Download The Local Bubble

The Local Bubble
Michael M. Schulreich
Zentrum für Astronomie und Astrophysik
Technische Universität Berlin
Superbubbles, HI holes and Supershells
10/11/2014
Title image: Volume rendering of the simulated density
distribution connected to the Local and Loop I superbubble
(background ISM was assumed to be homogeneous)
The Local Bubble and its Origin
The discovery of the Local Bubble
1968)
• Color excess measurements (Fitzgerald
Cavity of
thin hot gas in
-
the local interstellar
Hole in interstellar dust around themedium
Sun
Extension in Galactic plane: ~ 50 Extensions:
× 100pc
200 pc in the
Sounding rocket flights in the 1980s (e.g.
Univ. of
Galactic
Plane
Wisconsin Survey; Mc Cammon & Sanders
6001990);
pc perpendicular
mapped diffuse soft X-ray (SXR) emission from a large
Produced by 14 - 20
fraction of the sky
supernova explosions
starting ⇠14 Myr ago
bands
- No strong intensity variations of ultra-SXR
(Fuchs
et
al. 2006)
(E ≤ 0.3keV) on large angular scales (Bloch et al. 1986)
Subgroups
Upper
Lupus
➔ SXR emitting plasma must contained
in Centaurus
cavity
(UCL) and
Lower
Centaurus
Crux
Lyman α absorption measurements
in the
spectra of
nearby hot stars
(LCC) of the Scorpius
Centaurus Association
- HI deficient in the local ISM
-
•
•
Jenny Feige, DPG 2014
Detecting SN Dust on the Earth’s Sea Floor with AMS
7 / 12
Anti-correlation ➔ „displacement model“ (Sanders et al. 1977; Snowden et al. 1991)
•
•
Solar system resides in a cavity filled with hot plasma that locally displaces HI gas as far as 100pc
Actual SXR emitting volume has even greater extent toward the Galactic poles since observed photon flux increased
from plane to pole by a factor of 2 to 3
Michael Schulreich
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
The discovery of the Local Bubble
Further constraints for the Local Bubble‘s (LB) dimensions ...
(l=90) (y)
(pc)
200
NGP (z)
(pc) NGP (z)
200
200
(pc)
100
100
100
GC (l=0) (x)
GC (l=0) (x)
(l=90) (y)
-200
(pc)
-100
0
0
0
0
100
-200
200
-100
0
100
-200
200
-100
0
100
200(pc)
(pc)
-100
-100
-100
-200
-200
-200
(c)
(b)
(a)
Sfeir et al. (1999)
... from observing equivalent width of NaI lines toward
hundreds of stars with known Hipparcos parallaxes (Sfeir
et al. 1999, Lallement et al. 2003):
• Bubble is asymmetrically shaped and tilted about
•
•
20° to the direction of the Galactic poles
Radius varies between ~60 and 250 pc within the
Galactic plane
Generally elongated in vertical direction; possibly
open-ended toward Galactic north pole (chimney?;
Welsh et al. 1999)
... from shadowing experiments based on ROSAT data:
• Dense absorber (molecular cloud) at known distance
•
•
allows to separate foreground from background
emission
Determination of emission measure and thus electron
density in the foreground
Derivation of bubble extension in different directions
(assuming homogeneous density and temperature in
bubble interior; Snowden et al. 1998)
Cavity and LB are not the same in all directions
➔ LB might contain some warm rather than hot gas, and/or is inhomogeneous
Michael Schulreich
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
The discovery of the Local Bubble
L. Puspitarini et al.: Local ISM 3D distribution and soft X-ray background
recycling
under the action
of higher
stellar winds
and supernova
(SN)
More extended
and
resolved
maps
of the local ISM
explosions that inflate hot MK bubbles within dense clouds.
(Lallement etmodels
al. 2014)
Hydrodynamical
of the multi-phase ISM evolution under the action of stellar winds and supernova remnants (SNRs,
inverting
~23,000
redding
measurements toward
e.g., Created
de Avillez from
& Breitschwerdt
2009)
demonstrate
how high
density
and temperature
nearby
stars contrasts are maintained as shells are
cooling and condense over the following thousand to million
years,
giving birth
to new of
stars.
