Help me choose a domain

I am 2nd year engineering student from an IIT pursuing CSE + EE. I have always had an interest in aerospace and astrophysics. During my DSA prep for the upcoming 2027 summer intern season, sometimes I question myself whether this is not my cup of tea, not sure whether this is a part of the journey ?!. what should I do, I need a clarity. should I focus on CS and try getting placed as a software or Embedded engineer. Or should I pursue Phd focusing on my past interest astrophysics or aerospace. I am also destined that I will definitely contribute to the aersospace industry using my CS degree if I could not pursue Phd, but the problem is the packages offered are too low for aerospace startups or even ISRO in India. If you guys suggest me taking a Phd which domain should I choose. I have no Idea how people choose a Phd domain, like how do you guys figure it out and what is the process for applying to the Phd abroad.