Origins of the Short-Lived Radionuclides
and the Astrophysical Environment of
the Solar System’s Formation
Steve Desch
Arizona State University
Gordon Research Conference
Origins of Solar Systems
July 24, 2011
Isotopic analyses of meteorites reveal the onetime presence of many short-lived radionuclides:
10B
11Be
(Wadhwa et al. 2007)
41Ca
t1/2 = 0.10 Myr
41Ca/40Ca
=
10B
11Be
y = y0
≈ 1.5 x 10-8
0
+
10Be
9Be
+ m
x
9Be
11Be
x
Srinivasan et al. (1994; 1996)
36Cl
t1/2 = 0.30 Myr
36Cl/35Cl
≈ 5 - 17 x 10-6
Lin et al.(2005), Jacobsen et al.(2011)
26Al
10Be
t1/2 = 0.71 Myr
26Al/27Al
t1/2 = 1.51 Myr
10Be/9Be
≈ 5 x 10-5
Lee et al. (1976);
MacPherson et al. (1995)
≈
10-3
10B
11B
9Be
/ 11B
McKeegan et al. (2000), etc.
60Fe
t1/2 = 2.6 Myr
60Fe/56Fe
≈ 3 x 10-6
Tachibana & Huss (2003)
53Mn
t1/2 = 3.7 Myr
53Mn/55Mn
≈ 1 x 10-5
Lugmair & Shukolyukov (1998)
107Pd
182Hf
129I
t1/2 = 6.5 Myr
t1/2 = 8.9 Myr
t1/2 = 15.7 Myr
107Pd/108Pd
≈ 5-40 x 10-5
Chen & Wasserburg (1996);
Carlson180
& Hauri (2001) -4
182
Hf/
Hf ≈ 1 x 10
Kleine et al. (2002, 2005);
YinI/
et127
al.I(2002)
129
≈ 1 x 10-4
Swindle & Podosek (1998)
Multiple minerals within a single
inclusion (like this CAI), with
different Be/B ratios, are
measured
Isotopic analyses of meteorites reveal the one-time
presence of many short-lived radionuclides (SLRs):
(Wadhwa et al. 2007)
41Ca
t1/2 = 0.10 Myr
36Cl
t1/2 = 0.30 Myr
26Al
t1/2 = 0.71 Myr
10Be
t1/2 = 1.51 Myr
These 3 nuclei have 3 different origins
60Fe:
injection. Neutron-rich.
36Cl:
irradiation. Present only in late-stage alteration
Not produced significantly by
spallation; requires stellar nucleosynthesis. Only remotely likely
source is core collapse supernova(e). Levels consistent with
nearby supernova in same star-forming region.
60Fe
t1/2 = 2.6 Myr
products. Very short half-life. Levels too high too have been
injected by supernova or inherited from molecular cloud.
53Mn
t1/2 = 3.7 Myr
10Be:
107Pd
t1/2 = 6.5 Myr
182Hf
t1/2 = 8.9 Myr
including CAIs and hibonite grains, first to form. Ubiquitous and
uniform. Not produced by stellar nucleosynthesis. Levels
consistent with 10Be cosmic rays trapped in molecular cloud
(Desch et al. 2004), although this is debated (but keep watching).
129I
t1/2 = 15.7 Myr
inheritance. Present in a wide variety of samples,
107Pd, 182Hf, 129I,
probably inherited from ISM enriched in these SLRs
by long-term Galactic nucleosynthesis (Harper 1996; Jacobsen 2005).
Scenario #1: Desch et al. (2004); Ouellette et al.
(2005, 2007, 2009, 2010); Hester et al. (2004); Hester &
Desch (2005); Ellinger et al. (2009); Desch et al. (2010)
Galactic
cosmic rays
enrich ISM:
10Be
Irradiation at
several AU:
Radionuclides
inherited from
the molecular
cloud
36Cl, 53Mn?
Ongoing galactic
nucleosynthesis
enriches ISM:
129I, 182Hf, 107Pd
~ 1 local supernova injected
radionuclides into molecular
cloud or protoplanetary disk:
41Ca, 26Al, 60Fe, 53Mn?, 107Pd
Scenario #2: Shu et al. (1996, 1997, 2001);
Gounelle et al. (2001, 2006, 2009); Gounelle (2006);
Gounelle & Meibom (2007, 2008).
