outstanding questions of the Universe's structure formation. It will also provide transformative
new observing capabilities for every area of astrophysics, and to heliophysics and planetary
physics as well. LEM's main goal is a comprehensive look at the physics of galaxy formation,
including stellar and black-hole feedback and flows of baryonic matter into and out of
galaxies. These processes are best studied in X-rays, and emission-line mapping is the …