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Some Stars are Totally Metal: A New Mechanism Driving Dust Across Star-Forming Clouds, and Consequences for Planets, Stars, and Galaxies

Hopkins, Philip F. (2014) Some Stars are Totally Metal: A New Mechanism Driving Dust Across Star-Forming Clouds, and Consequences for Planets, Stars, and Galaxies. Astrophysical Journal, 797 (1). Art. No. 59. ISSN 0004-637X.

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Dust grains in neutral gas behave as aerodynamic particles, so they can develop large local density fluctuations entirely independent of gas density fluctuations. Specifically, gas turbulence can drive order-of-magnitude “resonant” fluctuations in the dust density on scales where the gas stopping/drag timescale is comparable to the turbulent eddy turnover time. Here we show that for large grains (size ≳ 0.1 µm, containing most grain mass) in sufficiently large molecular clouds (radii ≳ 1 - 10pc, masses ≳ 10^4M_⊙), this scale becomes longer than the characteristic sizes of pre-stellar cores (the sonic length), so large fluctuations in the dust-to-gas ratio are imprinted on cores. As a result, star clusters and protostellar disks formed in large clouds should exhibit substantial abundance spreads in the elements preferentially found in large grains (C, O). This naturally predicts populations of carbon-enhanced stars, certain highly unusual stellar populations observed in nearby open clusters, and may explain the “UV upturn” in early-type galaxies. It will also dramatically change planet formation in the resulting protostellar disks, by preferentially “seeding” disks with an enhancement in large carbonaceous or silicate grains. The relevant threshold for this behavior scales simply with cloud densities and temperatures, making straightforward predictions for clusters in starbursts and high-redshift galaxies. Because of the selective sorting by size, this process is not visible in extinction mapping. We also predict the shape of the abundance distribution – when these fluctuations occur, a small fraction of the cores are actually seeded with abundances Z ~ 100〈Z〉 such that they are almost “totally metal” (Z ~ 1)! Assuming the cores collapse, these totally metal stars would be rare (1 in ~ 10^4 in clusters where this occurs), but represent a fundamentally new stellar evolution channel.

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URLURL TypeDescription Paper
Hopkins, Philip F.0000-0003-3729-1684
Additional Information:© 2014 American Astronomical Society. Received 2014 July 4; accepted 2014 October 21; published 2014 November 25. Submitted to MNRAS, January, 2014. We thank Charlie Conroy, Selma de Mink, and Jessie Christiansen for many helpful discussions and sanity checks during the development of this work. We also thank Todd Thompson, Chris Matzner, Eric Pellegrini, Norm Murray, and Nick Scoville for some detailed discussions of the physical consequences for star formation and suggestions for observational comparisons and tests. We thank Matt Kunz, Avishai Gal-Yam, and Steve Longmore for helpful comments, including several ideas for follow-up work, and Peter Goldreich for stimulating discussions on the general physics involved. We thank Alvio Renzini for highlighting some unclear statements that may have been potential points of confusion. Support for P.F.H. and D.G. was provided by the Gordon and Betty Moore Foundation through Grant #776 to the Caltech Moore Center for Theoretical Cosmology and Physics, an Alfred P. Sloan Research Fellowship, NASA ATP Grant NNX14AH35G, and NSF Collaborative Research Grant #1411920. Numerical calculations were run on the Caltech compute cluster “Zwicky” (NSF MRI award #PHY-0960291) and allocation TG-AST130039 granted by the Extreme Science and Engineering Discovery Environment (XSEDE) supported by the NSF.
Group:TAPIR, Moore Center for Theoretical Cosmology and Physics
Funding AgencyGrant Number
Gordon and Betty Moore Foundation776
Alfred P. Sloan FoundationUNSPECIFIED
Subject Keywords:galaxies: evolution; galaxies: formation; hydrodynamics; protoplanetary disks; stars: formation
Issue or Number:1
Record Number:CaltechAUTHORS:20140707-083959908
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Official Citation:Some Stars are Totally Metal: A New Mechanism Driving Dust across Star-forming Clouds, and Consequences for Planets, Stars, and Galaxies Philip F. Hopkins 2014 ApJ 797 59
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:46867
Deposited By: Tony Diaz
Deposited On:07 Jul 2014 16:24
Last Modified:03 Oct 2019 06:47

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