Probing Accretion with Changing-Look Quasars
What is the nature of the extreme variability observed in changing-look quasars?
The discovery of changing-look quasars has challenged our understanding of accretion in active galactic nuclei. These accreting supermassive black holes exhibit extreme variability phenomena, especially in the appearance/disappearance of their broad emission lines in repeat optical spectroscopy (see video below). Surprisingly, these changes occur on short timescales of just a few years, a factor of 1,000 times faster than expected. Many observations have now suggested that the origin of this phenomenon is due to rapid changes in the accretion rate onto the central supermassive black hole (e.g., Ruan et al., 2016; 2019). Nevertheless, it is unclear how these dramatic changes could occur on timescales much shorter than predicted by our current understanding of black hole accretion.
An artists’s impression of the accretion flow around a supermassive black hole in a changing-look quasar. The accretion rate rapidly decreases, leading to a dramatic fading of the quasar. Overlaid are two epochs of optical spectra observed by SDSS, showing the dramatic changes in the spectra, and in particular the disappearance of the broad emission lines.
Animation credit: Dana Berry
My team is currently studying links between variable accretion phenomena in stellar mass black holes (in X-ray binary systems), massive black holes (in tidal disruption events), and supermassive black holes (in active galactic nuclei). We use observations from telescopes across the electromagnetic spectrum, including the Chandra X-ray Observatory, Hubble Space Telescope, the Swift Telescope, and an array of ground-based observatories. By modeling the spectral energy distribution of these accreting systems as they undergo dramatic variability, we aim to test whether accretion phenomena around black holes is scale-invariant.
Students: Virginia Marquez-Pacheco
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