Astro2020 Science White Paper: The Local Relics of of Supermassive Black Hole Seeds

Understand

We have compelling evidence for stellar-mass black holes (BHs) of ~5-80 M_sun that form through the death of massive stars.

• We also have compelling evidence for so-called supermassive BHs (10^5-10^10 M_sun) that are predominantly found in the centers of galaxies.
• We have very good reason to believe there must be BHs with masses in the gap between these ranges: the first ~10^9 M_sun BHs are observed only hundreds of millions of years after the Big Bang, and all theoretically viable paths to making supermassive BHs require a stage of "intermediate" mass.
• However, no BHs have yet been reliably detected in the 100-10}^5 M_sun mass range.