Okay, I know that sun wont become BH (Black Hole) , and I know about Chandrasekhar limit and Tolman-Oppenheimer-Volkoff limit, etc. But my question is different. We know, M = m × √(1-v^2/c^2 ) . where m is rest mass. ( Don't know much latex, sorry ) So now we do know the rest mass of sun, so if it were moving fast its mass should increase, in accordance to equation so, at some velocity (definitely less than c, as at that velocity mass will be ∞) its mass will be that much as is required for black hole formation. Also the physical laws that are required for BH formation such as exclusion principle and chemical interaction etc. should hold good in that reference system too. (As says the Principle of relativity) Does at that point will our sun become BH. And if it does; than for whom, for someone in reference system K' or for someone observing it from system K. Please don't say, that sun can't (or won't) be moving at that speed, or ask me how will I get it to that speed I am not taking about "how and when" I am talking about "what if" case?