Everything we see in the universe is a snapshot of the past: As light takes its time to reach our telescopes, the system we’re observing continues to evolve, and what we end up seeing is a moment in its history. By revisiting an object over the course of decades, we can look not only into its past, but can watch its history unfold.
Eleven years after it was last observed and 17 years after a stellar merger occurred, SOFIA looked at V838 Monocerotis, or V838 Mon, a binary star system about 19 thousand light-years away from Earth, capturing a snapshot in time of its makeup. This confirmed that the dust chemistry of the system has changed significantly over the course of nearly two decades following the merger, particularly over the past decade. This provided a history we otherwise cannot look at and offered an archaeological view of its evolution.
— Read on blogs.nasa.gov/sofia/2021/12/17/a-stellar-mergers-snapshot-in-time/