Order, Chaos and the Space Between the Stars Alyssa A. Goodman Harvard-Smithsonian Center for Astrophysics WIYN Image: T.A. Rector (NOAO/AURA/NSF) and Hubble Heritage Team (STScI/AURA/NASA)

Truth Truth in (my) Science How does the gas between the stars arrange and re-arrange itself in the process of forming new stars? Truth in Religion What does it mean to lead a “good” life?

History + Principles — Dogma = Truth

Dogma The word dogma (Gr. dogma from dokein) signifies, in the writings of the ancient classical authors, sometimes, an opinion or that which seems true to a person; sometimes, the philosophical doctrines or tenets, and especially the distinctive philosophical doctrines, of a particular school of philosophers (cf. Cic. Ac., ii, 9), and sometimes, a public decree or ordinance, as dogma poieisthai.

History + Principles — Dogma  Truth

History + Principles — Dogma  Truth …as applied to the formation of new stars, & the observation of magnetic fields in star-forming regions Tonight

Order

WIYN Image: T.A. Rector, B. Wolpa and G. Jacoby (NOAO/AURA/NSF) and Hubble Heritage Team (STScI/AURA/NASA) Chaos

Molecular or Dark Clouds "Cores" and Outflows “Order” Jets and Disks Extrasolar System 1 pc

Magnetic Dogma, c : Order

Outflows Magnetohydrodynamic Waves Thermal Motions MHD Turbulence Inward Motions SNe/GRB H II Regions Chaos B

The Truth: Order in a Sea of Chaos "Rolling Waves" by KanO Tsunenobu © The Idemitsu Museum of Arts.

The “Truth” about Interstellar Magnetic Fields History Cosmic rays, synchrotron emission, polarization, Zeeman effect Principles Maxwell’s Equations + Fluid Equations = “magnetohydrodynamics” [MHD], Gravity Dogma Flux-freezing, Aligned Grains, The Angular Momentum Problem, Outflow Confinement, and other Words of the Wise Truth A difficult-to-measure and “messy” field whose role varies depending upon conditions. “Ongoing cosmic creativity.” (G. Kaufman)

Pre-1980 History of B in the Galaxy 1949 discovery of polarization of background starlight (Hall, Hiltner) 1950 observational/theoretical understanding of cosmic ray confinement & strength of magnetic field in the Milky Way (Chandrasekhar, Fermi, Kiepenheuer, Spitzer) optical & radio recognition of “synchrotron” emission 1950 interpretation of polarization as due to magnetically- aligned dust in space (Davis & Greenstein) 1968 Zeeman effect (direct measure of field strength) detected for the 1st time--strength as “predicted” (Verschuur) 1970’s large-scale mapping of “background starlight” polarization

Pre-1980 History Relevant Tonight 1949 discovery of polarization of background starlight (Hall, Hiltner) 1968 Zeeman effect (direct measure of field strength) detected for the 1st time--strength as “predicted” (Verschuur) 1970’s large-scale mapping of “background starlight” polarization

Principles: Gravity & Electromagnetism 1873 Maxwell publishes his unifying theory of electrodynamics, which is expressed in just four equations 1943 Alfvén publishes “On the Existence of Electromagnetic-Hydrodynamic Waves” 1687 Newton publishes the Principia, setting out his theory of gravity

Principles: Fluids 1851 Stokes publishes “Navier-Stokes equations describing a “laminar” flow 1975 advent of “numerical simulations” of turbulent flow (Woodward publishes first hydrodynamic simulation of a molecular cloud (using bomb codes)) 1990’s 1st “magnetic” simulations carried out Woodward 1976

Outflows Magnetohydrodynamic Waves Thermal Motions MHD Turbulence Inward Motions SNe/GRB H II Regions What is the true role/shape of the magnetic field here?

