You may have never left the comfort of your home planet, but you probably know that galaxies are surrounded by a nearly spherical region of scattered stars. This is what’s known as the Galactic Halo, a vast domain that stretches out tens of thousands of light-years and contains stars, gas, and dark matter. The halo's dark matter is the glue that holds the galaxy together, a mysterious substance that eludes direct detection yet exerts a gravitational pull that shapes the cosmos.

As pretty as this phenomenon may be, it is the product of cannibalism. Take the Milky Way, for example. Over billions of years, our cosmic neighbourhood has gravitationally devoured and assimilated smaller satellite galaxies. As these galaxies were disrupted, their stars became part of our halo.