The Junkstorm is one of several known regions in the galaxy where higher-dimensional suffer from some kind of high-dim maelstrom. The exact nature of these maelstroms has not yet been discovered, at least not by humans. And not for lack of trying. Billions are poured each year across human space into research towards artificially creating these conditions.
Because in these regions, humans can live in relative peace as the higher-dimensional aliens avoid them. Much of the time, they not only do not settle there, but also do not cross it in spaceships, not even when traveling in hyperspace.
The Junkstorm is one of the smaller such regions. It can be found a few hundred light years away from Earth, in the same spiral arm of the galaxy. There are twenty star systems in the Junkstorm, with sixteen of them having planets. Of those slightly over a hundred planets, five are habitable. Three of them are actually inhabited. Colonization of a fourth has started.
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The precise effects of the Junkstorm on higher dimensional aliens is another secret that humans have not yet uncovered. The aliens thus affected have not shared details with humanity. What is known is that at the very least they experience discomfort and consider the Junkstorm as inhospitable. It is generally assumed that this discomfort turns into health being negatively affected over time. It is also widely known that the aliens can live and function within the Junkstorm for a limited time. Hours definitely, some of them for days or even weeks.
The Junkstorm does not seem to have a negative impact on humans, and probably not on any of the other low-dim races in the galaxy.
The Junkstorm does not have a sharp boundary. Towards its edge, the effect slowly abates, and the border region is estimated at several light years thick.
The vast majority of humanity lives in bubbles like the Junkstorm, where they do not compete with aliens superior in technology or abilities.