Irradiation at < 0.1
AU, followed by
outward transport
(X-wind):
41Ca, 36Cl, 26Al, 10Be,
53Mn
Radionuclides
inherited from
the molecular
cloud
Ongoing galactic
nucleosynthesis
enriches ISM:
~ dozens of local supernovae
injected radionuclides into Sun’s
molecular cloud ~15 Myr before
solar system forms (SPACE model):
129I, 182Hf, 107Pd, 53Mn?
60Fe, 53Mn?,
The SLRs 41Ca, 36Cl, 10Be, 26Al and 53Mn can be produced
in their observed proportions, incorporated into CAIs near
the Sun, then ejected to 2-3 AU, a la the X-wind model
(Gounelle et al. 2001). There is no need to invoke
supernova injection for these SLRs (Gounelle 2006).
The SLRs 41Ca, 36Cl, 10Be, 26Al and 53Mn can be produced
in their observed proportions, incorporated into CAIs near
the Sun, then ejected to 2-3 AU, a la the X-wind model
(Gounelle et al. 2001). There is no need to invoke
supernova injection for these SLRs (Gounelle 2006).
The X-wind can’t make CAIs, and can’t
produce those SLRs in the correct proportions.
They require some other origin, especially 60Fe
(Desch, Morris, Connolly & Boss 2010)!
The X-wind model
Shu et al. (1996, 2001)
HH30:
Krist et al.
(2000)
Desch et al. (2010) ApJ 725, 692, critiqued the X-wind model.
They found several problems.
Problem 1: Bipolar outflows often cited as support for X-winds, but observations show
outflows launched at 0.5-1 AU, not < 0.1 AU (Bacciotti et al. 2002; Anderson 2003; Coffey et al.
2004, 2007; Woitas et al. 2005). Disk winds carry > 70% of outflow (Woitas et al. 2005).
Problem 2: Observations show X point well inside where solids evaporate (Eisner et al.
2005).
Shu et al. (1996) estimated T < 1200 K at X-point because they neglected accretional
heating. With M > 2 x 10-7 M yr-1, T > 1440 K.
OOPS!
Problem 3: Solids do not fall out of funnel flow: they are entrained with gas all the way to
the star unless already > 4 mm in diameter. "Ad hoc" factor F=0.01 not at all justified.
Problem 4: If particles do fall out of funnel flow, their velocity relative to reconnection ring
will be ~ tens of km/s, enough to shatter particles in the disk.
Problem 5: Particles in reconnection ring feel dense, ~ 107 K plasma. Thermal sputtering
(neglected by Shu) prevents particle growth. CAI atoms remain gas, are swept into star.
Sputtering rate in 107 K plasma:
OOPS! Jones et al. (1996)
Problem 6: CAIs grow by recondensing rock vapor following big flares. Oxygen fugacity
fO2 > 105 x solar, inconsistent with CAI oxygen barometers like Ti+3/Ti+4 ratios in fassaite &
rhonite, and osbornite in CAIs (Beckett et al 1986; Krot et al. 2000; Meibom et al. 2007).
Shu et al. (2001)
Mg
"X-wind = eXtra oXidizing"
Ca,Al-bearing minerals in CAIs melt at lower T than
Fe,Mg-silicates. They don't form these structures!
Fe
O
Si
Ca
Al
O
Si
(Simon et al. 2002)
Problem 7: Energetic ions cannot produce 10Be, 26Al & 41Ca in right proportions. Ca does not
sequester itself in "refractory core", so 41Ca overproduced. 10Be overproduced relative to
41Ca and 26Al by factors > 3, especially if 10Be is trapped GCRs (Desch et al. 2004). And 60Fe is
underproduced by > 5 orders of magnitude (Leya et al. 2003; Gounelle 2006).
Problem 8: Magnetocentrifugal outflows only launch material from > 2 scale heights from
midplane (Wardle & Konigl 1993), but disk of CAIs & chondrules in reconnection ring < 1 / 25
times as thick. X-wind model doesn't explain lofting or calculate trajectories.
Bottom line: Protostellar jets don’t necessarily mean X winds, X winds don’t
make CAIs, and X winds don’t produce SLRs in right proportions.
