Precise Position Measurements


Space Interferometry Mission: 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


Observing Planets Directly: 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)


Diagnosing Mature Planets: Diagnosing Mature Planets Spectra diagnose structure and chemistry of planetary atmospheres


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


Current Key Questions: Stars: 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?


How Stars of Different Mass Form: 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


Slide51: Probing the IMF: Measurements = 7' Stellar density ~ 100x Orion Nebula Cluster Galactic Center Superclusters: d = 10 kpc


Slide52: Probing the IMF: Measurements Stellar density ~ 10x Orion Nebula Cluster LMC Massive Cluster: d = 200 kpc


Slide53: Probing the IMF: Measurements M82 Superclusters: d = 4 Mpc


Star Formation: From the First Stars to the Current Epoch: Star Formation: From the First Stars to the Current Epoch Key observations trace star formation rate to earliest epochs study starburst systems star formation rates distribution of stellar masses Key facilities NGST (multi-wavelength photometry) large ground-based telescopes (spectroscopy)


Slide55: JWST will observe first generation stars


GSMT will enable analyis of distant star-forming regions: GSMT will enable analyis of distant star-forming regions HST GSMT


Possible Near-term Milestones: Possible Near-term Milestones SIRTF: Infer range of planetary architectures from infrared spectral energy distributions Infer planetesimal collision rates as a function of age from 1 Myr to 5 Gyr Ground-based telescopes Direct imaging of exo-planet Spectroscopy of exo-planet