David F. Chernoff
Professor of Astronomy
Director of Graduate Studies
Ph.D. 1985 (U.C. Berkeley)
Campus Address:
602 Space Sciences Building
Cornell University
Ithaca, NY 14853
Email: chernoff at astro.cornell.edu
Phone: 607-255-4755
Specialty Areas: Theoretical Astrophysics
Research Projects: Calculations of Evolution of Star Clusters Including Degenerate Objects, Coalescence of Spinning, Binary Black Holes, Cosmological Mergers of Galaxies and Massive Black Holes, Opacity of H- at High Density
Biography: David F. Chernoff has worked on a variety of topics (evolution of star clusters, collisionless and collisional stellar dynamics, plasma physics, statistics of the galactic pulsar population, cosmology, gravitational wave sources). Here are some ongoing projects:
Too close for comfort: calculation of a supernova explosion in a tight binary. Neutron stars born in tight binary systems constitute some of the most intensively studied systems in astrophysics: low mass X-ray binaries and binary millisecond pulsars. The supernova event is known to be critical for the system's evolution: the mass loss and the explosive kick that yield the compact object dictate binary disruption or survival. Also important but not well-studied is the fate of the mass loosened from the companion. Numerical calculation of the hydrodynamic interaction of a supernova shock with a companion star elucidates how much falls back onto the neutron star and the companion. Accreted mass and angular momentum may have important consequences. I am curious about the possibilities that millisecond pulsars can be formed by late time accretion without going through the canonical low mass X-ray binary phase and that millisecond pulsars may be born with severely mauled companion stars or with no companion at all. The mass loss can also modify estimates for the masses of X-ray binary progenitor systems since the supernova-driven mass loss of the companion has not previously been taken into account. Finally, the inferred formation rate of black holes resulting from late time accretion may allow constraints on soft nuclear equations of state.
Cosmology and massive black holes: the intertwined merger history of holes and halos. Observations indicate massive black holes exist in the centers of many galaxies. Current theories of cosmological structure formation suggest bound entities undergo repeated mergers. Unless we live during a special epoch, central massive black holes were present when earlier sub-galactic structures merged and the holes were dragged to the common center by dynamical friction after the merger. I am interested in the dynamical processes that take place as several massive 10^3 M_sun holes interact with each other and with the background galaxies. The dynamical issues relevant to the hole interactions include the propensity for two compact members of a three body system to coalesce by gravitational wave emission or by direct collision; the propensity to eject one or more holes during a resonant three body encounter; the role of eccentricity evolution for driving coalescence; the momentum impulse given to a coalescing black hole pair. Such problems can be approached by an appropriate combination of analytic approximation and numerical computation. Answers can then be used to address more general questions: How does the number and distribution of masses of holes change as the Universe evolves? What evidence in the structure of galaxies (e.g. size of the core) can we use to shed light on the merger history of holes and halos?
Pulsars: what are the extreme limits for spin rate, translational velocity, and orbital period? Pulsars with the most rapid spin rates, the highest translational velocities and in the tightest binaries offer unique windows into physical regimes otherwise inaccessible to observation. These objects, ``fastest'' in each sense of the word, demark areas of physical significance in neutron star science: the critical spin period of a neutron star depends on the equation of state of neutron matter and the mass; the highest translation velocities are generated by a mechanism of unknown origin most likely associated with supernova collapse; and the tightest binaries damp by gravitational wave emission and may be used to test the predictions of general relativity and to infer precise values of compact star masses. Such binaries will eventually coalesce and illuminate the Universe in gamma-rays and gravitational waves. I am interested (with Jim Cordes) in developing and applying statistical inference tools to extract key elements of neutron star populations from radio pulsar surveys using all the available information. These elements include distributions of neutron stars in translational velocity, spin period and orbital period but extend to other important aspects of pulsars (luminosity, beaming fraction, birth rate, etc.). There are a variety of implications for the physics of neutron stars, for asymmetries of core collapse, and for understanding neutron star and neutron star-related populations, such as old accreting neutron stars, neutron star-black hole binaries, gamma-ray burst sources, and progenitors to radio pulsars, such as low-and-high mass X-ray binaries.
Grains: The chemistry of the biogenic elements is crucial in the development of life in our solar system. There appears to be a growing consensus that complex material from the interstellar medium (ISM) survived to be incorporated into the solar system. Understanding of the processes active in the ISM, especially those relevant to hydrogen, carbon, oxygen and nitrogen, are crucial to understanding the formation of the solar system and the pathway by which life emerged. An estimate of the interaction potential for atom with substrate and for atom with atom in the presence of substrate is key for answering questions like: do light atoms occupy the surface or the bulk sites of a grain in the ISM, how susceptible are they to being removed by radiation, by collisions, how quickly are they evaporated by thermal or quantum mechanical effects, and how quickly do they react with one and other? I am interested in the use of density-functional methods as a tool for making these estimates.
Selected Publications: -Chernoff, David F. F., and Martin D. Weinberg. "Evolution of Globular Clusters in the Galaxy." Ap. J. 351, 121 (1990).
-Djorgovski, S., G. Piotto, E. S. Phinney and D. F. Chernoff. "Modification of Stellar Populations in Post-Core-Collapse Globular Clusters." Ap. J. Letters 372, L41 (1991).
-Lenzuni, Paolo, David F. F. Chernoff, and E. E. Salpeter. "The Formation of Primordial Degenerate Protostars. " Ap. J. 393, 232 (1992).
-Chernoff, David F. F., and Lee Samuel Finn."Gravitational Radiation, Inspiraling Binaries, and Cosmology." Ap. J. Letters 411, L5 (1993).
-Kimoto, Paul A., and David F. F. Chernoff. "Convergence Properties of Finite Difference Hydrodynamic Schemes in the Presence of Shocks." Ap. J. Suppl. 96, 627 (1995).
