This is true. Astronomers can either find jobs working by themselves on their own data, or have to find jobs working with groups of astronomers led by a senior Principle Investigator astronomer. In my case, I did my own data gathering and analysis for many projects of my own design. I also joined the NASA COBE project led by more senior astronomers and did a lot of work on other people's data, however, I was free to develop my own research projects using their ( COBE) data and published this under my own name and those of my collaborators. Astronomical research is complicated and there are many many different 'styles' of doing it that can change many times during your career.