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Astronomy Colloquium

Wednesday, February 23, 2022
4:00pm to 5:00pm
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Online and In-Person Event
GraL: In Search of Quasar Gravitational Lenses from Gaia and Beyond
Alberto Krone-Martins, Lecturer, Donald Bren School of Information and Computer Sciences, University of California, Irvine,

What is the value of the Hubble constant? How does Dark Matter clump on small scales? Multiply imaged and gravitationally lensed QSOs are fundamental objects to help answer these questions, beyond being useful for a broad and diverse spectrum of research. However, these objects are very rare and elusive, with barely a few hundred currently known. The GraL group was created to tackle this issue and to discover and characterize new lensed QSOs profiting from the ESA/Gaia satellite's exceptional angular resolution. Gaia is expected to enable the creation of a magnitude-limited survey of such phenomena over the entire sky for the first time.

In this talk, I will present a brief overview of the major motivations behind our search for lensed Quasars. Then I will comment on some strategies that we created to search and confirm new multiply-imaged Quasars from Gaia astrometry and its synergies with time-resolved ground-based surveys, such as the Zwicky Transient Facility, and follow-up observations from telescopes as Keck. Our methodologies, which are continuously evolving, are based on a mixture of innovative signal-processing, statistical, and explainable machine learning approaches that keep humans on the decision loop, and have been particularly effective for small training sets. Finally, I will show some recently discovered lenses thanks to Gaia EDR3, and I will discuss the exciting prospects for the upcoming Gaia Data Releases and for the adoption of currently available Quantum Annealers.

To view this talk via YouTube, please visit:

For more information, please contact Jim Fuller by email at [email protected] or visit