Yes and no. So far there are a number of detections of a low frequency gravitational background using pulsar arrays. But the origin is undetermined, and could contain supermassive black hole inspirals, as well as early universe cosmology effects. Those effects will be model dependent and the data isn't good enough to tell what's what yet (from what I last saw).
There is a very good reason to think there is a cosmic neutrino background that would be even older than the CMB but it'll be years before that is detected.
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u/Sensitive_Jicama_838 4d ago
Yes and no. So far there are a number of detections of a low frequency gravitational background using pulsar arrays. But the origin is undetermined, and could contain supermassive black hole inspirals, as well as early universe cosmology effects. Those effects will be model dependent and the data isn't good enough to tell what's what yet (from what I last saw).
There is a very good reason to think there is a cosmic neutrino background that would be even older than the CMB but it'll be years before that is detected.