Clouds
engulfed
by expanding length (structures smaller
Limited
number
target
stars
➔ smoothing
hot gas evaporate. However, depending on their sizes and densithanmay
15survive
pc are
mapped
atcavities.
their actual
sizes)
ties they
up not
to Myrs
in the hot
This is the
case for the LB: as a matter of fact, beside hot gas, cooler clouds
Black
line:areROSAT
unabsorbed
0.25keV
surface brightness
(∼5−10
pc wide)
also present
inside the bubble,
including
a group
of very tenuous
within 10−20 parsecs from the
(Snowden
et al.clouds
1998)
Sun, the Local Fluff.
6
Hot
gas line:
(T ∼ 10averaged
K) emits soft
X-rays and heliospheric
produces a back- contribution to the signal
Blue
estimated
ground that has been well observed during the ROSAT survey
(Puspitarini
al. 2014)
(Snowden
et al. 1995,et1997).
The 106 K gas is primarily traced in
the 0.25 keV band, while hotter areas appear as distinct enhancements in the 0.75 keV maps, whose sources are supernova remnants, young stellar bubbles or super-bubbles (Snowden et al.
1998). In the softer bands a fraction of the X-ray emission is
generated in the Galactic halo, and there is also an extragalactic
Fig.
1.
Differential
color
excess
in
the
Galactic
plane,
derived
by
inverLong standing debate:
contribution.
sion of LOS data (map taken from Lallement et al. 2014). The Sun
With the assumption that the Local Bubble and other nearby
is at (0,0) and the Galactic center direction is to the right. Cavities (in
Is the
SXR background
duearetofilled
thewith
LBhotatgas.
all,A or
due
to ISM are filled with hot gas, then in principle
cavities
in the
red)
are potential
SXRB sources if they
po-rather
lar
plot of the
unabsorbed (foreground)
0.25between
keV diffuse background
charge
exchange
reactions
solar windknowledge
ions andof the 3D geometry of the ISM may be used to synderived from shadowing (Snowden 1998a) is shown superimposed in thesize SXRB intensity distributions (maps), as well as spectral
interstellar
intoscaling
the heliosphere?
black
(thick line),neutrals
centered on streaming
the Sun. The linear
of the X-ray information to compare with observations. This can be done by
surface brightness, i.e., the ratio between surface brightnesses and par- computing the X-ray emission from all empty (low density) reetconsistent
al. (2014)
analyzed
theof helium
secs,Galeazzi
is chosen to be
with the
physical extent
the LB. Alsofocossing
gions, and cone
absorption by any matter between the emitting reshown is the shape of the estimated average heliospheric contribution gion and the Sun. Provided maps and data are precise enough,
(abundant of neutral gas ➔ ideal place for probing solar wind‘s
to the signal (dashed blue line). This contribution has been arbitrarily it should be possible to derive the pressure of the hot gas as a
X-ray
efficiency)
scaled
to makeproduction
it more visible and
the heliospheric signal should not be
function of direction and partly of distance. This is what we illusdirectly compared here with the measured background.
trate here, in a simplified manner, using only the X-ray surface
Found that both sources are required to produce
0.25This
keV
brightness.
work will be updated and improved as higherflux in
Galactic
(40%
solar wind;
60%resolution
hot LB3D
gas)
maps become available.
examples
of the
potential
studies plane
based on
the combination
of 3D
Figure 1 shows the large-scale structure of the local ISM as
maps and diffuse X-ray emission.
➔ Bold
ofquestions
the thepreviously
LB‘s existence!
Image: NASA's Goddard Space Flight Center
We
addressconfirmation
in particular the two
men- it comes from the inversion of stellar light reddening measurements.
