At https://phys.org/news/2019-11-voyager-interstellar-space-scientists-plas… … interstellar space – scientists detect plasma density jump as Voyager 2 moved from the solar system to beyond. The inference is that outer space has a higher density level of plasma – or that is the thinking of researchers in a paper in Nature Astronomy (Nov 2019) – although one might argue it is the bubble around the solar system that is dense (I suppose). There is definitely a boundary at the outer reaches of the solar system – as experienced somewhat earlier when Voyager 1 passed through. The boundary is approximately 11 billion miles away from the Sun.
At https://phys.org/news/2019-11-years-voyager-interstellar-space.html … we have more on the same story of the passage through the heliosphere. See also https://nature.com/articles/s41550-019-0928-3 … and https://doi.org/10.1038/s41550-019-0929-2 … and https://nature.com/articles/s41550-019-0918-5 etc). See also another one on the same subject at https://phys.org/news/2019-11-voyager-illuminates-boundary-interstellar-…