10Be
can only be produced by irradiation, not by
supernovae. It may be a “smoking gun” for the
X-wind model (Gounelle et al. 2001; Gounelle 2006).
10Be
can only be produced by irradiation, not by
supernovae. It may be a “smoking gun” for the
X-wind model (Gounelle et al. 2001; Gounelle 2006).
10Be
has other sources, especially 10Be Galactic
cosmic rays trapped in our molecular cloud
(Desch et al. 2004). The X-wind actually
overproduces 10Be (Desch et al. 2004, 2010).
Galactic Cosmic Rays (GCRs) = nuclei of ions accelerated to relativistic speeds:
Mostly protons, ~10% alpha particles, heavier ions in roughly solar proportions.
The fluxes and energy spectra of GCRs, including 10Be nuclei, have been measured
by satellites (Webber et al. 2002; see Desch et al. 2004 and references therein).
10Be/H ratio is known… and is 106 x solar! (Spallations of ambient H on GCR O.)
GCR fluxes scale with supernova rate, therefore star formation rate, which was x2.2
higher 4.5 Gyr ago (see multiple references in Desch et al. 2004).
GCRs follow magnetic field lines, which
bend in regions of star formation.
Schleuning
et al. (1998)
Simulations by Desch & Mouschovias (2001) show how gas in a collapsing molecular cloud
core drags in magnetic field lines.
Magnetic field lines are
concentrated in core, focusing
GCRs inward.
High-pitch angle GCRs are
mirrored out of the cloud core.
High-energy GCRs pass through
the cloud core. Some cause
spallations of local O to form
10Be.
Low-energy 10Be GCRs are
stopped by ionizations and
trapped within the core.
Desch, Connolly & Srinivasan
(2004),ApJ 602, 528, calculated
the rates of all these processes
in a collapsing cloud core.
Desch and Mouschovias
(2001) and Desch et al.
(2004) calculate S(t) and
B(t) for different B fields.
30 μG collapses in 10 Myr,
5 μG collapses in 2 Myr.
10Be
GCRs
trapped in core
10Be
produced
by spallation
Total 10Be / 9Be
ratio.
Numerical error in
Desch et al (2004)
overestimated stopping rate by x3.
Should have found
10Be/9Be ≈ 6 x 10-4.
Bottom line: GCRs
provide molecular
cloud with right
amount of 10Be.
Additional sources
overproduce 10Be!
Final 10Be/9Be ratio very
insensitive to B field
because it saturates in
10Be half-life (1.5 Myr).
If 10Be comes from 10Be GCRs trapped in the
Sun’s molecular cloud, 10Be/9Be should be
uniform, but it’s not (Gounelle 2006).
If 10Be comes from 10Be GCRs trapped in the
Sun’s molecular cloud, 10Be/9Be should be
uniform, but it’s not (Gounelle 2006).
Yeah! We measured 5.3 ± 1.0 x 10-4 in
hibonites (Liu et al. 2009, 2010), which is
not consistent with 8.8 ± 0.6 x 10-4 in
Allende CAI 3529-41 (Chaussidon et al.
2006)!
If 10Be comes from 10Be GCRs trapped in the
Sun’s molecular cloud, 10Be/9Be should be
uniform, but it’s not (Gounelle 2006).
Yeah! We measured 5.3 ± 1.0 x 10-4 in
hibonites (Liu et al. 2009, 2010), which is
not consistent with 8.8 ± 0.6 x 10-4 in
Allende CAI 3529-41 (Chaussidon et al.
2006)!
Actually, 10Be is uniform. Not all
the data were analyzed correctly
(Desch, Ogliore, Morris & Huss 2011,
in prep)
MacPherson
et al. (2003)
10B
11Be
=
9Be/11B
10B
11Be
y = y0
0
+
10Be
9Be
+ m
x
9Be
11Be
x
Slope = 5.75 ± 1.90 x 10-4
χν2 = 0.85
10B
Goodness of fit tells you whether the
assumption of an isochron is valid!
11B
9Be
/ 11B
Chaussidon
et al. (2006)
10B
=
11Be
9Be/11B
10B
11Be
y = y0
0
+
10Be
9Be
+ m
x
9Be
11Be
x
The slope reported by Chaussidon et al. (2006),
8.8 ± 0.6 x 10-4, is incorrect, based on a wrong
equal fit of all data points.