About
23
000
color
excess
measurements
based
on
the
tioned: (i) we compare the shapes and sizes of the nearby cavities with the soft X-ray data, in a search for properties of the Strömgren, Geneva and Geneva-Copenhagen photometric syshave been assembled for target stars located
at distances
Michaelhot
Schulreich
Localtems
Bubble
Superbubbles,
HI holes and Supershells - 10/11/2014
nearby
gas; (ii) we search a potential source region The
for the
•
•
•
•
•
•
The origin of the Local Bubble
• Product of local SN explosions (e.g. Cox & Smith 2001)
• „Smoking gun“ is difficult to find as present LB territory lacks
an OB association that might have harbored SN precursors
• Berghöfer & Breitschwerdt (2002) searched for a moving group
that had passed through solar neighborhood in the past
➔ Pleiades subgroup B1 (its present day stars are members of
the Sco Cen association)
• Fuchs et al. (2006) scrutinized complete volume (Ø 400 pc)
centered at the solar system in the Hipparcos and ARIVEL
catalogue
• Selected only those 79 B stars that are concentrated in both
real and velocity space
Fuchs et al. (2006)
• Extrapolated trajectories (center of mass) back in space & time
• Using initial mass function (IMF) ➔ number of SNe in the past; explosion sites (from trajectories); explosion
times (from MS life times; assuming that stars in cluster are born coevally)
• Cluster age: put de-reddened cluster stars into CMD; turn-off point from isochrones (Schaller 1992)
• Association had entered present LB volume rather off-center 10 to 15 Myr ago
• Since then, 14 to 20 SN explosions should have occured (last explosion only ~0.5 Myr ago)
• Corresponding energy input into surrounding ISM is consistent with current LB size
Michael Schulreich
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
Local Bubble simulations
First, provide ,realistic‘ (SN-driven) background ISM for LB evolution calculations
• EVAF: 3D parallelized adaptive mesh refinement (AMR) hydrocode [details in de Avillez & Breitschwerdt (2004, 2005)]
• Solves full HD/MHD equations on large domain: 1 kpc × 1 kpc × ±10 kpc
• Boundary conditions: periodic (four vertical boundary faces); outflow (top & bottom boundary)
• Type Ia,b,c/II SNe random + clustered in disk
• Background heating due to diffuse UV photon field
• Gravitational field by stars + self-gravity
• SFR
local density/temp.: n > 10 cm-3 / T ≤ 100K
➔ Formation and motion of OB associations (random velocity of stars)
• Evolution of computational volume for τ ~ 400 Myr
➔ Sufficiently long to erase memory of initial conditions
Michael Schulreich
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
HD-Evolution of ISM II
Avillez & Breitschwerdt, 2010
Results
Local Bubble simulations
x
Collective effect of SNe induces
Self-consistently evolved ISM break-out
features ...of ISM disk gas ➔ “galactic fountain” (cf. intermediate velGalactic fountain flow due toocity
SN-induced
break-out
of ISM
clouds) ➔
reduce disk
pressure y
✤
disk gas
Density and temperature distribution shows structures on all scales
structures on all scales in density and temperature distribution
(cf. observation of filaments)
✤
shear flow due to expanding
SNRsflow
(generate
level of SNRs
shear
due tohigh
expanding
turbulence ➔ coupling of scales)
generate high level of turbulence ➔
coupling of scales
cloud formation by shock compressed
layers ➔ clouds are
✤
Cloud formation by shock comprestransient features ➔ generation of new stars
sed layers ➔ clouds are transient
features
➔ generation
large amount of gas in thermally
unstable
phases of new stars
✤
large amount of gas in thermally
volume filling factor of HIM ~20%
unstable phases
HIM ~ 20%
no pressure equilibrium! ✤ volume filling
de factor
Avillez &of
Breitschwerdt
(2010)
✤
no pressure equilibrium!
