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The Astrophysical Origins of the ShortLived Radionuclides in the Early Solar System

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Proton, alpha particle Galactic Cosmic Rays (GCRs) spall ambient nuclei, producing SLRs ... GCR protons spall local CNO nuclei, produce 10Be. 10Be GCRs trapped ... – PowerPoint PPT presentation

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Title: The Astrophysical Origins of the ShortLived Radionuclides in the Early Solar System


1
The Astrophysical Origins of the Short-Lived
Radionuclides in the Early Solar System
  • Steve Desch
  • November 30, 2004
  • UCLA - IGPP

with a shout-out to my ASU supernova posse
Nicolas Ouellette, Jeff Hester, Laurie Leshin,
Gary Huss
2
Outline
  • Short-lived radionuclides
  • What are they?
  • How are they measured?
  • Possible sources
  • Inheritance
  • Irradiation
  • Injection
  • Aerogel model
  • Astrophysical context
  • SLR predictions

3
Short-Lived Radionuclides
SLRs Radionuclides with
half-lives t1/2 lt 16 Myr
Early Solar System SLRs Confirmed by Isotopic
Analyses of Meteorites
41Ca (t1/2 0.1 Myr) (Srinivasan et
al. 1994, 1996) 36Cl (t1/2 0.3 Myr)
(Murty et al. 1997 Lin et al. 2004)
26Al (t1/2 0.7 Myr) (Lee et al. 1976)
60Fe (t1/2 1.5 Myr) (Tachibana Huss 2003
Mostefaoui et al. 2004) 10Be (t1/2
1.5 Myr) (McKeegan et al. 2000 Sugiura et al.
2001) 53Mn (t1/2 3.7 Myr) (Birck
Allegre 1985) 107Pd (t1/2 6.5 Myr)
(Kelly Wasserburg 1978) 182Hf (t1/2 9
Myr) (Harper Jacobsen 1994) 129I
(t1/2 15.7 Myr) (Jeffery Reynolds 1961)
4
Isotopic analyses of meteorites show they once
held SLRs
Excess 10B is from decay of 10Be
Slope gives original 10Be/9Be ratio
Natural 10B / 11B ratio
McKeegan et al. (2000)
5
Initial Abundances of Confirmed SLRs
Possibly 60Fe/56Fe 1.6x10-6
irons
6
Unconfirmed SLRs
7Be (t1/2 57 days) (Chaussidon et al.
2004) 63Ni (t1/2 101 years) (Luck et al.
2003) 97Tc (t1/2 2.6 Myr) (Yin Jacobsen
1998) 99Tc (t1/2 0.21 Myr) (Yin et al.
1992) 135Cs (t1/2 2.3 Myr) (McCulloch
Wasserburg 1978 Hidaka et al. 2001) 205Pb (t1/2
15 Myr) (Chen Wasserburg 1981)
Chaussidon et al (2004)
Luck et al (2003)
7
Inheritance
Sun and Protoplanetary Disk may have inherited
SLRs as a result of Galactic processes Ongoing
Galactic Nucleosynthesis Supernovae, Wolf-Rayet
winds, novae, etc., eject newly created
radionuclides into Galaxy Galactic Cosmic Rays
Proton, alpha particle Galactic Cosmic Rays
(GCRs) spall ambient nuclei, producing SLRs Some
GCR nuclei are SLRs, get trapped in gas that
forms Solar System (Clayton Jin 1995)
8
Ongoing Galactic Nucleosynthesis?
supernovae (and Wolf-Rayet winds) eject
radionuclides
supernova
Stars form in the spiral arms of spiral galaxies
radionuclide-laden gas orbits Galaxy for 100
Myr, until next spiral arm
new stars form with radionuclides
M 109
9
182Hf
129I
26Al
53Mn
60Fe
Harper (1996)
10
Ongoing Galactic Nucleosynthesis
  • Could explain abundance of 129I, with 100 Myr
    delay
  • Could explain other SLRs (182Hf, 107Pd, even
    53Mn), but not without overproducing 129I
  • Does NOT explain abundances of 26Al or 60Fe (even
    w/o delay) Harper (1996) Wasserburg et al.
    (1996) Meyer Clayton (2000)
  • If 60Fe is attributed to ongoing Galactic
    nucleosynthesis, 53Mn, 182Hf and 129I vastly
    overproduced

