Download The Solar System birth cluster

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?
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. 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