✤
•
•
•
•
•
•
•
Dieter Breitschwerdt - Workshop on “Magnetic Fields on scales from kpc to km” - Cracow, 18.5.2010
ROSAT PSPC observations (Egger & Aschenbach 1995)
Wednesday, June 9, 2010
• SXRs absorbed by nearby neutral shell
• Possibly the result of an interaction between the LB
shell
Loop I superbubble
ring
and its neighboring SB Loop I (Breitschwerdt et al.
2000)
0
17
LIC
• Loop I excited by the Sco Cen association, or one of its
distinct subgroups
pc
Sco-Cen
association
wall
Sun
galactic plane
HI clouds
Local Bubble
➔ Study joint evolution of LB & Loop I
Michael Schulreich
The Local Bubble
shell
ring
Superbubbles, HI holes and Supershells - 10/11/2014
Local Bubble simulations
D. Breitschwerdt et al.
our-coded
p in the range
for a slice
cube
e Galactic
D LB
simulation
present time (i.e.
he first explosion)
tred at (175,
p I shifted
ht. Bottom:
the “future” of
p I at
ote that part of
ged with the ISM,
gulfed by Loop I
Breitschwerdt
006)
Breitschwerdt et al. (2009)
• SBs are generated almost coevally cooler (OVI absorbing) and hotter (X-ray emitting) gas co-exist. This is a direct result of
the turbulent and inhomogeneous density and temperature structure in realistically evolved
structure
superbubbles.
Turbulent mixing generates gas in the whole thermally unstable regime be• In the beginning: smooth and spherical
tween 10 –10 K. While the amount of OVI in the LB has been measured fairly accurately
MyrSect.
of evolution
due
to inhomogeneous
medium
3), the source
of the
soft X-ray emission isambient
more elusive.
First of all, it is more dif• Develop internal structures after ~8(see
ficult to localize, as there are most likely no dense clouds inside the LB, which can be used
instability
for shadowing
experiments, thus allowing us to separate back- and foreground emission.
• Interacting shells develop Rayleigh-Taylor
Secondly, an as yet uncertain amount of soft X-rays will be produced locally by solar wind
• Instability becomes non-linear ➔ Formation of Local Cloud and its companion HI clouds (cf. Breitschwerdt et al. 2000)
• Two bubbles will merge in ~3 Myr from now, when interaction shell starts to fragment
5
Michael Schulreich
6
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
The OVI test: Comparison with FUSE and Copernicus data
Turbulence inside SBs: cooler (OVI
absorbing) and hotter (X-ray emitting) gas
can coexist
Averaged OVI column density vs. LOS path length for simulated LB/
Loop I (14.3 ≤ t ≤ 14.7 Myr)
• Steep decrease after
Comparison of FUSE data with simulated
minimum, maximum, and averaged OVI
column densities (91 LOS between ±45°)
last SN in LB (no further
heating)
• For
>100pc:
⟨N(OVI)⟩ > 2 × 1013cm-2
LOS
Histograms of the percentage of LOS vs. log N(OVI) in simulated LB
at t=14.5 and 14.6Myr
• Max[⟨N(OVI)⟩]
=1.78 × 1013 cm-2
• Copernicus absorption
line data: 1.6 × 1013cm-2
(Shelton & Cox 1994)
➔ Pin down LB age: ~14.5 Myr
Michael Schulreich
Breitschwerdt et al. (2009)
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
Relics of the ,Blast from the Past‘
of a massive star close to the solar system
A Crust from the Pacific Ocean
Validate LB evolution models ➔ Search for
traces of involved SNe on Earth
Promising tracer: Radionuclide 60Fe
Crust description
Produced inside massive stars via
successive neutron
capture
on other Fe
Fe-Mn
Crust
isotopes, both before and during the SN
Depth: 4380 m
explosion
Growthon
rate:
No in-situ production
Earth
2.37 life
mm/Myr
Comparatively long
time (t1/2 = 2.6 Myr)
he
in
nity
•
will
t in
o
Courtesy of TU Munich
Jenny Feige, DPG 2014
A Crust
from the Pacific Ocean
•
A Crust• from the Pacific Ocean
Detecting SN Dust on the Earth’s Sea Floor with AMS
3 / 12
Ferromanganes
crusts
Target
Isotope: 60 Fe
~20% Mn
and ~15%
Fe
Crust
description
t1/2 = 2.6and
Myr-plateaus,
Crustondescription
Found
sea-mountains
Fe-Mn
Crust
deep-sea volcanoes
and
the
mid-ocean
No in-situ
production
Crust 4380 m
ridges Fe-Mn Depth:
on Earth
4380
mrate: from ambient
Obtain Depth:
elemental
composition
Growth
water Procedure:
Growth2.37
rate:mm/Myr
Low growth
(< 10 mm/Myr)
2.37rate
mm/Myr
Cutting
pieces 60
of
Target
Isotope: Fe
Specific crust
237KD
2 mm
60
Target
Isotope:
Fe ever
One of the biggest Fe-Mn crusts
tTime
2.6 Myr
1/2 = information:
recovered
t1/2 = 2.6
Myr
