Is it a good idea to explore other field of research when you are sure of your interested area?

Question

I am currently pursuing master's in Physics. In my university, there aren't many professors in my field of interest i.e. Astrophysics, the professors whose work I was interested in, declined me the project cause I asked them late. So, I joined another professor, telling him that I am interested in Astrophysics and want to do project in Fluid Dynamics. He accepted and offered me one, that have application of fluid dynamics in biophysics. I thought this since fluid dynamics is used in Astrophysics studies as well, and in my topic of interest i.e. star formation and galaxy dynamics.

Now, I am pretty sure for now, I want to go into Astrophysics. My question is for higher studies what ways could doing a master's thesis in a topic other than interest, hinder my chances of getting PhD admission?

If cons, what could I do to improve my chances?

And if pros, please list them.

I started my project a month ago.

Answer 1

You have been wise to be a bit flexible, yielding to circumstances. If you do well in your current work and maintain flexibility going forward you will probably continue to do well.

When it comes time to apply for doctoral programs, don't be so insistent on a narrow field (though "astrophysics" is broad enough, though "star formation" seems narrow to me, a non expert) that you limit your chances. If the program you are in gives you the research skills applicable to a variety of fields then you are in a good position. You can, over a career, change your research direction.

But you have to do well along the way and be in a position where supervisors are willing to support your future plans.