The cluster origin of the solar system -...
Transcript of The cluster origin of the solar system -...
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?
Perseus arm
Sagitarius arm
• http://idw-online.de/pages/de/newsimage?id=69365&size=screenhttp://idw-online.de/pages/de/newsimage?id=69365&size=screen
Dr. Udo Barckhausen, Bundesanstalt für Geowissenschaften und Rohstoffe des Geozentrum Hannover
MeteoritesChondrites - 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
• originated as freely floating, molten or partially molten droplets in space
• Abundances differ little from those of the sun
• formed very early in the history of the solar system
• representative of entire solar system
Birth environment of solar system: Isotopes
Ejected material caught by protoplanetary disc aroundyoung Sun
Supernova exploded at a distance of 0.2-0.3 pc from Sun (F. Adams ARAA 48, 2010)
The onion-like layers of a massive, evolved star just prior to core collapse.
Decay products in chondrites presence of 26Al and 60Fe
26 Al and 60Fe isotopes must have formed by supernova explosion (Williams & Gaidos 2007)
Meteorite abundances determine type of progenitor star for supernova
Massive star with ~25 Msun
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 newlyformed 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 oncircular 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 AUApelion: 937 AUPeriod: 11400 yrEccentricity: 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 Sedna orbitmass distribution
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
30AU cut-off in mass distribution
Sedna orbit
Circular orbits of planets
Supernova within 0.2pc 25 Msun progenitor
Encounter or photo-evaporation Both require high stellar density If encounter with solar type star, then rmin =100-1000AU
Stellar density at solar system location
System undisturbed for solar system age > 30 Myr
The Solar System birth cluster:
Sevaral 103Msun < Mcluster < several 104 Msun
103 Msun/ pc3 < ρcentral < 104 Msun/pc3
Nstar > 1000 Radio-isotopes Adams (2010)
Nstar > 4000 Chemical composition
Lee et al. (2008)
Nstar< 105 Radiation field Adams (2010)
ρcentral<103 Msunpc-3 Sedna orbit Brasser (2008)
ρcentral<104Msunpc-3 Sedna orbit Schwamb (2011)
Estimates or simulations of encounter probabilities in clusters of different size or density:
Mean stellar mass in cluster: 0.5 Msun
Sun close to massive star
Sun close to cluster
center
Mass segregationMany young cluster are
mass segregated
Massive stars are predominantly found in
central regions of cluster
ONC – all O stars are within 0.5pc
Density distribution in young clusters
Requirement for solar birth clustercentral stellar density: 103 – 104 stars/ pc 3
Inside cluster:High stellar density at center, but steepsteep gradient towardsoutskirts
Central density of 103 – 104 stars/ pc 3
translates into average density 10 – 1000 stars/ pc 3
The Solar System birth cluster:
Sevaral 103Msun < Mcluster < several 104 Msun
10 Msun/ pc3 < ρmean < 1000 Msun/pc3
Nstar > 1000 Radio-isotopes Adams (2010)
Nstar > 4000 Chemical composition
Lee et al. (2008)
Nstar< 105 Radiation field Adams (2010)
ρmean<10 Msunpc-3 Sedna orbit
ρmean<1000Msunpc-3 Sedna orbit
Estimates or simulations of encounter probabilities in clusters of different size or density:
Mean stellar mass in cluster: 0.5 Msun
Trapezium in ONC
Quintuplett
High densitymany O stars Gravitational interaction
Photoevaporation Hernandez et al, ApJ 662(2007)
σ Ori cluster
Different young cluster environments
HST image
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
Young clusters with M > 103 Msun
Cluster with same mass as solar birth cluster mass exist today in Milky Way
Note: relatively large error bars for cluster age
Temporal evolution of young clustersCluster mass
No mass lossConsiderablemass loss
Pfalzner 2011
Temporal evolution of young clustersCluster mass
No mass lossConsiderablemass loss
2 cluster types: Snapshots in cluster developmentrather 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
Relation between cluster radius and age givesexpansion velocity in both types of clusters
Star burst clusters:
Rc ~ tc
vexp = 0.1 - 0.2 pc/Myr
Leaky clusters:Rc ~ tc
0.6-0.7
vexp ~ 2pc/Myr
Cluster size gives directly its age
Pfalzner A&A 498, L37,2009
The Solar System birth cluster:
Sevaral 103Msun < Mcluster < several 104 Msun
10 Msun/ pc3 < ρmean < 1000 Msun/pc3
Nstar > 1000 Radio-isotopes Adams (2010)
Nstar > 4000 Chemical composition
Lee et al. (2008)
Nstar< 105 Radiation field Adams (2010)
ρmean<10 Msunpc-3 Sedna orbit
ρmean<1000Msunpc-3 Sedna orbit
Estimates or simulations of encounter probabilities in clusters of different size or density:
Mean stellar mass in cluster: 0.5 Msun
?
Temporal evolution of young clustersCluster density
Pfalzner A&A 498, L37,2009
2 types of clusters in solar birth cluster mass range
Star burst clusters ρc ∼ Rc
-3 Diffusion
Leaky clusters OB associations
ρc ~ Rc-4
Diffusion + Ejection
Radius-age transformation1 Myr 20 Myr 1 Myr 20 Myr
Radial development translates into age development Age
Solar birth cluster a Starburst-Cluster?
average density of 10 – 103 stars/ pc 3
Overlap with starburst
clusters after 5Myr
But ...
Starburst cluster
Leaky-Cluster
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 system has likely developed in leaky cluster environment
Solar birth cluster a leaky cluster?
Density development ρc ~ C t-3.7
Interaction with other stars unlikely after solar system gives naturally circular orbits
average density of 10 – 103 stars/ pc 3
Overlap in early stages of development
Starburst cluster
Leaky-Cluster
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
Average encounterAverage encountereffect on protoplanetare effect on protoplanetare disc in clusterdisc in cluster
Only coplanar, prograde encounters
Cluster simulation
Encounter simulation
Dynamical model of clusters single stars no gas component Code: NBODY6++ List of encounter parameters for all
Modelling of the solar birth cluster development
Gas expulsion at end of star formationprobably 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 encounterwith 100 AU <rperi< 1000 AU
Encounter probabilty functionof cluster density
Higher density=higher likelihood of encounter
But very high densities
Multiple or close encounters No solar system
Resulting encounter history
Probabilty of encounter as function of solar system age
Probability of encounter decreases with cluster age
During 1st Myr after gas expulsion30% 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
Leaky cluster: ρc ~ C t-3.7
Encounter partner history
Solar-type stars mainlyhave 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 historyEccentricity of encounterfunction of cluster density
Dense clustersStrongly hyperbolic encounters
Less dense clustersnearly 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?
1. Spreading and mass loss during first 20Myr
Why are we not still within this birth cluster?
1. Spreading and mass loss during first 20Myr
2.Solar system circles around Galactic Center
v = 220 km/sec r = 8kpc tsun= 4.57 109 yr
About 22 orbits since its formation
Tidal disruption of cluster
Portegies Zwart (2010)
Today the solar system is located in a relatively sparse area of the Milky Way
local stellar density:0.122 stars/pc3
Perseus arm
Sagitararius arm
Artist‘s impression of the nightsky in a cluster
Scientific American, Ron Miller
Impression of thenight sky when the sun was born
Sun formed in a massive cluster
Such clusters exist in two forms Starburst and leaky cluster
Sun most likely formed in leaky cluster
Density development ρc ~ C t-3.7
Solar system forming encounter:• low mass star• highly eccentric orbit