It’s summer hear (28-30°C) and heat and CMOS sensors don’t get along well for noise when you are imaging dark things, like the night sky. So this is the “worst case scenario” for using uncooled sensors. Normally I don’t Image because the noise makes my images unusable from my older cameras.
The Z6 (and maybe the Z7… if it was a tad cooler) does a fantastic job, see attached photos, and while a temperature controlled cooled camera does better (especially monochromic with Narrowband filters) these results are pretty impressive.
The Z6 is a nice all around camera but it does have its drawbacks (uncooled, OSC so no Narrowband, and it cannot be directly powered by the USB for long nights so at some point you need to physically swap out batteries). Minor points be. Buying a camera for astrophotography, but worth mentioning.
If you want to give it a try yourself, ISO800 seems to be the sweet spot if you are tracking the sky, if you are static tripod, iso8000 is usable but you’ll want to get 4x the exposure or only focus on really bright objects that would saturate the filter quickly; like M42 – Orion Nebula or planets.
There is the 500x rule if you are imaging on a static tripod (500 / focal length = exposure in seconds) however with 24MP sensor I would suggest using 300 instead of 500 to avoid blur in the pixels from star movements, and even 200 if you are trying with a Nikon Z6 or whatever new massive megapixel camera Nikon comes out with next Z8/Z9?