11
Galactic Cosmic Rays
  • Most GCRs are protons other nuclei present in
    near-solar proportions spacecraft have
    accurately measured fluxes of GCRs of different
    energies (10 MeV/n to gt 10 GeV/n)
  • Beryllium GCRs 106 times more abundant than solar
  • Flux of 10Be GCRs is known and is large
  • Fluxes of all GCRs probably factor of 2 higher
    4.5 Gyr ago

12
Galactic Cosmic Rays
Galactic Cosmic Rays (GCRs) follow magnetic field
lines
Magnetic field lines observed to converge in
star-forming cores GCRs funneled into cloud cores
Schleuning (1998)
13
Some GCRs mirrored out of cloud core by B fields
B fields funnel some GCRs into cloud core
GCRs in cloud core can be trapped if column
density ? is high enough
Cloud core B fields, Desch Mouschovias (2001)
14
Column Density ?(t), Magnetic Field Strength B(t)
calculated (Desch Mouschovias 2001 Desch,
Connolly Srinivasan 2004)
GCRs ionize gas passing through cloud core, lose
energy, slow down (Bethe formula) Low-energy (lt
100 MeV/n) 10Be GCRs are trapped when ?
0.01 g cm-2
15
Desch, Connolly Srinivasan (2004)
total 10Be/9Be

10Be GCRs trapped in cloud core
10Be/9Be in meteorites
GCR protons spall local CNO nuclei, produce 10Be
16
Galactic Cosmic Rays
  • 10Be in meteorites entirely attributable to
    trapped 10Be GCRs
  • Biggest uncertainty is GCR flux 4.5 Gyr ago
    (factor of 2) probably all but at least half of
    10Be is trapped GCRs
  • Trapped GCRs do not explain any other SLR, but
    10Be is known to be decoupled from other SLRs
    (Marhas et al. 2002)
  • Inheritance Conclusions
  • At least half, and probably all, 10Be is
    inherited
  • 129I may be inherited
  • Other SLRs, especially 26Al and 60Fe, are not
    inherited.

17
Irradiation
Energetic particles (accelerated by solar flares
within the Solar System) may have irradiated
material, inducing nuclear reactions and creating
SLRs Solar flares accelerate p, 4He, 3He to E gt
10 MeV/n Particle fluxes 105 times larger around
T Tauri stars in 1 Myr, 1048 (!) energetic
particles emitted Irradiation within the
Disk Gas and dust in the protoplanetary disk (
1 AU) Irradiation within the Suns
Magnetosphere Solids only, inside 0.1 AU
18
Irradiation in the Disk
If gas is present, energetic particles lose gt 99
of their energy ionizing gas, not inducing
nuclear reactions (Nath Biermann 1994) Consider
26Al 26Al / 27Al 5 x 10-5 implies 1045 26Al
atoms in a 0.01 M? disk Only 1048 particles
emitted in 1 Myr only 1047 intercept disk To
make a 26Al atom by 26Mg(p,n)26Al, a proton must
travel through ? 1.4 mH / (xMg26 ?) gt 3 x 106 g
cm-2 of gas But protons stopped by ltlt 10 g cm-2
of gas (Bethe formula) fewer than 1 proton in
105 reacts Even including other energetic
particles, other targets, cant make more than
1042 26Al atoms Similar results for other SLRs,
including 10Be
19
Irradiation inside the Suns Magnetosphere
very little gas -- its ionized and part of the
corona
e.g., X-wind model Shu et al. (2001)
only solids (CAIs) are irradiated
a fraction of the solids are returned to asteroid
belt
20
Seven problems with the X-wind model
  • Launching of solids from 0.1 AU to asteroid belt
    problematic winds probably launched from 1 AU,
    not 0.1 AU Coffey et al. (2004) trajectories
    very sensitive to particle size Shu et al.
    (1996)
  • CAIs formed in near-solar f O2, but reconnection
    ring is gt104 times more oxidizing than solar
    using values in Shu et al. (2001)
  • Concordant production of 26Al, 41Ca requires
    Fe,Mg silicate mantle to surround Ca,Al-rich
    core, but real minerals do not separate this way
    (e.g., Simon et al. 2002)
  • Production of 26Al or 41Ca at meteoritic levels
    will overproduce 10Be, using best-case scenario
    Gounelle et al. (2001) and new measured
    reaction rate for 3He(24Mg,p)26Al Fitoussi et
    al. (2004), especially if most 10Be is inherited
    Desch et al. (2004). See also Marhas
    Goswami (2004)

