Hello Gawtham!

You are extremely ambitious! Astrophysics will be a particular subject that you can pursue at post graduation level and not at undergraduation level. And IISERs/NISER/CEBS/IISc/IACS will be the best pick of institutions to choose for your undergraduate degree. You can also attempt to try for IIST(Indian Institute of Space Science and Technology), Trivandrum as it is a special institute for astronomy and astrophysics related reserach.

First step to become a astrophysicist is to take up the most suitable UG course, which would be BS-MS integrated Physics at IISERs or IACS, or BS Physical sciences at IISc or Integrated MSc Physical sciences at NISER or CEBS. After completing of your BS-MS course, you can go for Integrated PhD or M.Tech in astrophysics directly in IISERs/IACS/IITs itself or universities abroad. You can get into top institutions in India for astrophysics by qualifying in JEST or GATE. Some best colleges for MSc Astrophysics in India are:-

• Homi Bhabha National Institute, Mumbai
• Aryabhatta Research Institute of Observational Sciences, Nainital
• Harish-Chandra Research Institute, Allahabad
• Indian Institute of Astrophysics, Bangalore
• Indira Gandhi Centre for Atomic Research, Kalpakkam
• International centre for theoretical sciences (TIFR), Bangalore
• Indian Institute of Science, Bangalore
• The IISERs(Bhopal, Thiruvananthapuram,Pune,Mohali)
• Instituteof Physics, BBSR

Hope this answer helps!