One more bit of History (which later, unfortunately, became Dogma) AG’s Ph.D. thesis (1989) work showed… –Historical B-field measurements were, in Principle, consistent with a picture where B is strong enough to matter in cloud dynamics –New B-field measurement (just one!) confirmed this hypothesis  “Dogmatic” view of “energetically significant” magnetic fields

Outflows Magnetohydrodynamic Waves Thermal Motions MHD Turbulence Inward Motions SNe/GRB H II Regions What is the true role/shape of the magnetic field here?

The History of a Star/Disk/Outflow System figure based on Kaifu et al. 1984

Mapping Magnetic Fields: “Background Starlight Polarimetry”

Rorschach Test

Dogma, c. 1985

Principle or Dogma? Dark CloudAmbient ISM Cloud Envelope 1 A =5>1051mag Cloud Envelope Background Star Observer Dark Cloud is a Local Denisty Maximum along l.o.s. --so the polarization observed gives B- field THERE "Dark Cloud" Density Distance along Line of Sight

Recall the Dogma Uchida & Shibata 1985

Does this violate Dogma, Steve? figure based on Kaifu et al. 1984

Dark Cloud Complexes: 1-10 pc scales

B

Cold Dark Clouds: Looking Inside(?) Goodman et al. 1992

What if… Not all Grains are Created Equal? Less Dust, Much Polarization Much Dust, no Polarization Less Dust, Much Polarization Goodman et al. 1995

Dark CloudAmbient ISM Cloud Envelope 1 A = V 5>1051mag Changes in the Efficiency of Polarization Along a Line of Sight Density Distance Along Line-of-Sight Polarization Efficiency Polarization Efficiency Drops w/in "Dark Cloud" is a Local Density Maximum Along l.o.s. Cloud Envelope Background Star Observer "Dark Cloud"

Result: “Pioneering a Dead End” A V [magnitudes] Polariztion [%] ? Polarization May Show NO Increase with Extinction! "Dark Cloud" Affects the Extinction, but NOT the Polarization

Polarization [%] Cold Dark Clouds: (Not) Looking Inside Extinction [mag] B (Goodman et al. 1992) L1755 (Goodman et al. 1995) Galaxy (Jones, Klebe & Dickey 1992) Fit to these dark clouds More Stuff Amount of Polarization

New History: Background Starlight Polarimetry cannot probe B-field “inside” Dark Clouds Not Sensitive to B-Field Here What does that mean?

Dark Cloud Complexes: 1-10 pc scales

“Go no further than A V ~1.3 mag.” P R [%] A V [mag] Background to Cold Dark Cloud Arce et al Background to General ISM

A Better Path to Truth? Look at the Grains’ Own Emission

©National Geographic The “Canonical” Example: Orion

Clinging to Dogma? Schleuning et al HST/NICMOS

What is the field doing? Figure from: Kannappan & Goodman 1998

What is the field doing? Figure from: Kannappan & Goodman 1998 HII Region

Does Any Polarimetry tell “The Truth”? Does polarization map give true field structure? Polarization drops as density increases (similar to background starlight story) Plots and data from Henning, Wolf, Launhart & Waters 2001

Simulated Truth 3D MHD simulation of Gammie, Stone & Ostriker Field lines “look” straight-ish, even though B is significant.

Simulated Truth Padoan, Goodman, Draine, Juvela,Nordlund, Rögnvaldsson D simulation super-sonic super-Alfvénic self-gravitating Model A: Uniform grain- alignment efficiency

Simulated Truth Padoan, Goodman, Draine, Juvela,Nordlund, Rögnvaldsson D simulation super-sonic super-Alfvénic self-gravitating Model B: Poor Alignment at A V ≥3 mag

Dense Cores Padoan, Goodman, Draine, Juvela,Nordlund, Rögnvaldsson 2001

Polarization vs. How Much Stuff Padoan, Goodman, Draine, Juvela,Nordlund, Rögnvaldsson 2001

Observations + Theory — unfounded generalization = Truth History + Principles — Dogma = Truth

Dynamic Creativity work in progress by Bate, Bonnell & Bromm