So far, you've only talked about what you want to STUDY. Not once did you describe what you intend to pursue as a CAREER.
What you want to study is a means to get to an end, which is what you wish to work in. You somehow are putting more emphasis in the means rather than the end.
So step back a bit and describe what you wish to pursue as a career.
If you want to have a career in Astronomy or Physics, then the best chance in having that is to have a PhD in Astronomy or in Physics. While there have been people with different majors entering PhD programs in Astronomy and Physics, they have a significantly more work to do to catch up with students who have already majored in those areas at the undergraduate level.
I do not know what "B.Tech" degree is equivalent to. Here, in the US, a "Bachelor of Science" in "Engineering Technology" is not equivalent to an engineering degree.
I have written already on a simple, first-order self-test that anyone with a different degree can try to see if one has the necessary background and preparation to be successful in a PhD or graduate program in physics here in the US:
https://www.physicsforums.com/threa...if-my-bachelors-degree-isnt-in-physics.64966/
Zz.