The Formation of Molecular Clouds and Massive Stars

Prof. Mordecai-Mark Mac Low


In this talk I consider two questions. First, I investigate the formation of molecular clouds from diffuse interstellar gas. It has been argued that the midplane pressure controls the fraction of molecular hydrogen present, and thus the star formation rate. Alternatively, I and others have suggested that the gravitational instability of the disk controls both. I present numerical results demonstrating that the observed correlations between midplane pressure, molecular hydrogen fraction, and star formation rate can be explained within the gravitational instability picture. Second, I discuss how ionization affects the formation of massive stars. Although most distinctive observables of massive stars can be traced back to their ionizing radiation, it does not appear to have a strong effect on their actual formation. Rather, I present simulations suggesting that stars only ionize large volumes after their accretion has already been throttled by gravitational fragmentation in the accretion flow. At the same time these models can explain many aspects of the observations of ultracompact H II regions.

About the talk

The Formation of Molecular Clouds and Massive Stars
Prof. Mordecai-Mark Mac Low
Department of Astrophysics, American Museum of Natural History, New York, USA
Thursday July 7, 2011 - 0:00 GMT+1  (Aula)
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About the speaker

Dr. Mac Low's work focuses on understanding the formation of planets, stars, and galaxies. Working with students and colleagues, he has developed numerical models at different physical scales to attack these problems. At the smallest scales, he is studying the interaction of planets with their natal circumstellar disks.  At scales of less than one light year, he has simulated the behavior of self-gravitating, supersonic, magnetized turbulence to understand the formation of the dense cloud cores in which protostars are observed, and has modeled the expansion of ionized regions in such turbulence.  At scales of hundreds to thousands of light years, he is studying the influence of multiple supernova explosions on the interstellar gas, and how clouds of star-forming molecular gas form.  Finally, at the galactic scale of tens of thousands of light years, he studies the large-scale formation of stars in galaxies.

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