Reimagining the Disk-Jet Connection in Hard State Black Holes

Our Milky Way Galaxy is home to hundreds of millions of black holes with masses of about 10 times that of the Sun, and the vast majority of these stellar mass black holes are expected to be found in binary systems with a companion star. The black hole often accretes matter from the companion star, releasing an enormous amount of energy, mostly in the form of X-rays; such systems are known as black hole X-ray binaries (BHXBs). Some BHXBs undergo outbursts that change the structure of the black hole accretion disk and produce relativistic jets of material. Researchers at the University of Nevada, Reno (UNR) through an interdisciplinary collaboration between astrophysics and computer science will analyze radio observations of 20 BHXB systems pre- and post-outburst to reveal the physical drivers for how jets respond to accretion flows. They will build a catalog of the systems that will be accessible through an interactive website. The survey will place stringent constraints on the Galactic BHXB population and thus our understanding of stellar populations. The project will contribute to the training of the next generation of scientists by including two graduate students in the research, as well as expanding an existing outreach program that will provide astronomy lessons to 1000 middle school students across Nevada. This project focuses on the hard X-ray state of BHXBs that occurs during the initial outburst triggered by thermal-viscous instabilities in their disks and during the return to quiescence at the end of the outburst cycle. As more BHXB outbursts have been monitored, more systems have been found to deviate from an expected radio/X-ray luminosity correlation, the slope of which reflects how jets respond to mass accretion. The physics driving this behavior is still debated, and one major limitation to the physical interpretation is that the current sample of hard state BHXBs is of heterogeneous quality with unaccounted systematics. The UNR researchers will address this limitation by producing a publicly available catalog that will include well defined quality control metrics, uniform procedures to calculate luminosities, and a rich set of features (e.g., spectral properties, orbital parameters, and outburst histories) to allow multi-dimensional analysis. They will then apply global statistical analyses to the ensembled dataset of all hard state/quiescent BHXBs to tease out the physical properties that most strongly correlate with a system’s behavior during an outburst. Finally, the researchers will use what is learned about the radio/X-ray luminosity correlation to perform an archival large-sky survey to discover new quiescent BHXB candidates in the Milky Way. 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.