Seeing Triple: the Multiply-imaged Standard Candle Supernova "H0pe" That Yielded a Value for the Current Expansion Rate of the Universe

Speaker: Brenda Frye (University of Arizona) In Person and zoom

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Einstein first correctly predicted how mass deflects light. Galaxy clusters, comprising of up to hundreds of galaxies all residing in a still larger dark matter halo, act as excellent gravitational lenses. We present results from the James Webb Space Telescope (JWST) Prime Extragalactic Areas and Reionization and Lensing Science (PEARLS) program targeting galaxy cluster lenses. One point-source situated behind the galaxy cluster PLCK G165.7+67.0 (G165) appeared in three different locations as a result of lensing effects. Follow-up observations confirmed this source to be a distant Type Ia supernovae (SN) at a redshift of 1.783 that we call "SN H0pe." Differences in the path length to each image give rise to different photon arrival times. These "time delays," together with a gravitational lensing model, return a value for the Hubble-Lemaître constant "H0." Under double-blinded protocols, two time delays were measured by a photometric approach and a rare spectroscopic approach, and seven lens models were constructed. The time delays were augmented by measurements of the three absolute magnifications. By a scaled fit of the predicted values for these five observables relative to the measured set, a best-fit value was inferred of H0 = 75.7(+8.1)(-5.5) km/s/Mpc. This is only the second time H0 has been measured for a lensed supernova, and the first time using a standard candle. Regular monitoring of G165 and other galaxy cluster fields with similar properties may be well-rewarded by the detection of additional strongly-lensed SNe useful for Cosmology.