Slope = 12.7 ± 0.78 x 10-4
χν2 = 29.8!!
10B
Isochrons are meaningless if you
can’t fit a line to the data!!
11B
9Be
/ 11B
Many points have 10B/11B > 0.25
Our interpretation:
B isotopes in
Allende 3529-41
reflect overall trend
of incorporating live
10Be, and variable
contamination by
spallogenic B
Spallogenic B has 10B/11B ~ 0.40
Chondritic ratio
Chaussidon et al. (2006)
10B/11B
= 0.248
Isochron cannot be
fit to the data.
Murchison
hibonites
Leoville, Vigarano, Efremovka CAIs
Axtel
l FUN
CAI
Allende
3529-41
Allende
CAIs
There are 17 analyses of 16 different samples. They all cluster around an average value.
Average value is close to 10Be/9Be ≈6 x 10-4.
Murchison
hibonites
Leoville, Vigarano, Efremovka CAIs
Axtel
l FUN
CAI
Allende
3529-41
Allende
CAIs
Eliminating the two analyses with the worst fits to an isochron (Axtell 2771 FUN CAI, χν2 = 4.4,
and Allende 3529-41, χν2 = 29.8) leaves 15 analyses with average 10Be/9Be = 6.3 x 10-4.
All other analyses have χν2 ≤ 2.2 and are consistent with average at 2 sigma level (except
Allende 3529-41, which is probably contaminated).
Bottom line: No evidence for 10Be heterogeneity!
There was also 7Be in the solar nebula, with
t1/2 = 53 days (Chaussidon et al. 2006)!
There was also 7Be in the solar nebula, with
t1/2 = 53 days (Chaussidon et al. 2006)!
That’s a smoking gun for irradiation in the
solar nebula (Chaussidon & Gounelle 2007)!
There was also 7Be in the solar nebula, with
t1/2 = 53 days (Chaussidon et al. 2006)!
That’s a smoking gun for irradiation in the
solar nebula (Chaussidon & Gounelle 2007)!
The evidence for 7Be was driven by model
assumptions and probably contamination by
spallogenic Li; there is no evidence for 7Be
(Desch & Ouellette 2006).
Chondritic ratio 7Li/6Li = 12.02
Many points have 7Li/6Li < < 12
Spallogenic Li has7Li/6Li ~ 2
The only evidence for live 7Be comes from the same CAI Allende 3529-41, analyzed by
Chaussidon et al. (2006), which is probably contaminated.
These data points are not the measured values; they have already been corrected for GCR
spallation within Allende. A better correction yields lower slope.
Best fit, done properly, is 7Li/6Li = (11.37 +/- 0.02) + (0.0092 +/- 0.0006) (9Be/6Li), χν2 = 17!!
Slope is driven entirely by points with 9Be/6Li < 30, with subchondritic Li ratios; eliminating
these yields fit 7Li/6Li = (11.80 +/- 0.07) + (0.0010 +/- 0.0012) (9Be/6Li), χν2 = 0.72.
Bottom line: We interpret all variability in 7Li/6Li due to contamination, not 7Be.
It’s not possible to inject 36Cl from a supernova
along with 26Al and 41Ca, its levels are too high
(Gounelle 2006; Jacobsen et al. 2011). 36Cl must be
formed in the solar nebula.
It’s not possible to inject 36Cl from a supernova
along with 26Al and 41Ca, its levels are too high
(Gounelle 2006; Jacobsen et al. 2011). 36Cl must be
formed in the solar nebula.
Yes, 36Cl must be produced in the solar
nebula, but not in an X-wind (Desch et al.
2010). It probably formed by irradiation of ices
in the disk during the transition disk stage
(Jacobsen et al. 2011; Desch et al. 2011, in prep).
Evidence for 36Cl found only in late-stage aqueous alteration
products like sodalite (Lin et al. 2005) and wadalite (Matzel et al.
2010; Jacobsen et al. 2011), at levels up to 36Cl/35Cl ~ 1.7 x 10-5.
Al-Mg age of wadalite is 2.6 Myr after CAIs. Injecting 36Cl
and 26Al from same supernova requires 36Cl/35Cl ~ 7 x 10-3,
higher than any supernova models predict.
36Cl
must be produced by irradiation, but X-wind region is
too hot for 36Cl or its targets (S, Cl, Ar, K) to condense.
