Nucleosynthesis and electromagnetic outcome from compact object mergers and their legacy

In the last decade, gravitational waves and multi-messenger time-domain astronomy provides a fresh view of the dynamic Universe and precursor a new era in astrophysics. Notably, it sheds light on the astrophysics of compact objects, the origin of the heaviest elements, and allows for unique probes of fundamental physics. Those heavy elements produced via the rapid neutron capture process have remained a question of intense debate for many years. A fresh example event is the "kilonova" emission that accompanied GW170817 revealed a binary neutron star merger. I will discuss recent results on the binary neutron stars simulation and how other explosive transient like the collapse of massive rotating stars "collapsars" which give rise to long GRBs and the formation of heavy elements in the universe. In particular, I will focus on two frontier research areas- neutron star mergers and collapsar (/massive- collapsar). Also, highlight how multi-messenger astronomy may answer how does the Universe create the heaviest elements?