21
Seven problems with the X-wind model (continued)
  • Temperatures inside magnetosphere at least 750 K,
    and usually gt 1200 K Shu et al. (1996).
    Chlorine (including 36Cl) requires T lt 970 K
    to condense Lodders (2003)
  • Many other SLRs cannot be produced by spallation,
    including 60Fe, 107Pd and 182Hf Gounelle et al.
    (2001) Leya et al. (2003) and 63Ni Leya et al.
    (2003)
  • Siting of 26Al must be in small grains, not CAIs
    type 6 OCs heated to 1200 K, must have had
    abundant 26Al, yet OCs have almost no CAIs
    Ouellette Desch (2005, in prep)

Many of these problems pertain to any model of
irradiation in the Suns magnetosphere
22
Irradiation Conclusions
  • Energetic-particle irradiation occurs and can
    produce 10Be, 41Ca, 26Al, 53Mn, if irradiation
    occurs in Suns magnetosphere (to minimize
    ionization energy losses)
  • Confirmation of 7Be would demand irradiation
  • Concordant production of 41Ca, 26Al difficult,
    10Be probably overproduced, and 36Cl hard to
    condense
  • 60Fe, 107Pd, 182Hf (and 36Cl?) demand external
    source

23
Injection
Stellar nucleosynthesis products ejected by an
evolved star and enter the Solar System material
shortly before, or soon after, Solar System
formation
AGB star Contaminates Suns molecular cloud
(Wasserburg et al. 1994) Nearby
(Type II) Supernova Contaminates Suns molecular
cloud core and triggers its collapse (Cameron
Truran 1977) Injects into already-formed
protoplanetary disk...
24
AGB Star
Stars at least as massive as the Sun at the ends
of their lives enter Asymptotic-Giant Branch stage
SLRs created within star are dredged up to the
surface and ejected in a powerful wind
Eskimo nebula after AGB winds expose white dwarf
25
Problems with the AGB Scenario
  • AGB stars do produce 41Ca, 36Cl, 26Al, 60Fe,
    107Pd, 135Cs and 205Pb Wasserburg et al. 1994,
    1995, 1996, 1998 Gallino et al. 1998, 2004.
    But they do not produce 129I, 53Mn, or 182Hf.
  • AGB stars are extremely unlikely to be associated
    with the early Solar System. Kastner Myers
    (1994) conservatively calculate probability of
    contamination of Suns molecular cloud core at
    lt 3 x 10-6

26
Supernovae
  • Supernovae do produce all the confirmed SLRs
    41Ca, 36Cl, 26Al, 53Mn, 60Fe, 107Pd, 182Hf, 129I.
  • (Except for 10Be, which is known to have a
    separate origin.)
  • Relative abundances of SLRs in outermost 18 M?
    of a 25 M? supernova match meteoritic values very
    well Meyer et al. 2003
  • Order-of-magnitude agreement sufficient,
    considering real supernova ejecta highly
    heterogeneous

Cassiopeia A supernova remnant
27
time delay 0.9 Myr
Meyer et al (2003), LPSC abstract
28
time delay 0.9 Myr
Meyer et al (2003), LPSC abstract
29
time delay 0 Myr
Meyer et al (2003), LPSC abstract
30
time delay 0.4 Myr
Meyer et al (2003), LPSC abstract
31
Supernova and Star Formation
  • Meteoritic values require Solar System to be
    10-4 SN ejecta
  • Requires supernova lt 10 pc away, 1 Myr before
    CAIs formed
  • What are the odds our Solar System happened be
    near supernova? Like case of AGB star too low.
  • Supernova must be causally linked to Solar System
    formation perhaps the SN shock triggered the
    collapse of our cloud core Cameron (1963),
    Cameron Truran (1977) supernova trigger
    model

