Transcript presentation source

Erosion, Landfill & Politics in
Interstellar Space
Alyssa A. Goodman
Harvard University
Department of Astronomy
cfa-www.harvard.edu/~agoodman
Erosion,
Landfill
& Politics
At 9 P.M., I hope you have some idea of:
What we understand about
how stars like the Sun form,
and how we came to this
understanding
What we understand
"Cores" and
Outflows
1 pc = 3 lyr
Molecular or
Dark Clouds
Jets and
Disks
Solar System
Formation
What we also
understand, but
don’t always admit
Landfill
Magnetohydrodynamic
Waves
Infall
Outflows
MHD
Turbulence
H II Regions
Erosion
Thermal
Motions
SNe/GRB
Even though
it’s now
right
before
our eyes
How we came to our “modern” understanding
The Politics of Ideas
From admitting stars form, to modern complexity
Politics and Funding
Are the politicians and the public interested?
Ideas 1900-2000
Ideas: 1900-1948
Dust, not Holes
c. 1900: Barnard decides “dark” clouds are obscuring
material, not “holes” in the distribution of stars
ABCDEFG…  OBAFGKM...
c. 1920s-30s: work of Annie Jump Cannon, Henry
Norris Russell, and legions of others lead to decoding
stellar structure and evolution from spectra of stars
Protostars?
1947 Bok & Reilly suggest smallest Barnard objects
(now called “Bok Globules”) may be protostars
Dust,
Not Holes
Time Showed Barnard was Right!
Barnard’s Optical
Photograph of Ophiuchus
IRAS Satellite Observation,
1983
Remember: Cold (10K) dust glows, like a blackbody, in the far-infrared.
Ideas: 1900-1948
Dust, not Holes
c. 1900: Barnard decides “dark” clouds are obscuring
material, not “holes” in the distribution of stars
ABCDEFG…  OBAFGKM...
c. 1920s-30s: work of Annie Jump Cannon, Henry
Norris Russell, and legions of others lead to decoding
stellar structure and evolution from spectra of stars
Protostars?
1947 Bok & Reilly suggest smallest Barnard objects
(now called “Bok Globules”) may be protostars
Stellar Evolution from Spectroscopy:
The Hertzprung-Russell Diagram
Post ~1950 HR Diagram
Implies
•finite lifetime for stars
•need to replenish
stellar stock (“Star
Formation”!)
•need to form wide
variety of stellar types
A B C D E F G...
Ideas: 1900-1948
Dust, not Holes
c. 1900: Barnard decides “dark” clouds are obscuring
material, not “holes” in the distribution of stars
ABCDEFG…  OBAFGKM...
c. 1920s-30s: work of Annie Jump Cannon, Henry
Norris Russell, and legions of others lead to decoding
stellar structure and evolution from spectra of stars
Protostars?
1947 Bok & Reilly suggest smallest Barnard objects
(now called “Bok Globules”) may be protostars
“The Possibility of Star Formation”
Bok’s Globules
1948-49
“[Owing to nuclear physicists good proposal of a ‘big
bang’ origin of the Universe some 3 million years ago…]
We are indeed forced to conclude that the present
variety of stars in the sky is the result of the original
method of star formation rather than of any
evolutionary process.”
--Lyman Sptitzer, 1948
“[Even though T Tauri associations could all have similar
colors implying young age by coincidence], it is of
course, tempting to search for a connection between
the T Tauri stars and Bok’s ‘globules,’ but we must
admit that at present there is no evidence of any
objects intermediate between the two groups.”
--Otto Struve 1949
What Happened around 1950?
HR Diagram comes into focus
• Globular cluster stars clearly very old (>few Gyr)
• T Tauri and other “pre-main-sequence”stars clearly
very young (few Myr)
• Real admitted need for star formation
Radio Astronomy finds the Neutral ISM
1951 Ewen & Purcell detect 21-cm emission from
interstellar hydrogen out the window of Harvard’s
Jefferson Labs (appreciated as massive amounts of gas, but not
concentrated on Bok Globules…)
$ NSF Founded $ (1950) (Keep in mind...NASA Founded 1958)
Suddenly, by 1952 “Star Formation”
was a Respectable Term & Subject!
