The cluster origin of the solar system S.Pfalzner Max-Planck-Institut für Radioastronomie
Today the solar system is located in a relatively sparse area of the Milky Way local stellar density: 0.122 stars/pc3 Did the solar system form in such an environment? Sagitarius arm Perseus arm
http://idw-online.de/pages/de/newsimage? id=69365&size=screenhttp://idwonline.de/pages/de/newsimage? id=69365&size=screen. Udo Barckhausen, Bundesanstalt für Geowissenschaften und Rohstoffe des Geozentrum Hannover
Meteorites Chondrites - unmolten meteorites 86.2% of meteorites found on Originate from primitive astroids not been modified due to melting contain chondrules mm-cm sized silicate droplets formed very early in the history of the solar system representative of entire solar system
Birth environment of solar system: Isotopes Decay products in chondrites presence of 26Al and 60Fe Al and 60Fe isotopes must have formed by supernova explosion (Williams & Gaidos 2007) 26 Meteorite abundances determine type of progenitor star for supernova Massive star with ~25 Msun Ejected material caught by protoplanetary disc around young Sun The onion-like layers of a massive, evolved star just prior to core collapse. Supernova exploded at a distance of 0.2-0.3 pc from Sun (F. Adams ARAA 48, 2010)
Birth environment of solar system: Initial mass function Sun formed close to massive star with ~25 Msun Massive stars do not form in isolation but as part of clusters of stars IMF: distribution in mass of a newly formed stellar population massive star with ~25 Msun Sun must have formed in a cluster of several 1000 stars
Infos from Meteorits Solar system formed: In a star cluster Nstars > 1000 stars In vicinity of supernova Distance to supernova 0.2-0.3 pc
Solar System properties Mass distribution in Solar System: Sun Planets Kuiper belt Oort cloud Planets mostly on circular orbits System was not perturbed inside 30 AU
Relicts of the Solar System history: Mass distribution Mass distribution in Solar System: 30 AU drop in mass distribution (Bernstein et al. 2004) What can cause such a drop? Encounter during disc phase Photoevaporation during disc phase Binary star
Relicts of the Solar System history: Mass distribution Mass distribution in Solar System: 30 AU drop in mass distribution (Bernstein et al. 2004) What can cause such a drop? Encounter during disc phase Photoevaporation during disc phase (Mann & Williams 2009) Binary star UV radiation
Relicts of the Solar System history: Sedna trans-neptunian object discovered in 2003 Perhelion: 76 AU Apelion: 937 AU Period: 11400 yr Eccentricity: 0.8527 High eccentricity of Sedna NOT caused by planets (Gaidos et al. 2005) Possible explanation: Encounter (Moribelli & Levison 2004) But circular orbits of planets No encounter after solar system formed (30 Myr) (Malhorta 2008)
Relicts of the Solar System history: Mass distribution and Sedna orbit Mass and dynamics in Solar System: 30 AU drop in mass distribution Sedna orbit What can cause drop and Sedna orbit? Encounter during disc phase What kind of encounter is necessary to obtain these two features? 100-1000 AU encounter (for summary see Adams 2010) Encounter assumptions: solar-type star coplanar, prograde cut-off at 1/3 periastron
Limits on Solar System birth environment: Meteorit composition Supernova within 0.2pc 25 Msun progenitor 30AU cut-off in mass distribution Encounter or photo-evaporation Both require high stellar density If encounter with solar type star, then rmin =100-1000AU Sedna orbit Stellar density at solar system location Circular orbits of planets System undisturbed for solar system age > 30 Myr
The Solar System birth cluster: Estimates or simulations of encounter probabilities in clusters of different size or density: Nstar > 1000 Radio-isotopes Adams (2010) Nstar > 4000 Chemical composition Lee et al. (2008) Nstar< 105 Radiation field Adams (2010) ρ central<103 Msunpc-3 Sedna orbit Brasser (2008) ρ central<104msunpc-3 Sedna orbit Schwamb (2011) Mean stellar mass in cluster: 0.5 Msun Sevaral 103Msun < Mcluster < several 104 Msun 103 Msun/ pc3 < ρ central < 104 Msun/pc3
Mass segregation Many young cluster are mass segregated Massive stars are predominantly found in central regions of cluster Sun close to massive star ONC all O stars are within 0.5pc Sun close to cluster center
Density distribution in young clusters Requirement for solar birth cluster central stellar density: 103 104 stars/ pc 3 Inside cluster: High stellar density at center, but steep steep gradient towards outskirts Central density of 103 104 stars/ pc 3 translates into 3
The Solar System birth cluster: Estimates or simulations of encounter probabilities in clusters of different size or density: Nstar > 1000 Radio-isotopes Adams (2010) Nstar > 4000 Chemical composition Lee et al. (2008) Nstar< 105 Radiation field Adams (2010) ρ mean<10 Msunpc-3 Sedna orbit ρ mean<1000msunpc-3 Sedna orbit Mean stellar mass in cluster: 0.5 Msun Sevaral 103Msun < Mcluster < several 104 Msun 10 Msun/ pc3 < ρ mean < 1000 Msun/pc3
Different young cluster environments Quintuplett Trapezium in ONC σ Ori cluster High density many O stars HST image Gravitational interaction Photoevaporation Hernandez et al, ApJ 662(2007)
