A Dynamic View of Star Formation
Alyssa A. Goodman
cfa-www.harvard.edu/~agoodman
Harvard-Smithsonian Center for Astrophysics
WIYN Image: T.A. Rector, B. Wolpa and G. Jacoby (NOAO/AURA/NSF) and Hubble Heritage Team (STScI/AURA/NASA)
Time: The lost concept of elementary Physics
Glossary
Molecular Cloud: concentration of molecular (H2 rather than Outflow: molecular gas observed as “redshifted” and
the sky
atomic H) gas that often collapses to form stars
Spectral-line Map: spectra observed at a grid of pixels on Extinction: the blocking out of light by shmootz (dust) “Thermal” Emission: blackbody radiation (eg. from dust)
“blueshifted” emission on either side of a young, forming star
How are Molecular Clouds Observed?
The Oschin telescope, 48-inch aperture wide-field Schmidt camera at Palomar
Red Plate, Digitized Palomar Observatory Sky Survey
Extinction & “Thermal” Emission
Barnard’s Optical Photograph of Ophiuchus
IRAS Satellite Observation, 1983
Cold (10K) dust glows, like a blackbody, in the far-infrared.
Velocity from Spectroscopy
Observed Spectrum
Telescope Spectrometer
Intensity
1.5
1.0
0.5
0.0
All thanks to Doppler
-0.5 100 150 200 250 300 350 400
"Velocity"
Velocity from Spectroscopy
Observed Spectrum
Telescope Spectrometer
Intensity
1.5
1.0
0.5
0.0
All thanks to Doppler
-0.5 100 150 200 250 300 350 400
"Velocity"
Radio Spectral-line Mapping
Spectral Line Observations
Radio Spectral-line Mapping
Radio Spectral-Line Survey
Alves, Lada & Lada 1999
Velocity as a "Fourth" Dimension
Spectral Line Observations
Loss of 1 dimension No loss of information
Mountain Range
Question for this afternoon: Is there ever an “equilibrium” starting condition for forming stars?
Standing Still, Until the Last Minute
Fragments Collapse Under Gravity into “Protostars” time~105 years
Global Instability (e.g. Jeans) Fragments Cloud (hierarchically) time~106 years
Hoyle 1953
Standing Still, Until the Last Minute
A Group of Young “Zero-Age Main Sequence” Stars is Born
(One Round of) Star Formation, from “t=0”
"Cores" and Outflows
1 pc
Molecular or Dark Clouds
Jets and Disks Extrasolar System
BUT…
• How long does each “phase” last and how are they mixed?
•
•
What is the time-history of star production in a “cloud”? Are all the stars formed still “there”?
How do processes in each phase impact upon each other? (Sequential star formation, outflows reshaping clouds…)
Can we simulate ticking time?
Magnetohydrodynamic Computer Simulations give good approximation* of dynamic ISM, on >>0.1 pc scales
(*they still need much help)
What is the right “starting” condition?
b=0.01
b=1
Stone, Gammie & Ostriker 1999
[T / 10 K ] b=[ 2 -3 nH / 100 cm ][ B / 1.4 mG]
2
•Driven Turbulence; M K; no gravity •Colors: log density •Computational volume: 2563 •Dark blue lines: B-field •Red : isosurface of passive contaminant after saturation
Evaluating Simulated Spectral Line Map of MHD Simulations: The Spectral Correlation Function (SCF)
Simulated map, based on work of Padoan, Nordlund, Juvela, et al. Excerpt from realization used in Padoan, Goodman & Juvela 2002.
How Well can Molecular Clouds be Modeled, Today? Summary Results from SCF Analysis
Falloff of Correlation with Scale
“Equipartition” Models
“Reality”
“Stochastic” Models
Scaled “Superalfvenic” Models
Padoan, Goodman & Juvela 2002
Magnitude of Spectral Correlation at 1 pc
And can we go beyond 0.1 pc?
•MHD turbulence gives “t=0” conditions; Jeans mass=1 Msun •50 Msun, 0.38 pc, navg=3 x 105 ptcls/cc •forms ~50 objects •T=10 K •SPH, no B or L, G
•movie=1.4 free-fall times Bate, Bonnell & Bromm 2002
But: Cores can be “Islands of Calm in a Turbulent Sea”
"Rolling Waves" by KanO Tsunenobu © The Idemitsu Museum of Arts.
Islands of Calm in a Turbulent Sea
Goodman, Barranco, Wilner & Heyer 1998
Order in a Sea of Chaos
~0.1 pc
(in Taurus)
Order; N~R0.9
Chaos; N~R0.1
Why care so much about time?
10
0
Power-law Slope of Sum = -2.7
(arbitrarily >2) 10
-1
Slope of Each Outburst = -2
as in Matzner & McKee 2000
Mass [Msun]
10
-2
10
-3
10
-4
10
-5
2
3
4 5 6 78
2
3
4
5 6 78
2
0.1
1
10
Velocity [km s-1]
Example 1: Episodicity changes outflow’s Energy/Momentum Deposition/time
Example 2: (Some) Young stars may zoom through ISM
Outflows
See references in H. Arce’s Thesis 2001
Example 2: Powering source of (some) outflows may zoom through ISM
“Giant” HerbigHaro Flow from PV Ceph
Goodman & Arce 2002
“Giant” HerbigHaro Flow from PV Ceph
1 pc
Image from Reipurth, Bally & Devine 1997
PV Ceph
Episodic ejections from a precessing or wobbling moving ?? source
Goodman & Arce 2002
Just how fast is PV Ceph going?
