# Roman CCS White Paper: Characterizing the Galactic population of isolated black holes

**Authors:** Casey Y. Lam, Natasha Abrams, Jeff Andrews, Etienne Bachelet, Arash Bahramian, David Bennett, Valerio Bozza, Floor Broekgaarden, Sukanya Chakrabarti, William Dawson, Kareem El-Badry, Maya Fishbach, Giacomo Fragione, Scott Gaudi, Abhimat Gautam, Ryosuke Hirai, Daniel Holz, Matthew Hosek Jr., Macy Huston, Tharindu Jayasinghe  
**arXiv:** [2306.12514](https://arxiv.org/abs/2306.12514)  
**Date:** 2023-06-21  
**Summary page:** https://www.summarizepaper.com/en/paper/2306.12514v2/

## Key points

- Existing summary highlights uncertainty surrounding properties of isolated black holes (BHs) in the Milky Way
- Estimated 100 million BHs in our galaxy, but only one discovered so far
- Galactic Bulge Time Domain Survey offers opportunity to expand BH catalog by orders of magnitude
- Crucial to realize Roman's astrometric potential for accurate measurements and identification of BH candidates
- Minimize observational gaps in Bulge region, expected to host significant number of BHs
- Ground-based facilities can fill observational gaps during non-Bulge seasons with targeted observations
- Expanding catalog of isolated BHs has implications for massive stellar evolution, gravitational wave sources, supernova physics, and growth mechanisms of supermassive black holes
- Leveraging Roman's capabilities and combining with ground-based observations can significantly expand understanding of isolated black holes in the Milky Way

## Summary

The existing summary highlights the significant uncertainty surrounding the properties of isolated black holes (BHs) in the Milky Way. While there are estimated to be 100 million BHs in our galaxy, only one has been discovered so far. To address this knowledge gap, the Galactic Bulge Time Domain Survey offers a unique opportunity to expand the catalog of BHs by orders of magnitude in the coming decades. To achieve this goal, several key factors need to be considered. First, it is crucial to fully realize Roman's astrometric potential in both observation strategy and software pipelines. This will enable more accurate measurements and identification of BH candidates. Additionally, efforts should be made to minimize observational gaps of the Bulge region which is expected to host a significant number of BHs. Furthermore, ground-based facilities can play a vital role in filling in observational gaps during non-Bulge seasons by conducting targeted observations of the Bulge. Expanding the catalog of isolated BHs will have far-reaching implications for various areas of astrophysics; providing valuable insights into massive stellar evolution, shedding light on the origins of gravitational wave sources, enhancing our understanding of supernova physics and contributing to our knowledge about the growth mechanisms of supermassive black holes. In conclusion, by leveraging Roman's capabilities and combining them with ground-based observations scientists have an unprecedented opportunity to significantly expand our understanding of isolated black holes in the Milky Way; unlocking new avenues for exploring fundamental questions in astrophysics.