Binary Accretion

Purdue University, West Lafayette IN

Investigators

Abstract

A research team at Purdue University will investigate the interaction and long-term evolution of astrophysical binary systems with the disks of matter surrounding them. A “binary” here refers to any system of two gravitating astrophysical objects in a bound orbit. This includes everything from stars and their compact end-states (white dwarfs, neutron stars, and black holes) to supermassive black hole binaries (SMBHBs), which are predicted to exist at the cores of recently-merged galaxies. Binaries are important to several core fields of astrophysics, and they are commonly found in the vicinity of a significant quantity of gas, which accretes onto the binary via a circumbinary disk. Describing the evolution of a binary plus disk system requires understanding both the hydrodynamical reaction of the disk to the binary’s orbital motion, and the evolution of the binary orbit and component masses in response to the disk accretion. The principal investigator will support and mentor a graduate student in this work and will strive to involve students from groups under-represented in astronomy and astrophysics The investigators will perform a comprehensive suite of two- and three- dimensional magneto-hydrodynamic and hydrodynamical simulations of a binary interacting with a gas disk. The work will address several fundamental open questions: (i) Do disk torques on the binary drive the binary components together, or apart? (ii) Does interaction with a disk make the binary orbit more or less eccentric? (iii) Does the accretion always drive the binary towards equal-mass? (iv) How much gas is typically very close to the binary, and how much does this nearby gas contribute to the emissivity of the accretion disk? (v) What is the impact of the circumbinary gas on gravitational wave measurements for black holes, and on binary populations for stars, neutron stars, and white dwarfs? (vi) How do all of the above questions depend on the binary orbital parameters and mass ratio, and on the disk properties? As a product of the research, the researchers will create a Binary Evolution and Light-curve Library, which is needed to interpret a broad range of electromagnetic and gravitational wave observations. This project advances the goals of the NSF Windows on the Universe Big Idea. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.