Ph.D

After completing your B.Sc in Mathematics, you could pursue a course in M.Sc Astronomy from some of the top colleges in India. This would open up a number of avenues for you in this field. B.Sc. in Mathematics should help you as Mathematics is a major part of astronomy and space research. If needed, you could plan for a PhD in astronomy and become a teacher in this field.

As per thier website, Himalayan University is recognized by the UGC - University Grants Commission under Section - 2(f) of the UGC Act, 1956 and hence empowered to impart higher education at all different levels of Under-Graduate and Post-Graduate. Himalayan University is included in the list of approved universities in India listed by UGC Approved Universities. Therefore, degrees awarded by University is valid for Government and Private sector jobs.

If your talking about distance PhD many universities do provide. IGNOU is one of the examples of universities which provide PhD facility and it's actually one of the best university in India to pursue online studies.

Indira Gandhi National Open University

PhD is done from from University not college. Make a list of universities and find out which ones are the best.

The required minimum qualification for admission to a Ph.D Program shall normally be a two years Masters OR M.Phil Degree from any accredited Indian or Foreign University in the relevant field. She/he must have obtained either a minimum of 50% marks or Equivalent Grade in the M.Phil degree or a minimum of 55% marks or Equivalent Grade in the Masters Degree (for all disciplines except Engineering and Technology), however, overall 60% at all academic levels will be desirable.

The first and basic qualification required for a Ph.D course is that you must have completed your Masters degree course.
To apply for Ph.D. you can either directly apply to the professors of different universities sending them your resume, Statement of purpose
and your research papers. Or you can appear for UGC-NET examination.
And then, sending your NET scores to the professors under whom you want to undergo your Ph.D course.