Yes, Stars DO form by Gravitational Collapse

Neal J. Evans IIThe University of Texas at Austin

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

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”

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

B335: The Theorists’ Dream

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

Detected now from 3.6 to 1300 micron.Spectrophotometry over much of that range.

Closer distance plus better photometry:L = 0.72 Lsun

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)

ALMA Exists!

66 Antennas at 5000 m altitude in the Atacama of Chile

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

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

Channel Maps of HCN

Channel Maps of HCN

Channel Maps of HCN

Channel Maps of HCN

Channel Maps of HCN

Channel Maps of HCN

Channel Maps of HCN

Channel Maps of HCN

Channel Maps of HCN

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.

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

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.

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