Collaborative Research: WoU-MMA: The Benchmark Measurement of Quasar Spectroscopic Variability and Implications for Supermassive Black Hole Binaries and Changing-Look Quasars

Most, if not all, reasonably massive galaxies host supermassive black holes in their centers, with masses of millions to billions of times the mass of the Sun. The most luminous non-exploding objects in the Universe, quasars are the result of gas falling onto these supermassive black holes and they can outshine all of the stars in their host galaxy. They are important because they appear to play a key role in shaping how galaxies came to look the way that they do today. However, because of their large cosmological distances, they appear as pinpricks of light on the sky and we cannot spatially separate the environment around the black hole to study its characteristics. Fortunately, quasars are intrinsically variable with frequent changes in brightness, making time-domain observations a powerful tool in revealing their central regions, akin to using a movie to tell a story instead of a single photograph. The research team at Vanderbilt and Penn State Universities will leverage these brightness changes and big data techniques to make the first measurement of how gas around supermassive black holes moves over a timescale of years to a decade. This will enable searches for exotic sources, like supermassive black holes in binary (SBHB) systems which have never been detected before, and changing-look quasars (CLQs) which turn on and off much faster than theory can explain. The investigators will also conduct a three-day data mining workshop for students in the Fisk-Vanderbilt Bridge Program and develop a series of introductory astronomy exercises using the popular Zooniverse interface.This project will constitute the benchmark measurement of multi-year quasar spectroscopic variability and apply it to searches for SBHBs and CLQs. This work will use a sample of approximately 5000 quasars from the Sloan Digital Sky Survey that have been observed spectroscopically more than once to measure the parameters of the broad H-beta line and their variability over times scales of 1-18 years. These will be used to define a statistical model for regular quasar variability, appropriate for many applications, including searches for SBHBs and CLQs. With this statistical tool the team will (a) compare the ensemble variability properties of SBHB candidates to a control sample for the first time, (b) test the nature of the best sub-pc separation SBHB candidates, (c) predict the necessary duration for SBHB monitoring campaigns to bear fruit, (d) constrain the masses that SBHB candidates can have, (e) determine for the first time whether CLQs represent extreme examples of normal quasar variability or a distinct phenomenon, and (f) define the CLQ class rigorously and quantitatively.This award addresses and advances the goals of the 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.