RUBIES Reveals a Massive Quiescent Galaxy at <i>z</i>=7.3

We report the spectroscopic discovery of a massive quiescent galaxy at z(spec) = 7.29 +/- 0.01, just similar to 700 Myr after the big bang. RUBIES-UDS-QG-z7 was selected from public JWST/NIRCam and MIRI imaging from the PRIMER survey and observed with JWST/NIRSpec as part of RUBIES. The NIRSpec/PRISM spectrum reveals one of the strongest Balmer breaks observed thus far at z > 6, with no emission lines but tentative Balmer and Ca absorption features, as well as a Lyman break. Simultaneous modeling of the NIRSpec/PRISM spectrum and NIRCam and MIRI photometry (spanning 0.9-18 mu m) shows that the galaxy formed a stellar mass of log(M & lowast;/M-circle dot)=10.23(-0.04)(+0.04 )before z similar to 8 and ceased forming stars 50-100 Myr prior to the time of observation, resulting in log(sSFR/Gyr-1) 7. The discovery of RUBIES-UDS-QG-z7 has strong implications for galaxy formation models: the estimated number density of quiescent galaxies at z similar to 7 is >100 x larger than predicted from any model to date, indicating that quiescent galaxies have formed earlier than previously expected