This looks like just an arbitrary chunk from the middle of some calculations. As such it is pretty meaningless. There is no definition of what the various terms, like r and DM, are meant to represent. It doesn't help either that you have posted it sideways. Since the word "light" appears, and E=mc², it looks as if it may have something to do with relativity. Perhaps DM stands for dark matter or something, which would probably make it about cosmology. But without more information all we can do is guess.
If you want comment, you need to post it from the start of the calculation, the right way round so we can read it easily, with an explanation of what it is about, and with the algebraic symbols defined.