“The suggestion that all type I stars have been formed
from the interstellar clouds may, perhaps, be taken as
a working hypothesis.”
--Schwarzschild, Spitzer & Wildt 1951
“This, I imagine, is why the oldest members of the stellar
system…are so large and populous, for the available
material was richer then. As the layer of dust and gas
sank toward the galactic plane, stars continued to
form. Dust and gas still lie dense in this layer, and stars
are still being formed there.
--Cecilia Payne Gaposchkin 1952
Tutorial:
Velocity from
Spectroscopy
Observed Spectrum
Telescope 
Spectrometer
1.5
Intensity
1.0
0.5
0.0
All thanks to Doppler
-0.5
100
150
200
250
"Velocity"
300
350
400
Tutorial:
Velocity from
Spectroscopy
Observed Spectrum
Telescope 
Spectrometer
1.5
Intensity
1.0
0.5
0.0
All thanks to Doppler
-0.5
100
150
200
250
"Velocity"
300
350
400
Bok’s Dream: Radio Spectral-line Observations of Interstellar Clouds
Spectral Line Observations
Bok’s Dream: Radio Spectral-line Observations of Interstellar Clouds
Radio Spectral-Line Survey
Alves, Lada & Lada 199
And someone had to pay for
it...
The 26-m Telescope at
Agassiz Station
Harvard, MA
Cost in 1956: $200,000
1957 H I
Spectroscopy
Telescope 
Spectrometer
All thanks to Doppler
H I Spectrum of the Galaxy M51
from Agassiz Station,Heeschen 1957
Ideas: 1952-1975
Making Stars from Gas Clouds
1953 Hoyle’s proposal of hierarchical fragmentation by
Jeans instability (Jeans masssmallest mass that will collapse under
self-gravity in homogeneous medium of given density & temperature)
1963 Layzer points out smallest clumps might collide &
stick
Protostars?
c. 1952 Herbig & Haro find non-stellar bright knots
associated with “dark clouds” (HH Objects)
Molecules in Space, Molecular Clouds
CH absorption (1940); OH absorption (1963) emission (1965); CO
emission (1970)
Emission associated with & dark clouds Bok Globules
Star Formation c. 1953
Fragments Collapse Under
Gravity into “Protostars”
time~105 years
Global Instability (e.g. Jeans)
Fragments Cloud (hierarchically)
time~106 years
Hoyle 1953
Star Formation in 1953
A Group of Young
“Zero-Age Main Sequence”
Stars is Born
HH Objects
“Giant”
Herbig-Haro
Flows:
PV Ceph
1 pc
Reipurth, Bally & Devine 1997
Velocity as a "Fourth" Dimension
Spectral Line Observations
Loss of
1 dimension
Mountain Range
No loss of
information
“Integrated Intensity Map”
Region of Radio Spectral-Line Survey
Alves, Lada & Lada 199
Ideas: 1975-1985
More Collapse and Fragmentation Scenarios
1970s-now Resurgence of “Triggered” Star Formation
Ideas (Erosion, Landfill)
Triggers: SNe, H II Regions, cloud-cloud collisions,
shocks, star formation itself
Protostars?
1970s-now Infrared detectors unveil the youngest stars
1975 KAO begins flights; 1983 IRAS Satellite
Oops! Bipolar Outflows
(More erosion & landfill?)
1980 Unpredicted discovery of bipolar flows
associated with HH objects
The Story, c. 1990
"Cores" and
Outflows
1 pc = 3 lyr
Molecular or
Dark Clouds
Jets and
Disks
Solar System
Formation
Molecular Clouds "Created" by Supernovae
100 mm Dust Emission in Cassiopeia
Tóth et al. 1995
Star Formation Triggered by A Galaxy Collision
HST Image of the Antennae, Whitmore et al.
The Star-Forming
Interstellar Medium
Magnetohydrodynamic
Waves
Infall
Outflows
MHD
Turbulence
SNe/GRB
H II Regions
Thermal
Motions
Ideas: 1985-now
Magnetic Fields
1937 Alfvén proposes Galactic B; 1949-1951 appreciation of
polarization by magnetically-aligned dust; 1968 1st Zeeman
observations; 1988 The bandwagon drives off...
