The (astro-) physics departments in Bonn and Cologne focus on complementary research areas, together, they span almost the full range of modern physics: from astrophysics, statistical biophysics and condensed matter research to nuclear and particle physics, quantum optics and string theory. The two departments host three so-called clusters of excellence on particle physics, on astrophysics, and quantum physics. These are large, themed research centres inside German universities, funded through a national competition. 
Color meets flavor (link: https://www.color-meets-flavor.de/)
Dynaverse (link: https://dynaverse.astro.uni-koeln.de/)
ML4Q (link: https://ml4q.de/)

Both departments are also engaged in collaborations with international research groups worldwide. Research links and collaborations are established both in nuclear and hadron physics and in condensed matter physics with the Forschungszentrum Jülich and in astronomy/astrophysics with the Max-Planck Institute for Radio Astronomy.