David Chernoff

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 BlackHoles, Opacity of H- at High Density

Biography

David F. Chernoff has worked on a variety of topics (evolution of starclusters, collisionless and collisional stellar dynamics, plasmaphysics, 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 tightbinary. Neutron stars born in tight binary systems constitute some ofthe most intensively studied systems in astrophysics: low mass X-raybinaries and binary millisecond pulsars. The supernova event is knownto be critical for the system's evolution: the mass loss and theexplosive kick that yield the compact object dictate binary disruptionor survival. Also important but not well-studied is the fate of themass loosened from the companion. Numerical calculation of thehydrodynamic interaction of a supernova shock with a companion starelucidates how much falls back onto the neutron star and the companion.Accreted mass and angular momentum may have important consequences. Iam curious about the possibilities that millisecond pulsars can beformed by late time accretion without going through the canonical lowmass X-ray binary phase and that millisecond pulsars may be born withseverely mauled companion stars or with no companion at all. The massloss can also modify estimates for the masses of X-ray binaryprogenitor systems since the supernova-driven mass loss of thecompanion has not previously been taken into account. Finally, theinferred formation rate of black holes resulting from late timeaccretion may allow constraints on soft nuclear equations of state.

Cosmology and massive black holes: the intertwined merger history ofholes and halos. Observations indicate massive black holes exist in thecenters of many galaxies. Current theories of cosmological structureformation suggest bound entities undergo repeated mergers. Unless welive during a special epoch, central massive black holes were presentwhen earlier sub-galactic structures merged and the holes were draggedto the common center by dynamical friction after the merger. I aminterested in the dynamical processes that take place as severalmassive 10^3 M_sun holes interact with each other and with thebackground galaxies. The dynamical issues relevant to the holeinteractions include the propensity for two compact members of a threebody system to coalesce by gravitational wave emission or by directcollision; the propensity to eject one or more holes during a resonantthree body encounter; the role of eccentricity evolution for drivingcoalescence; the momentum impulse given to a coalescing black holepair. Such problems can be approached by an appropriate combination ofanalytic approximation and numerical computation. Answers can then beused to address more general questions: How does the number anddistribution of masses of holes change as the Universe evolves? Whatevidence in the structure of galaxies (e.g. size of the core) can weuse to shed light on the merger history of holes and halos?

Pulsars: what are the extreme limits for spin rate, translationalvelocity, and orbital period? Pulsars with the most rapid spin rates,the highest translational velocities and in the tightest binaries offerunique windows into physical regimes otherwise inaccessible toobservation. These objects, ''fastest'' in each sense of the word,demark areas of physical significance in neutron star science: thecritical spin period of a neutron star depends on the equation of stateof neutron matter and the mass; the highest translation velocities aregenerated by a mechanism of unknown origin most likely associated withsupernova collapse; and the tightest binaries damp by gravitationalwave emission and may be used to test the predictions of generalrelativity and to infer precise values of compact star masses. Suchbinaries will eventually coalesce and illuminate the Universe ingamma-rays and gravitational waves. I am interested (with Jim Cordes)in developing and applying statistical inference tools to extract keyelements of neutron star populations from radio pulsar surveys usingall the available information. These elements include distributions ofneutron stars in translational velocity, spin period and orbital periodbut extend to other important aspects of pulsars (luminosity, beamingfraction, birth rate, etc.). There are a variety of implications forthe physics of neutron stars, for asymmetries of core collapse, and forunderstanding neutron star and neutron star-related populations, suchas old accreting neutron stars, neutron star-black hole binaries,gamma-ray burst sources, and progenitors to radio pulsars, such aslow-and-high mass X-ray binaries.

Grains: The chemistry of the biogenic elements is crucial in thedevelopment of life in our solar system. There appears to be a growingconsensus that complex material from the interstellar medium (ISM)survived to be incorporated into the solar system. Understanding of theprocesses active in the ISM, especially those relevant to hydrogen,carbon, oxygen and nitrogen, are crucial to understanding the formationof the solar system and the pathway by which life emerged. An estimateof the interaction potential for atom with substrate and for atom withatom 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 theISM, how susceptible are they to being removed by radiation, bycollisions, how quickly are they evaporated by thermal or quantummechanical effects, and how quickly do they react with one and other? Iam interested in the use of density-functional methods as a tool formaking 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).