Simulated Arrakihs mock image of a galaxy halo

This simulated image shows ‘low surface brightness’ structures in the halo surrounding a Milky-Way-like galaxy. These structures look like faintly glowing arcs spreading outwards from the galaxy's central disc.  

Importantly, the structure of a galaxy’s halo can reveal a lot about how the galaxy formed. For example, stellar streams such as the arcs shown here are the remnants of smaller galaxies or star clusters that were torn apart while merging with the host galaxy.  

ESA's Arrakihs mission plans to study the stellar haloes of at least 80 nearby galaxies with a similar mass to our own. This is a large enough number to get statistics on how a ‘typical’ galaxy forms, allowing us to understand how unique our home galaxy is.  

[Image description: A blue-white, circular spiral galaxy is shown on a colourful starry background. Two faint, cloud-like arcs extend from the galaxy's central disc: one U-shaped loop sticks out to the lower left, and a larger hook-shaped arc extends up and to the left. A diffusely glowing oval-shaped dwarf galaxy lies to the left of the larger galaxy.]