Dark Nebula
Throughout known space there are areas, often tens of parsecs across known as dark nebulae. These represent accretions of gravitic anomalies. Whilst it is still possible to transit Dark Nebulae through hyperspace, there is a small but measurable probability of a drive failure. Systems located within dark nebulae are sometimes colonised, even given this risk.
During the First Exterminator War it was theorised that the new enemy might have somehow originated in dark nebulae. This theory was quickly discounted.
Dark nebulae are also characterised by dangerous spacial anomalies, which are, fortunately rare and nowhere near systems of interest to humanity and therefore regarded as a negligible risk to navigation.