Irradiation must take place further out in disk.
Courtesy Sasha Krot
Jacobsen et al. (2011; ApJ) hypothesize irradiation of ices at a few AU in late stage of disk in
which gas had thinned, followed by accretion of ices by carbonaceous chondrite parent
bodies; predicted that (additional) 10Be should accompany 36Cl.
Desch et al. (2011; LPSC) also hypothesize irradiation of ices in transition disk stage, predict
spallogenic Li and B, and maybe 53Mn, should accompany 36Cl.
Spitzer observations show 10-20% of observed disks are transitions disks like TW Hydrae
and DM Tau (Williams & Cieza 2011). Disks probably spend 0.5 – 1 Myr in this stage, at ages
3-6 Myr.
Column densities ~ 1 g cm-2, optically thin to energetic ions.
Desch, Krot, Alexander & Allu Peddinti (2011; LPSC) modeled isotope production in
transition disk, including new reaction 38Ar(p,ppn)36Cl. Very little mass is irradiated, but
that which is sees no dilution.
Preliminary
Predictions:
36Cl/35Cl = 3 x 10-6
7Li/6Li = 9.2
53Mn/55Mn =2 x 10-5
10Be/9Be ~ 0.007
Of these, Cl, Li, Mn
mobilized;10Be will
precipitate before
reaching interior
Bottom Line:
Late irradiation in
a transition disk
may explain 36Cl,
as well as B and
Li anomalies.
Injection of 60Fe, 26Al and 41Ca into our
protoplanetary disk would have noticeably altered
the oxygen isotopic composition of the disk
(Gounelle and Meibom 2007).
Injection of 60Fe, 26Al and 41Ca into our
protoplanetary disk would have noticeably altered
the oxygen isotopic composition of the disk
(Gounelle and Meibom 2007).
If only supernova dust is injected, this is no
problem at all (Ellinger et al. 2010).
Ouellette et al. (2005, 2007, 2010) advanced
the “aerogel” model in which ejecta are
injected directly into the protoplanetary disk
as dust grains.
Ouellette et al. (2007) showed gas-phase
ejecta are not injected (< 1% efficiency).
Ouellette et al. (2010) showed that large
supernova dust grains (diameters > 100 nm)
are injected efficiently (up to 90%).
If only condensible dust is injected, oxygen isotopic shifts are
small.
Corundum (Al2O3) grains only have
M(26Al)/M(16O) = 1.08.
If all 26Al is in corundum grains and
only corundum grains are injected,
Injection of dust alone leads to isotopic
shifts << 1 permil, too small to be noticed. isotopic shifts < 0.001 per mil.
Fraction of supernova ejecta that condenses into dust is hotly debated, as reviewed
in Ouellette, Desch & Hester (2010) ApJ 711, 597.
Observations of dust in high-z galaxies imply 0.1 – 1 M of dust per supernova
(Morgan & Edmunds 2003).
Dust in SN1987A formed ~ 2 years after explosion; only 10-4 M directly seen in IR.
But emission was from optically thick (at 30 μm) clumps (Wooden et al. 1993).
Ouellette et al. (2010) argued most supernova observations miss dust because it is in
clumps, and SN1987A could have held up to 1 M of dust.
Recent Herschel observations (Matsuura et al. 2011) have revealed 0.4 - 0.7 M of cold
(T = 20 K) dust in SN 1987A, implying condensation efficiency ~ 30 – 60%
In these clump
models, P reaches
10-4 bar, 103 times
higher than
previously
considered
Fedkin et al. (2010)
Many models (e.g., Kozasa et al. 2010) predict high condensation efficiencies, but
still predict unobserved features, because they have ignored clumpiness.
Ouellette et al. (2010) presented a model for P-T conditions in clumpy ejecta.
P ≤ 10-6 bar
yields graphite
condensing
before SiC,
FeSi, metal…
Clumpy ejecta
pressures
P ≥ 10-5 bar
yields TiC, then
SiC / FeSi /
metal, then
graphite.
Same sequence
observed by
Croat et al.
(2011 LPSC) in
an Orgueil SN
Fedkin et al. (2010)
presolar grain!!
Strong evidence that SN presolar grains condensed in clumps. Clumps enhance
dust growth and hide dust emission… suggests supernova dust condenses more
efficiently than thought.
