For Astrophysics you must have Physics and Mathematics compulsorily in your course work.
IIT JAM MSc Physics criteria is that you must have 55% marks in your graduation and must have Physics and Mathematics (Atleast in two semester) then you are eligible. You can take Astrophysics as your specialization in your MSc.
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The minimum eligibility criteria for studying MSc in Astrophysics is
The candidate must have passed higher secondary or equivalent course from a recognized examination board with science stream.
The candidate must have an aggregate of 50% in a bachelor's degree of science
Many colleges conduct their own exam. If you want to study in Central universities you can appear for CUCET exam, If you wish to study in IITs and IISC you can give JAM exam.
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