Young clusters with M > 103 Msun Most stars form in clusters Lada & Lada (2003) Many more clusters with ages < 10 Myr than at older ages for same time span Clusters dissolve early on in development Note: relatively large error bars for cluster age Cluster with same mass as solar birth cluster mass exist today in Milky Way
Temporal evolution of young clusters Cluster mass No mass loss Considerable mass loss Pfalzner 2011
Temporal evolution of young clusters Cluster mass No mass loss Considerable mass loss 2 cluster types: Snapshots in cluster development rather than multitude of cluster types
Starburst cluster -Sequenz Trumpler14 1 Myr 20 Myr
Densities of young clusters with M > 103 Msun What about the densities of these young massive clusters? The mass density of such young clusters spans 7 orders of magnitude: From ~0.01 to 105 Msun pc-3 Pfalzner A&A 498, L37,2009
Expansion velocity Leaky clusters: Rc ~ tc0.6-0.7 vexp ~ 2pc/Myr Star burst clusters: Rc ~ t c vexp = 0.1-0.2 pc/myr Pfalzner A&A 498, L37,2009 Relation between cluster radius and age gives expansion velocity in both types of clusters Cluster size gives directly its age
The Solar System birth cluster: Estimates or simulations of encounter probabilities in clusters of different size or density: Nstar > 1000 Radio-isotopes Adams (2010) Nstar > 4000 Chemical composition Lee et al. (2008) Nstar< 105 Radiation field Adams (2010) ρ mean<10 Msunpc-3 Sedna orbit ρ mean<1000msunpc-3 Sedna orbit Mean stellar mass in cluster: 0.5 Msun? Sevaral 103Msun < Mcluster < several 104 Msun 10 Msun/ pc3 < ρ mean < 1000 Msun/pc3
Temporal evolution of young clusters Cluster density Pfalzner A&A 498, L37,2009
2 types of clusters in solar birth cluster mass range Star burst clusters ρ c Rc-3 Diffusion Leaky clusters OB associations ρ c ~ Rc-4 Diffusion + Ejection
Radius-age transformation 1 Myr 20 Myr 1 Myr 20 Myr Radial development translates into age development Age
Solar birth cluster a Starburst-Cluster? Starburst cluster average density of 10 103 stars/ pc 3 Overlap with starburst clusters after 5Myr Leaky-Cluster But... During first 5 Myr density in starburst clusters extremely high Many close encounters Discs would be destroyed No planetary system Starburst cluster unlikely solar birth environment
Solar birth cluster a leaky cluster? Starburst cluster average density of 10 103 stars/ pc 3 Overlap in early stages of development Leaky-Cluster Density development ρc ~ C t-3.7 Interaction with other stars unlikely after solar system gives naturally circular orbits Solar system has likely developed in leaky cluster environment
Solar system formed in the central regions of a leaky cluster Initially high stellar density: What does that means for the solar system?
Modelling of solar birth cluster Cluster simulation Encounter simulation Dynamical model of clusters single stars no gas component Code: NBODY6++ List of encounter parameters for all Only coplanar, prograde encounters Average encounter effect on protoplanetare disc in cluster
Modelling of the solar birth cluster development Gas expulsion at end of star formation probably resposible for cluster expansion Uncertainities in gas expulsion process Instead: Model clusters at different densities ONC-like cluster profile Sun formed close to massive star Solar-type stars close to cluster center
Probability of solar system forming encounter Single encounter with 100 AU <rperi< 1000 AU Encounter probabilty function of cluster density Higher density= higher likelihood of encounter But very high densities Multiple or close encounters No solar system
Resulting encounter history Leaky cluster: ρ c ~ C t-3.7 Probabilty of encounter as function of solar system age Probability of encounter decreases with cluster age During 1st Myr after gas expulsion 30% chance of solar system forming encounter Such an encounter likely event for solar-type star close leaky cluster center After 3-4 Myr significantly reduced encounter probability
Encounter partner history Solar-type stars mainly have encounter with Low-mass stars mstar< 0.5 Msun High-mass stars mstar< 10 Msun With a preference for low mass stars This preference for encounters with low-mass stars decreases the older the cluster becomes
Encounter eccentricity history Eccentricity of encounter function of cluster density Dense clusters Strongly hyperbolic encounters Less dense clusters nearly parabolic encounters If encounter was early on in cluster developemnt (< 2Myr) then Most likely strongly hyperbolic encounter
Why are we not still within this birth cluster? Spreading and mass loss during first 20Myr
Why are we not still within this birth cluster? Spreading and mass loss during first 20Myr olar system circles around Galactic Center About 22 orbits since its formation Tidal disruption of cluster v = 220 km/sec Portegies Zwart (2010) r = 8kpc tsun= 4.57 109 yr
Today the solar system is located in a relatively sparse area of the Milky Way local stellar density: 0.122 stars/pc3 Sagitararius arm Perseus arm
Sun formed in a massive cluster Such clusters exist in two forms Starburst and leaky cluster Impression of the night sky when the sun was born Sun most likely formed in leaky cluster Density development ρ c ~ C t-3.7 Solar system forming encounter: low mass star highly eccentric orbit Scientific American, Ron Miller Artist s impression of the nightsky in a cluster