1. Yes, Stars DO form by Gravitational Collapse Neal J. Evans II The University of Texas at Austin

2. 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

3. 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”

4. 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

5. B335: The Theorists’ Dream

6. 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

7. Detected now from 3.6 to 1300 micron. Spectrophotometry over much of that range. Closer distance plus better photometry: L = 0.72 L sun

8. 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)

9. ALMA Exists! 66 Antennas at 5000 m altitude in the Atacama of Chile

10. 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, H 13 CN 4-3  Resolution ~ 0.5” and 0.1 km/s

11. Continuum at 860 microns Fit by 2D Gaussian Size 0.53” by 0.47” (0.5” = 50 AU) Could be disk or inner part of envelope. Mass ~ 10 –3 M sun Also see arc structure; probably edge of outflow cavity

12. Channel Maps of HCN

21. The four lines toward continuum peak. Continuum has been subtracted, so T R < 0 means absorbing continuum. Blue line marks systemic velocity. We do see redshifted absorption in two lines.

22. Updating the Model  Move closer (100 pc)  r inf = 0.012 pc (~2500 AU)  Age is 5 x 10 4 yr  r in = 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

23. 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.

24. 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