# Strong Constraints on Dark Matter Annihilation in Ursa Major III/UNIONS 1

**Authors:** Milena Crnogorčević, Tim Linden  
**arXiv:** [2311.14611](https://arxiv.org/abs/2311.14611)  
**Date:** 2023-11-24  
**Summary page:** https://www.summarizepaper.com/en/paper/2311.14611v1/

## Key points

- Ursa Major III is the faintest satellite galaxy ever observed
- It is believed to be highly dominated by dark matter if in equilibrium
- Ursa Major III may be an ideal target for dark matter indirect detection searches
- No excess gamma-ray emission was found from Ursa Major III using Fermi-LAT data
- High J-factor of Ursa Major III would rule out standard thermal dark matter annihilation to b-bar final states for dark matter masses up to 4 TeV
- Near-future data could provide transformative constraints on thermal dark matter through optical observations and spectroscopic measurements
- The research builds upon previous work in the field and sets a foundation for further exploration into understanding dark matter
- Identification and analysis of Ursa Major III provides valuable insights into our understanding of dark matter
- Constraints set on dark matter annihilation contribute to ongoing efforts to unravel the mysteries surrounding thermal dark matter

## Summary

The discovery of Ursa Major III and other similar high J-factor systems opens up exciting possibilities for future studies in the field of thermal dark matter. A recent study has identified this satellite galaxy as the faintest system of its kind ever observed. Based on dynamical considerations, it is believed that if the system is in equilibrium, it is likely to be highly dominated by dark matter. This, combined with its proximity, suggests that Ursa Major III may be an ideal target for dark matter indirect detection searches. To investigate this further, the researchers utilized 15 years of Fermi-LAT data to search for gamma-ray emission from Ursa Major III. However, no excess was found, leading to the establishment of strong constraints on dark matter annihilation. Interestingly, if the high J-factor (a measure of dark matter density) of Ursa Major III is confirmed, it would rule out standard thermal dark matter annihilation to b-bar final states for dark matter masses up to 4 TeV. These findings suggest that near-future data could potentially provide transformative constraints on thermal dark matter through optical observations and spectroscopic measurements of extreme dark matter targets. The research builds upon previous work in this area [1-11] and sets a foundation for further exploration into understanding the nature and properties of dark matter. In conclusion, the identification and analysis of Ursa Major III as a potential dwarf spheroidal galaxy target for dark matter indirect detection searches provides valuable insights into our understanding of dark matter. The constraints set on dark matter annihilation based on Fermi-LAT data contribute to ongoing efforts to unravel the mysteries surrounding thermal dark matter. With future advancements in observational techniques and measurements, we may gain transformative insights into the nature of dark matter and its role in the universe.