32
Supernova shock can inject right amounts of SLRs,
and trigger collapse of cloud core
if... Supernova shock can be slowed to 20 - 50
km/s Requires some intervening gas, travel times
t105 yr
Vanhala Boss (2002)
33
Problems with the Supernova Trigger Model
Environment in which supernovae occur is
important!!
low-density, ionized gas
dense molecular gas
n 10 cm-3
n 104 cm-3
cloud core
shocked gas
supernova progenitor
UV photons
ionization front
shock
0.2 pc
34
This gas already shocked no cloud cores
low-density, ionized gas
dense molecular gas
n 10 cm-3
n 104 cm-3
cloud core
shocked gas
supernova progenitor
UV photons
2 pc
ionization front
shock
? 0.03 g cm-2
35
supernova
ejecta
cloud core
shocked gas
2 pc
? 0.03 g cm-2
36
ejecta
?ej 10-4 g cm-2
cloud core
shocked gas
Vej 5000 km/s
2 pc
? 0.03 g cm-2
37
Ejecta transfers its momentum shock propagates
to cloud core, but is slowed to lt 20 km/s
cloud core
The actual ejecta (and SLRs) do not penetrate
into cloud they bounce! (Hester et al. 1994)
38
Injection  Conclusions
  • Injection by AGB stars highly unlikely, and
    cannot explain all isotopes anyway (esp. 53Mn,
    182Hf)
  • Injection by supernovae explains all isotopes
    well, but causal link to Solar System formation
    must be explained
  • Supernova trigger viable, but needed conditions
    may not exist where supernovae happen

39
Aerogel Model
Very close (lt 1 pc) supernova injected SLRs into
the Solar System, after it had formed a disk
?1 Ori C 40 M? O6 star will supernova in 1-2 Myr
Protostars with disks
Orion Nebula
40
When ?1 Ori C goes supernova, all the disks in
the Orion Nebula will be pelted with radioactive
ejecta Even more true for the disks observed in
Carina Nebula, with sixty O stars Smith et al.
(2003), many other H II regions Ejecta dust
grains penetrate disk, evaporate on entry, but
leave SLRs lodged in disk like aerogel Aerogel
Model
41
Potential Problems with the Aerogel Model
Q Wont the disks be destroyed by the supernova
shock? A No, disks are tightly bound to
protostar 30-AU disks gt 0.3 pc from
supernova definitely survive 10-AU disks gt
0.1 pc from supernova definitely survive
Chevalier (2000) Ouellette Desch (2004) Q
Isnt the disk too small for it to intercept
enough SLRs? A No,we are mixing only with 0.01
M? of disk material A 30-AU disk 0.15 pc
from a 25 M? supernova, or 0.4 pc .
from a 60 M? supernova ends up with 26Al/27Al
5x10-5
42
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43
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44
The special case of Nickel 63
Luck et al (2003) tentatively claim evidence for
live 63Ni (t1/2 101 yr) in the early Solar
System
Easily explained by aerogel model, since travel
times lt 100 yr
No other models can explain this result if live
63Ni is confirmed, its proof for the aerogel
model
45
Conclusions
  • Inheritance 10Be likely inherited (trapped
    cosmic rays), 129I may be inherited, but no
    others, especially not 60Fe!
  • Irradiation may be necessary for 7Be, but
    overproduces 10Be, cant explain 182Hf, 107Pd,
    (36Cl?), and especially 60Fe!
  • Injection AGB star cant explain 53Mn, 182Hf, is
    very unlikely supernova can explain all SLRs if
    link to Solar System formation made supernova
    trigger viable but may not pertain to real
    supernova environments
  • Aerogel Model Inevitable in supernova
    environments future modeling will test it 63Ni
    may prove it
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