December 2009

Ralph Pudritz
Department of Physics & Astronomy
McMaster University

Dear Prospective Graduate Student,

My research focuses on the theoretical and numerical study of star and planet formation, and recently on how biomolecules such as amino acids form in astrophysical environments. Star formation plays a central role in astrophysics because it impacts a wide range of processes - from planet formation in protostellar disks, to galaxy formation and evolution, and even cosmology. The discovery of more than 200 extrasolar planets, some with as little as five Earth masses, has revolutionized our thinking about how planetary systems form and evolve. The advent of new observatories such as the James Webb Space Telescope, as well as the Atacama Large Millimeter Array (ALMA) will allow us to study these processes with unprecedented resolution. There could not be a better time to be working on these fundamental questions.

My research in star formation explores a wide range of interconnected problems. My ultimate goal is to develop a seamless picture of star formation, starting from the scale of the galaxy, down to the scales at which molecular clouds are formed, to the formation of star clusters within these clouds, to the collapse of individual gas “cores” within such clustered environments (to form single or binary stars), and on down to the scales that characterize the physics of protostellar disks through which gas accretes onto their central stars and from which highly collimated jets are launched. Together with my students, postdocs, and collaborators, we have pioneered the study of jets from protostellar disks that are observed around all young stars. We have also shown that outflows arise as an intrinsic part of gravitational collapse of molecular cloud cores. On larger scales, we have simulated the earliest stages of the formation of star clusters within the densest clumps of dusty, magnetized gas within molecular clouds. Students in my group use state of the art, Adaptive Mesh Refinement codes to follow this process from parsec to stellar spatial scales. This research is also the first step towards understanding how star clusters and the well known mass distribution of stars (the so-called “initial mass function”) arise. An important application of this work on cluster formation is towards an understanding of how the earliest stars and globular clusters formed at high red shifts. My group has also gone deeply into the astrophysics of the disks out of which stars and planets arise.

Our planetary studies have investigated how planetary systems form and migrate within their natal disks. It is believed that the “hot Jupiters” that are found in extrasolar systems were not formed close to their central star, but rather migrated from larger distances out in their disks. My students and I have worked on new theories and models for how planets migrate in gas disks, and on what might prevent them from “splashing” into their central stars. Currently, I am interested in extending this research to the question of how terrestrial planets form and am currently just starting new work with students on this question.

Through my involvement in the Origins Institute, I have now started to work (together with some graduate students) on trying to understand the origin and evolution of biomolecules. The presence of amino acids within meteorites shows that such biomolecules were probably made within protostellar disks, and survived their delivery to the Earth. We are examining the astrochemistry of such molecule formation, with the intent of understanding how pre-biotic conditions arose on terrestrial planets. This is a significant step towards understanding the origins of life on Earth, and possibly in other planetary systems.

I currently have four graduate students and a postdoc working in my group. My students work on both theoretical and numerical aspects of these problems. I try to ensure that my students work on linked problems. Through group meetings, we stay in close contact with one another so that students don’t work in isolation but are all part of a larger picture. Research is open-ended, and I believe in having students work on problems that are at the cutting edge in any given field. The exact problem that a student works on is a mix of their interests and mine. By the end of their work in my group, my students are working as independent researchers and are leaders in their field. My students have done very well in their careers - with three of my six completed Ph.D. students working as faculty members in universities, two currently working as postdocs, and one working in a research position in climate modeling. I have had a number of outstanding postdoctoral research fellows working in my group, and this has been excellent for my students as well.

I have many interesting research projects within this broad set of themes. I will be happy to discuss these with you. If you are interested, please send me e-mail at or consult my departmental home page. I look forward to hearing from you!

With best wishes,
Ralph Pudritz