Meteorites and planetary materials have 54Cr anomalies due to incorporating
different proportions of some 54Cr carrier (Qin et al 2010; Trinquier et al 2007).
This carrier just discovered: presolar “nanospinels” < 100 nm in size, with
54Cr/52Cr 3.6 x solar (Dauphas et al. 2011), some up to 50 x solar (Qin et al. 2011).
Must have been formed in a supernova. Dauphas et al. (2011), Qin et al. (2011)
argues for late injection of these presolar grains.
Larsen et al. (2011) find correlation between 54Cr anomalies and 26Mg
excesses… nanospinels may also be the carrier of 26Al!
Bottom line: Supernovae make abundant (~ 0.5 M) dust;
at least half of condensible material condenses into dust.
~50% of 100nm dust can be injected into a protoplanetary disk (Ouellette et al. 2010).
Relatively high percentage of 26Al and 60Fe, etc., can be injected as dust into disk.
Injection of dust without gas will not significantly alter oxygen isotopic composition
of solar nebula (Ellinger et al. 2010).
But SLRs in CAIs like 26Al and 41Ca must be
formed in situ... it’s not possible to inject SLRs
from a supernova, within the first < 1 Myr, at the
required levels (Gounelle and Meibom 2008).
But SLRs in CAIs like 26Al and 41Ca must be
formed in situ... it’s not possible to inject SLRs
from a supernova, within the first < 1 Myr, at the
required levels (Gounelle and Meibom 2008).
And we know 60Fe
requires a supernova
origin.
It is possible, with triggered star formation
and clumpy supernova ejecta. Injection into
disk has ~1% probability (Ouellette et al. 2010).
Injection into molecular cloud also works and
is likely (Pan et al. 2011, in prep).
HST/K.Luhman
Simple geometric arguments show that disk must be < 0.15 pc from (isotropically
exploding) supernova to get 26Al/27Al > 5 x 10-5 (Ouellette et al. 2005; Looney et al. 2006).
Thousands of protostars with disks lie < few x 0.1 pc from O stars in Orion Nebula…
… but that star won’t explode for > 4 Myr. By the time it does, coevally formed disks won’t
be young disks anymore!
Some disks do lie
< 1 pc from stars
< 1 Myr from
exploding, but
they’re rare.
Still, H II regions
like NGC 6357
provide evidence
for triggered star
formation.
O3If* star Pismis 24,
already evolved off
main sequence
NGC 6357:
Healy et al. (2004)
O stars’ UV drives
ionization fronts and
shocks into molecular
cloud, triggering star
formation.
Hester & Desch (2005)
Combined Spitzer / HST survey of 2-Myr-old region NGC 2467 (Snider et al. 2009) and other H II
regions (Snider PhD thesis, 2008) show protostars continue to form many Myr after O stars, and
their locations are highly correlated with ionization fronts, indicating a triggered formation.
Triggered star formation continues until most massive stars go supernova.
Easily 30-50% of
low-mass stars
in H II regions
are triggered by
massive stars.
~ 10% form just
< 1 Myr before
supernova.
NGC 2467:
Snider et al. (2009)
The problem is these
disks are far from the O
star.
Ionization fronts
advance ~ 0.5 – 1 km/s
= 2 – 4 pc in 4 Myr.
Stars that do form just
before supernova are
far away (>2 pc).
Isotropic supernova
ejecta too diluted to
explain 26Al/27Al ratio
(by a factor ~ 300).
> 2 pc!
Hester & Desch (2005)
4 pc
But
supernovae
are NOT
isotropic!
Cassiopeia A, 300-year-old supernova remnant
(X ray = NASA Chandra, optical = NASA HST; infrared = JPL)
HST: Fesen
& Morse
At d ~ 2 pc from explosion center, HST resolves thousands of knots, each ~ 10-4 M,
each ~ 0.1 – 1” (~ 1016 cm), probably formed by R-T instabilities during explosion.
N ~ 3000 bullets of mass ~ 3 x 10-4 M each, expanding homologously with
radius R = d / 300 (consistent with numerical simulations and observed
clumps in SN1987A and Cas A) have filling fraction N πR2 / (4πd2) ~ 0.8%
Only 0.8% of disks receive ejecta, but those that do get 120 times what
they’d get if ejecta were isotropic, equivalent to being 11x closer.