400000
yrproduction
in 1 mm
No
in-situ
Stems from North Equatorial Pacific
No 2in-situ
production
Measurement
on
Earth
Sliced into
mm
thick
pieces with
on Earth
Accelerator
Mass
Time information:
400,000
yr
in
1 mm
Procedure:
Spectrometry
Measurement
with Accelerator Mass
Procedure:
Spectrometry Cutting pieces of
Jenny
•
•
•
•
•
•
•
•
•
Cutting pieces of Detecting SN Dust on the Earth’s Sea Floor with AMS 4 / 12
2 mm
The Local
Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
Time information:
2 mm
Jenny Feige, DPG
2014
Michael Schulreich
10
New
Be Dating ofvs.
theMeasurements
Crust
Analytical Calculation
Relics of the ,Blast
from
the
Past‘
The peak
shifts
from
2.8 - 2.2 Myr
An enhanced concentration of 60Fe was measured in 237KD
by Knie et al. (2004) and confirmed by Fitoussi et al. (2008)
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➔ 60Fe amount deposited on Earth by arriving SN blast waves
➔ Good agreement with crust measurements
Michael Schulreich
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The LB and the Fe Anomaly in the Ocean’s Crust
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blue, LCC: red) plotted over the 60 Fe measurements (black
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The 60 Fe/Fe ratio versus the age of the crust based
on the new 10 Be dating.
3
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Superbubbles, HI holes and Supershells - 10/11/2014
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Crust
Analytical Calculation
Relics of the ,Blast
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the
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The peak
shifts
from
2.8 - 2.2 Myr
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points) with an ISM dens
The 60 Fe/Fe ratio versus the age of the crust based
on the new 10 Be dating.
3
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➔ Perform 3D high-resolution numerical simulations
The Local Bubble
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The LB and the 60 Fe Anomaly in the
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2007
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Superbubbles, HI holes and Supershells - 10/11/2014
RAMSES: a parallel graded octree AMR hydrodynamics code
• Code developed by Teyssier (2002)
• Freely available for download online
• Tree-based AMR (octree structure):
•
•
Cartesian mesh is recursively refined
on cell-by-cell basis
Fully threaded: each oct has direct
access to neighboring parent cells
and children octs ➔ Optimized mesh
adaption to complex geometries
MPI-based parallel implementation ➔
Space filling curves
• Hydro module: Unsplit second-order
•
•
•
•
Godunov method ➔ Riemann solver
with piecewise linear reconstruction
(MUSCL-Hancock scheme)
MHD module: Constrained transport
scheme
RHD module: GPU-accelerated
(CUDA libraries); grey flux-limited
diffusion approximation
N body module: Particle-mesh
method on AMR grids; efficient
Poisson solvers
Additional physical modules mainly
tailored for cosmological applications
Modified and extended RAMSES to recreate previously described ISM setup:
Star formation (IMF; collisionless particles represent massive stars)
Feedback from stellar winds and SNe
Solar wind bubble
Self-gravity of the gas & external gravitational field (bulge, disk, halo contribution)
Heating & CIE cooling for gas with solar metallicity
Stellar trajectories (provided by Ch. Dettbarn, ARI): UCL/LCC (Sco Cen subgroups)
- Take errors in Hipparcos data into account
- Drop assumption of center of mass motion for all SN precursors
- Use Gaussian error distribution for stellar paths
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Michael Schulreich
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
Evolution of the local interstellar medium over 246 Myr
Michael Schulreich
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
Calculating the amount of SN-released 60Fe that arrives on Earth
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Spatiotemporal evolution of the concentration of 60Fe (chemical mixing) is treated as advectiondiffusion process of a passive scalar
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Includes radioactive decay of 60Fe based on the latest half-life data