4x10
18
Insights from a “Plasmon” Model
500x10
15
70
3
Star 400
Distance along x-direction (cm)
60
Knot Offset/Star Offset (Percent)
y knot positions (cm)
Star-Knot Difference (%) 300 Star-Knot Difference
50
2
40
30 200 20
1
Knot 100
0 -4x10
17
Initial jet 250 km s1; star motion 10 km s-1
-2 0
10
0 0 5 10 15x10 Elapsed Time since Burst (Years)
3
0
x knot posns. w.r.t. star "now" (cm)
Goodman & Arce 2002
How Many Outflows are There at Once?
What is their cumulative effect?
Action of Outflows(?) in NGC 1333 SCUBA 850 mm Image shows Ndust
(Sandell & Knee 2001)
Dotted lines show CO outflow orientations (Knee & Sandell 2000)
The COordinated Molecular Probe Line Extinction Thermal Emission Survey
?
Nagahama et al. 1998 13CO (1-0) Survey
Un(coordinated) MolecularProbe Line, Extinction and Thermal Emission Observations
Molecular Line Map
2MASS/NICER Extinction Map of Orion
1:50
50
1 pc
2:00
55
2:00
05
10
10
15
20
20
1 pc
30
25
SCUBA
30 40 5:41:00 20 40 R.A. (2000) 42:00
40
SCUBA
42:00 30 41:00 R.A. (2000) 30 5:40:00
Johnstone et al. 2001
Lombardi & Alves 2001
Johnstone et al. 2001
The Value of Coordination
Optical Image
Dust Emission
C18O
Coordinated Molecular-Probe Line, Extinction & Thermal Emission Observations of Barnard 68 This figure highlights the work of Senior Collaborator João Alves and his collaborators. The top left panel shows a deep VLT image (Alves, Lada & Lada 2001). The middle top panel shows the 850 mm continuum emission (Visser, Richer & Chandler 2001) from the dust causing the extinction seen optically. The top right panel highlights the extreme depletion seen at high extinctions in C18O emission (Lada et al. 2001). The inset on the bottom right panel shows the extinction map derived from applying the NICER method applied to NTT near-infrared observations of the most extinguished portion of B68. The graph in the bottom right panel shows the incredible radial-density profile derived from the NICER extinction map (Alves, Lada & Lada 2001). Notice that the fit to this profile shows the inner portion of B68 to be essentially a perfect critical Bonner-Ebert sphere
NICER Extinction Map
Radial Density Profile, with Critical Bonnor-Ebert Sphere Fit
The COordinated Molecular Probe Line Extinction Thermal Emission Survey
COMPLETE
sampling as a path to the answer
Alyssa A. Goodman, Principal Investigator (CfA) João Alves (ESA, Germany) Héctor Arce (Caltech) Paola Caselli (Arcetri, Italy) James DiFrancesco (HIA, Canada) Mark Heyer (FCRAO/UMASS) Doug Johnstone (HIA, Canada) Scott Schnee (CfA, PhD student) Mario Tafalla (OAS, Spain) Tom Wilson (MPIfR/SMTO)
The COordinated Molecular Probe Line Extinction Thermal Emission Survey
Molecular Probe Line Maps (give velocity, density & temperature structure) Extinction Maps(optical and near-IR star counts & colors give density structure) Thermal Emission Maps (give density and temperature structure)
?
Why hasn’t this been done before?
10
3
13CO
1 day for a map then
A V~5 mag, Resolution~1' A V~30 mag, Resolution~10" CO Spectra for 32 Positions in a Dark Cloud (S/N~3) Sub-mm Map of a Dense Core at 450 and 850 mm
13
10
2
1 Week 1 Day
10
Time (hours)
1
10
0
1 Hour NICER/8-m 1 Minute
10
-1
SEQUOIA+ 10
-2
1 minute for a 13CO map now
SCUBA-2
10
-3
1 Second 10
-4
NICER/2MASS 1985 1990 1995 2000 Year
NICER/SIRTF 2005 2010 2015
1980
SIRTF Legacy Survey
Perseus Molecular Cloud Complex (one of 5 similar regions to be fully mapped in far-IR by SIRTF Legacy)
SIRTF Legacy Survey
MIRAC Coverage
2 degrees ~ 10 pc
Pilot COMPLE TE Data
COMPLETE Preview: Discovery of a Heated Dust Ring in Ophiuchus
2 pc
Goodman, Li & Schnee 200
…and the famous “1RXS J162554.5-233037” is right in the Middle !?
2 pc
The answer is not (yet) in the back of the book.
Is there ever an “equilibrium” starting condition for forming stars?
A Dynamic View of Star Formation
Alyssa A. Goodman
cfa-www.harvard.edu/~agoodman
Harvard-Smithsonian Center for Astrophysics
WIYN Image: T.A. Rector, B. Wolpa and G. Jacoby (NOAO/AURA/NSF) and Hubble Heritage Team (STScI/AURA/NASA)