Interstellar medium

The space between the stars isn't empty. It's filled with gas and dust — the raw material of the next generation of stars, and the repository of everything previous generations have returned. When we look at a star's spectrum, the interstellar medium leaves its own marks on the light along the way, and those marks are both a nuisance to be modelled and a signal to be mined.

I'm interested in what the interstellar medium can tell us when we study it at scale across many sightlines. One long-standing puzzle is the diffuse interstellar bands — hundreds of absorption features whose carriers, after a century of study, are still largely unidentified. Large spectroscopic surveys give us millions of sightlines through the Galaxy, which turns this into a data problem we can actually attack.

What I find compelling here:

• Can we use enormous spectroscopic datasets to map interstellar absorption in three dimensions across the Galaxy?
• What are the carriers of the diffuse interstellar bands, and what do they trace?
• How do we cleanly separate the interstellar signal from the stellar one, so each can be modelled properly?