• Force maximum grid refinement at the center of the computational box (locus
of the solar system ➔ allow for accurate 60Fe flux measurements
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As fluxes are given at cell centers: average over eight innermost grid cells
Compute time-integrated flux (so-called „fluence“):
F =
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⇢|u|Z
Amp
t
From this, calculate surface density of atoms deposited on Earth at time t
before present (assuming isotropic fall-out); uptake factor only poorly known;
we use U = 0.6% (Knie et al. 2004)
⌃(t) =
U
F exp( t/⌧1/2 )
4
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Obtain number density of 60Fe for each crust layer by summing Σ(t) within the
corresponding time intervals and dividing it through the thickness of the layer
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Finally, relate this density to the one of stable iron (i.e. 60Fe/Fe) using
Michael Schulreich
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
Chemical mixing simulations with homogeneous background medium
(n = 0.1 cm-3, T = 104K)
Movies of SB evolution (Δx = 0.7 pc; cuts through z = 0 and y = 0)
Michael Schulreich
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
Chemical mixing simulations with homogeneous background medium
Maps of the 60Fe density distribution with SN explosion centers (cuts through y = 0 and z = 0)
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No structures that can restrict (or promote)
superbubble growth in certain directions
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LB extent in the Galactic disk exceeds
observationally derived values
no sufficient elongation in z-direction
Overall size and shape of the LB not very important for
modelling 60Fe amount that arrives on Earth
Michael Schulreich
The Local Bubble
But, gas-dynamical properties of region between SN
explosion centers and locus of the Earth is crucial
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determines arrival time of the LB‘s outer shell
sets the date for the earliest possible 60Fe signal in
terrestrial archives
Increased density by order of magnitude (n = 1 cm-3)
➔ Solar system is not reached in the time required
Superbubbles, HI holes and Supershells - 10/11/2014
Chemical mixing simulations with homogeneous background medium
Entropy maps, 60Fe fluence, and modeled 60Fe/Fe content in deep sea crust
Schulreich & Breitschwerdt (in prep.)
Michael Schulreich
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
Chemical mixing simulations with homogeneous background medium
Entropy maps, 60Fe fluence, and modelled 60Fe/Fe content in deep sea crust
Schulreich & Breitschwerdt (in prep.)
Michael Schulreich
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014
Conclusions
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The Local Bubble, a low-density X-ray emitting cavity deficient of HI, is our Galactic habitat
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Without it, we would perceive significantly fewer stars on the night sky and hence our knowledge of the cosmos
would certainly be less developed.
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Decipher its origin and present properties by remodelling its past
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Identify the SN precursors / most probable stellar trajectories
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Follow the superbubble‘s evolution by means of high-resolution numerical simulations that take into account the
turbulent multiphase nature of its environment ➔ reproduce observational features such as size, age, dynamical
instabilities in the interaction shell, etc.
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We can reproduce the 60Fe anomaly in deep ocean crusts by means of idealized analytical calculations and more
realistic chemical mixing simulations using passive scalars
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We are committed to a „bottom up“ approach: Add additional physical processes on a step by step basis in order to
gain knowledge of their influence and importance (e.g. non-equilibrium ionization ➔ Talk by Dieter Breitschwerdt)
Michael Schulreich
The Local Bubble
Superbubbles, HI holes and Supershells - 10/11/2014