SN Helios at z=3.34 enables first time-delay H0 measurement beyond redshift 3 via cluster lensing

The discovery used NIRCam F150W-dropout selection in VENUS survey data from July 2026, followed by NIRSpec prism spectroscopy showing resolved H-alpha emission and P-Cygni absorption at z=3.34. Template matching and light-curve comparison to local Type II events place the event at 27.5 plus or minus 2.8 rest-frame days past maximum. Cluster lens models from independent teams yield magnifications of 10-20 and forecast a second image within 2-6 years, enabling time-delay cosmography at unprecedented redshift.

Prior lensed supernovae reached only z less than 2, limiting leverage on dark-energy evolution at early epochs. SN Helios demonstrates that ultra-faint, heavily obscured hosts can host core-collapse events missed by blank-field surveys, raising the inferred rate per unit star formation in low-mass galaxies. The spectrum also supplies an empirical SED template to reject z approximately 16 Lyman-break galaxy contaminants that lack multi-epoch data.

The principal limitation is the single-epoch light curve and model-dependent time-delay prediction; a measured delay would require at least two additional imaging epochs spaced by months. Confirmation of the second image would directly test whether H0 inferences remain consistent when the source redshift exceeds 3, tightening constraints on early dark energy or new physics.