Which galaxy has the least stars per unit volume?
Abell 0194 (A194) or NGC 6822
After an intensive research on this strange topic, I found two probable answer to your questions. The link to the site is here. The link to referenced sources/studies are contained within the source website.
There is something out there called the mass-luminosity relation/mass-light ratio, which is the ratio of a galaxy's mass to the amount of light it emits (absolute magnitude). It is abbreviated as
So, we can assume this is the most reliable way to measure the number of stars in a galaxy to its volume. Since it is not easy to accurately estimate the number of stars and volume of a galaxy, especially if they are very far away.
In a paper published by Chincarini & Rood (1975), it states that the galaxy A194 has a
However, I then found a table, also regarding the matter of mass to luminosity ratio. At the bottom of the table, it listed a galaxy called N6822, which is Barnard's galaxy. It has an astounding
I am very unsure of such vague response, if anyone has reliable sources or answer, it would be great for everyone to check it out.