Bottom line: Disks at 2 pc can form and within 1 Myr receive sufficient
ejecta to explain 26Al and 60Fe abundances… but only 0.1 - 1% of disks in
H II region conform to this scenario.
(But multiple supernovae may ameliorate problem somewhat)
And the fact remains… 60Fe requires a supernova origin!
Supernova bullet
These same bullets colliding with
the surrounding molecular cloud
penetrate about 0.5 pc before
stopping and mixing with cloud gas
in channel with area ~ 0.02 pc2.
Cloud area per bullet ~ 0.02 pc2.
All molecular cloud cores on verge
of collapse will be mixed with one
~10-4 M bullet of supernova ejecta
from some zone in the progenitor.
Multiple (~ 10) supernovae in H II
region may lead each star to be
mixed with ~10-3 M of supernova
ejecta from ~10 zones in different
supernovae. Work in progress.
This may be how supernovae
delivered 60Fe to solar system.
2-D Flash simulations by Pan, Scannapieco,
Desch & Timmes (2011, in prep)
60Fe
does require a supernova origin, but not a
single nearby supernova. Contamination of the
molecular cloud by dozens of supernovae over
the previous 15 Myr (SPACE model) is sufficient
(Gounelle et al. 2009).
60Fe
does require a supernova origin, but not a
single nearby supernova. Contamination of the
molecular cloud by dozens of supernovae over
the previous 15 Myr (SPACE model) is sufficient
(Gounelle et al. 2009).
The SPACE model overestimates the
efficiency by which 60Fe is mixed into
molecular clouds (Desch et al. 2010). And it
overpredicts the 53Mn / 60Fe ratio by orders
of magnitude!
Lowdensity
ISM
Gounelle et al. (2009),
SPACE (Supernova
Propagation and Cloud
Enhancement) model
Molecular cloud 1
has ~ 3000 M,
Molecular cloud 2
has ~ 8000 M
Shocks from cloud 1
can’t cause
contraction of a
new molecular
cloud 15 Myr later
unless gas can cool.
To get 60Fe/56Fe ~ 10-6 …this gas must be swept …to form new
…and 60Fe mixed in
in forming system…
up and compressed…
molecular clouds… with 100% efficiency
This low-density gas is heated when shocked and can’t cool and compress… SPACE relies on
a thermal instability to cool (Koyama & Inutsuka 2002; Audit & Hennebelle 2010) that works at
shock speeds < 100 km/s and T < 104 K, not the 2000 km/s shock speeds and 107 K gas here.
A problem recognized by Gounelle et al. (2009): supernovae produce too much 53Mn
along with 60Fe.
60Fe
produced in innermost 6 M, 53Mn in innermost 3 M.
If all of the ejecta are mixed, 53Mn / 60Fe ~ 102 x higher than meteoritic ratio
For a single supernova may not eject all its material: progenitors > 20 M often
experience “fallback” of innermost few M (Umeda & Nomoto 2002, 2005; Nomoto et al.
2006; Tominaga et al. 2007), resolving the 53Mn / 60Fe problem (Takigawa et al. 2008).
A disk or molecular cloud may receive a clump of supernova ejecta from one zone in
the progenitor.
SPACE model invokes 4-22 (average 12) supernovae and mixes all of their ejecta.
They can’t all experience fallback.
Bottom line: not clear how formation of new molecular clouds are triggered by
massive stars; not clear how 60Fe is mixed into new clouds; not clear how to avoid
mixing in too much 53Mn.
Short-lived radionuclides are important probes of
the Solar System’s formation environment.
Multiple SLR origins are needed.
36Cl formed by irradiation in solar nebula.
60Fe came from 1 or dozens “nearby” and
“recent” supernova(e).
Conclusion: Scenario #1!
1. Sun’s molecular cloud already enriched with 107Pd,
182Hf, 129I… as it collapses, 10Be GCRs trapped in it.
2. Massive stars’ ionization fronts
trigger formation of low-mass
stars, including Sun.
3. Supernova injects 26Al, 41Ca,
53Mn, 60Fe into disk or cloud.
4. Irradiation in Sun’s transition disk,
~ 3 Myr later, creates 36Cl, spallogenic
Li & B, maybe some 53Mn.