# A 3.5-million Solar Masses Black Hole in the Centre of the Ultracompact Dwarf Galaxy Fornax UCD3

**Authors:** Anton V. Afanasiev, Igor V. Chilingarian, Steffen Mieske, Karina T. Voggel, Arianna Picotti, Michael Hilker, Anil Seth, Nadine Neumayer, Matthias Frank, Aaron J. Romanowsky, George Hau, Holger Baumgardt, Christopher Ahn, Jay Strader, Mark den Brok, Richard McDermid, Lee Spitler, Jean Brodie, Jonelle L. Walsh  
**arXiv:** [1804.02938](https://arxiv.org/abs/1804.02938)  
**Date:** 2018-04-09  
**Summary page:** https://www.summarizepaper.com/en/paper/1804.02938v1/

## Key points

- Astronomers have detected a supermassive black hole in the centre of the ultracompact dwarf galaxy Fornax UCD3
- This is the fourth such black hole found in an ultracompact dwarf galaxy and the first one in the Fornax cluster
- Recent discoveries of central supermassive black holes provide support for the tidal stripping hypothesis regarding the origin of these galaxies
- Some massive UCDs might be representatives of the high luminosity tail of the globular cluster luminosity function on statistical grounds
- The detection was made using isotropic Jeans dynamical modelling with internal kinematics derived from adaptive optics assisted observations with SINFONI spectrograph and seeing limited data collected with FLAMES spectrograph at ESO VLT
- UCD3 hosts metal-rich stars enhanced in α-elements that supports tidal stripping as its likely formation scenario
- Up to 80% of luminous UCDs in galaxy clusters host central black holes, while this fraction should be lower for UCDs in groups because their progenitors are more likely to be dwarf galaxies which do not tend to host central black holes.

## Summary

Astronomers have detected a supermassive black hole in the centre of the ultracompact dwarf galaxy Fornax UCD3, which corresponds to 4% of its stellar mass. This is the fourth such black hole found in an ultracompact dwarf galaxy and the first one in the Fornax cluster. The origin of these galaxies remains a matter of debate, but recent discoveries of central supermassive black holes provide support for the tidal stripping hypothesis. On statistical grounds, some massive UCDs might be representatives of the high luminosity tail of the globular cluster luminosity function. The detection was made using isotropic Jeans dynamical modelling with internal kinematics derived from adaptive optics assisted observations with the SINFONI spectrograph and seeing limited data collected with the FLAMES spectrograph at ESO VLT. The team ruled out zero black hole mass at a 3σ confidence level when adopting a mass-to-light ratio inferred from stellar populations. Similarly to other known UCDs that harbour black holes, UCD3 hosts metal-rich stars enhanced in α-elements that supports tidal stripping as its likely formation scenario. The team estimates that up to 80% of luminous UCDs in galaxy clusters host central black holes, while this fraction should be lower for UCDs in groups because their progenitors are more likely to be dwarf galaxies which do not tend to host central black holes.