NASA ASTRA White Paper: A Chandra Successor in the 2030s

Chandra established that soft X-ray spectral imaging with approximately 1 arcsec angular resolution is an essential tool for almost every area of astrophysics, from the early Universe to ice chemistry in protoplanetary disks. While Chandra continues to deliver groundbreaking science, it lacks the sensitivity to be the counterpart to JWST, Roman, Rubin, LISA, ngVLA, ALMA, IceCube, NewAthena, ELT, and other upcoming large facilities. Here we highlight the scientific potential of a Chandra successor with >10x higher sensitivity and >50x survey speed. While the scientific reach of such a mission is very broad, we showcase four high-priority science questions that require these capabilities -- How did supermassive black holes form?, How does stellar and AGN feedback work in galaxies?, How does high-energy stellar activity affect exoplanet atmospheres? and, How do black holes merge? A Chandra successor in the 2030s would also demonstrate the X-ray mirror technology for a future flagship and sustain the US high energy astrophysics workforce until that flagship launches. We outline the science-instrument trade space by sketching three missions based on the NASA Probe concept study report for the Advanced X-ray Imaging Satellite (AXIS): AXIS-Deep, AXIS-Classic, and AXIS-Fast, highlighting a breakthrough science case for each and listing others that drive the design.