Astronomy

Dear Dhrujay,
Astrophysics is the branch of astronomy that employs the principles of physics and chemistry to ascertain the nature of the heavenly bodies, rather than their positions or motions in space. Among the objects studied are the Sun, other stars, galaxies, extra-solar planets, the interstellar medium and the cosmic microwave background. Their emissions are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. Because astrophysics is a very broad subject, astrophysicists typically apply many disciplines of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.

They offer an integrated M.Tech + Ph.D program. As mentioned on their website here is the eligibility
'The Integrated M.Tech- Ph.D (Tech.) Programme will admit bright, highly motivated students with a three years B.Tech. degree (Post BSc Hons) in Optics and Optoelectronics / Radio Physics and Electronics from CU or B.Tech / BE degree in Electrical/ Instrumentation/ Electronics and Communications /Computer Science and Engineering from an institution recognized by AICTE. A candidate with M.Sc degree in Physics / Electronic Science / Applied Mathematics /Applied Physics from a UGC recognized institution is also eligible to apply'.
Hence you must hold either of these degrees and pass out with flying colors to be eligible. They will also hold an entrance test. Please check the website of IIAP.