Yes, Stars DO form by Gravitational Collapse Neal J. Evans II The University of Texas at Austin.
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Transcript of Yes, Stars DO form by Gravitational Collapse Neal J. Evans II The University of Texas at Austin.
![Page 1: Yes, Stars DO form by Gravitational Collapse Neal J. Evans II The University of Texas at Austin.](https://reader036.fdocuments.us/reader036/viewer/2022081521/5a4d1acb7f8b9ab05996f8a3/html5/thumbnails/1.jpg)
Yes, Stars DO form by Gravitational Collapse
Neal J. Evans IIThe University of Texas at Austin
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A Brief History of Collapse
1968-9 Al Cheung, Townes, … discover ammonia, water
~1970 Molecular Clouds studied Lines much broader than thermal
1974 Goldreich and Kwan Linewidths caused by collapse
1974 Zuckerman and Evans Linewidths caused by turbulence
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A Brief History of Collapse
1980s Myers et al. etc Dense cores within clouds
1977 Shu Collapse of a singular isothermal sphere Inside-out collapse
1982 Wynn-Williams “Protostars are the Holy Grail of infrared
astronomy.” Collapsing protostar: the “holy grail”
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A Brief History of B335
Barnard (1905) Small round cloud, totally isolated
“[...] a very small black spot, B335, which looks like a defect, but is not. It is probably of the same nature as the larger ones just mentioned. It can hardly be a hole through the star cloud.’’ - E. E. Barnard, from his comments on Plate 41, August 27, 1905
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B335: The Theorists’ Dream
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More Recent Developments
B335 moved closer (100 pc instead of 250) Stutz 2008, Oloffson 2009
Spitzer, Herschel detected source at much shorter IR wavelengths Now have a full SED
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Detected now from 3.6 to 1300 micron.Spectrophotometry over much of that range.
Closer distance plus better photometry:L = 0.72 Lsun
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Observing Infall with ALMA
A key observation is to observe the infalling gas in redshifted absorption against the background protostar
Very high spectral resolution (<0.1 km/s) is required
High sensitivity to observe in absorption against disk.
(Slide from talks in mid 2000s about what we could do with ALMA)
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ALMA Exists!
66 Antennas at 5000 m altitude in the Atacama of Chile
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ALMA Observations
Re-assembled folks who worked on infall in late 90s
Proposed for Cycle 1 Eventually observed Continuum and four lines
CS 7-6, HCO+ 4-3, HCN 4-3, H13CN 4-3 Resolution ~ 0.5” and 0.1 km/s
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Continuum at 860 microns
Fit by 2D GaussianSize 0.53” by 0.47”(0.5” = 50 AU)Could be disk or inner part of envelope.Mass ~ 10–3 Msun
Also see arc structure; probably edge of outflow cavity
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Channel Maps of HCN
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Channel Maps of HCN
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Channel Maps of HCN
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Channel Maps of HCN
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Channel Maps of HCN
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Channel Maps of HCN
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Channel Maps of HCN
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Channel Maps of HCN
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Channel Maps of HCN
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The four lines towardcontinuum peak.Continuum has been subtracted, so TR < 0 means absorbing continuum.Blue line marks systemic velocity.We do see redshifted absorption in two lines.
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Updating the Model
Move closer (100 pc) rinf = 0.012 pc (~2500 AU) Age is 5 x 104 yr rin = 3 x 10–5 pc (= 6 AU)
Still spherical, still Shu model Add continuum source as observed Try simple abundance models for now
Step functions or “drop” functions
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Model in red For two lines with absorption against the continuum.Can reproduce the red-shifted dips reasonably well. Also the line wings from very inner part of infall; no need for outflow contribution.
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Summary
Clouds don’t collapse, cores do Unless the cloud IS a core (e.g., B335)
Evidence for collapse of cores has accumulated ALMA can provide “smoking gun” evidence B335 provides cleanest test
Data are qualitatively supportive of infall But puzzles remain