Gravity is a pretty reliable signal; doesn't decay much on million-years scale, and doesn't get obscure much either. Not to imply those were from unnatural pro

Gravity is a pretty reliable signal; doesn't decay much on million-years scale, and doesn't get obscure much either. Not to imply those were from unnatural processes, more to indicate that basic spacefaring technology implies ability to detect such: https://en.wikipedia.org/wiki/Mass_concentration_(astronomy) https://en.wikipedia.org/wiki/Mass_concentration_(astronomy)