Noob physics question: I assume this talks about stars close enough that we can receive their light. Can we say anything about the number of stars & galaxies that are further away than that?
"The cosmic optical background (COB) is the average flux of visible light photons averaged over the volume of the observable Universe. It reflects, at least in part, an integral over the cosmological history of star formation occurring in recognizable galaxies, proto-galaxies, and star clusters (Conselice et al. 2016), as well as mass accretion by black holes (BHs) associated with the systems." - https://arxiv.org/abs/2011.03052v2
A common problem in astronomy is the lack of ways to measure things (we can't travel to the stars, yet). The special thing about this result is that it is a very direct and independent measurement of the background optical light in the Universe. This means it can be used to put independent constraints on the star formation history, as well as black hole accretion, and perhaps things we haven't even thought about yet.
Edit: And all those results are model dependent as everything else.
The biggest source of uncertainty with the new estimate is modeling of background light of our galaxy. Too bad that we cannot yet send a probe outside it to measure things directly.
Might be drastically more, or even less.
The main thing that is being presumed is the "big bang". If you proscribe to believing in the big bang, then the entirety of everything we see is an expansion from a single dense explosion of matter.
It is still a valid theory but I myself don't understand the physics of what is observed well enough to be convinced this is true. I believe that they are seeing something similar enough that it could be perhaps a "localized bang" or something like that.
The main evidence used as "proof" of the big bang is the observed data seeming to show that the everything in the universe is "dispersing" slowly. That is at least what I've heard claimed.