Protostellar Disks
1980s,90s Interferometer Disks; 1990s HST Disks
*Clumping, Turbulence, Clustering and the IMF
c. 1990- Big Maps, “Big Pictures”
*Environmental Influences
c. 1990s HST reminds us about Erosion & Landfill
Do Magnetic Fields Explain Everything?
(line width)~(size)1/2
(density)~(size)-1
Curves assume M=K=G
(Myers & Goodman 1988)
Erosion
My Ideas
The Spectral Correlation Function
Figure from Falgarone et al. 1994 Simulation
Strong vs. Weak B-Field
b=0.01
Stone, Gammie & Ostriker 1999
[T / 10 K]
b[
2
-3
nH / 100 cm ][ B / 1.4 mG]
2
b=1
•Driven Turbulence; M K; no gravity
•Colors: log density
•Computational volume: 2563
•Dark blue lines: B-field
•Red : isosurface of passive contaminant after saturation
The Superstore
Learning More from “Too Much” Data
1950
10
pixels
10
10
10
10
1980
1990
2000
8
Product
10
7
4
6
10
5
3
N channels
4
S/N
10
N pixels
10
3
2
1
2
10
1950
1960
1970
1980
Year
1990
2000
0
Npixels
(S/N)*N
10
1970
Nchannels, S/N in 1 hour,
*N channels
10
1960
How the SCF Works
Measures similarity
of neighboring
spectra within a
specified “beam”
size
lag & scaling
adjustable
signal-to-noise
accounted for
See: Rosolowsky, Goodman,
Wilner & Williams 1999; Padoan,
Rosolowsky & Goodman 1999.
Which one of these is not like the
others? Increasing Similarity of Spectra to Neighbors
0.8
Rosette C 18O
0.6
SNR
13CO
Rosette
13CO
L134A 13CO(1-0)
Rosette C 18O Peaks
Pol.
13CO(1-0)
L1512 12CO(2-1)
G,O,S
0.2
Peaks
HCl2 C 18O
H I Survey
0.4
Rosette
L134A 12CO(2-1).
HCl2 C 18O Peaks
MacLow et al.
HLC
Increasing Similarity of ALL Spectra in Map
Change in Mean SCF with Randomization
1.0
Falgarone et al.
0.0
0.0
0.2
0.4
0.6
Mean SCF Value
0.8
1.0
1.2
“Giant”
Herbig-Haro
Flows:
PV Ceph
1 pc
Reipurth, Bally & Devine 1997
A New
Proposal:
Episodic
ejections
from
precessing or
wobbling
moving
source
Required motion of 0.25 pc
(e.g. 2 km s-1 for 125,000 yr)
67:55
HH 31 5C
HH 31 5B
PV Ceph
67:50
HH 315 A
H H 415
HH
215P2
HH
215P1
PV Cephei
67:45
12CO
(2-1) OTF
Map from NRAO 12-m
HH 315D
HH 31 5E
Red: 3.0 to 6.9 km s-1
Blue: -3.5 to 0.4 km s-1
Arce & Goodman 2000
67:40
HH 31 5F
20:46
20:45
a (1950)
How much of a molecular cloud complex was
“moved” to its present location by an outflow?
Movie of Taurus
Key:
Blue
34%
"Cloud" 56%
Red
10%
(by mass)
.
Astronomy Politics and Funding
What do we need to pay for?
New Observatories
e.g. 1 Keck or SMA  $75M; 1 HST  $3000M
People
~120 PhD’s produced/year, 50% go on to become
astronomers, each doing ~2 postdocs
Research Grants
To Individuals
To Private Research Facilities/Observatories
To “National Observatories”
Astronomy Politics and Funding
Where does the money come from today?
Generous Individuals
& Foundations (sponsoring
University-based efforts)
~$100s of millions/year
>$1 Billion/year
~$100s millions/year
~$100 million/year
Disclaimer: These are rough, order-of-magnitude estimates by the speaker.
NASA’s Origins Program