James Webb Space Telescope Feed Post

Arxiv: SN H0pe: The First Measurement of H_0 from a Multiply-Imaged Type Ia Supernova, Discovered by JWST Published: 3/27/2024 8:00:08 PM Updated: 3/27/2024 8:00:08 PM

Paper abstract: The first James Webb Space Telescope ({\it JWST}) Near InfraRed Camera(NIRCam) imaging in the field of the galaxy cluster PLCK G165.7+67.0 (z=0.35)uncovered a Type Ia supernova (SN~Ia) at z=1.78, called ``SN H0pe." Threedifferent images of this one SN were detected as a result of stronggravitational lensing, each one traversing a different path in spacetime,thereby inducing a relative delay in the arrival of each image. Follow-up {\itJWST} observations of all three SN images enabled photometric and rarespectroscopic measurements of the two relative time delays. Following strictblinding protocols which oversaw a live unblinding and regulatedpost-unblinding changes, these two measured time delays were compared to thepredictions of seven independently constructed cluster lens models to measure avalue for the Hubble constant, H_0=71.8^{+9.8}_{-7.6}~km~s^{-1}~Mpc^{-1}.The range of admissible H_0 values predicted across the lens models limitsfurther precision, reflecting the well-known degeneracies between lens modelconstraints and time delays. It has long been theorized that a way forward isto leverage a standard candle, however this has not been realized until now.For the first time, the lens models are evaluated by their agreement with theSN absolute magnification, breaking these degeneracies and producing our bestestimate, H_0=75.4^{+8.1}_{-5.5}~km~s^{-1}~Mpc^{-1}. This is the firstprecision measurement of H_0 from a multiply-imaged SN~Ia, and provides ameasurement in a rarely utilized redshift regime. This result agrees with otherlocal universe measurements, yet exceeds the value of H_0 derived from theearly Universe with \gtrsim90\% confidence, increasing evidence of the Hubbletension. With the precision provided by only four more events, this approachcould solidify this disagreement to >3\sigma.