if gravitons are subatomic particles how can it escape from black hole because nothing escapes from it. and create a gravitational field around it
This is a very reasonable consideration from mazhar ali. Gravitons are believed, by some Standard Model freaks, to be elementary particles (EPs) which mediate gravity, and apparently at infinite distance since gravitational fields (GFs) are essentially infinite, but field strengths drop as the square of the distance, like most radiation. These GFs also propagate at the speed of light, like all electromagnetic radiation. If gravitons exist, they would have to have some similar characteristics to photons at the very least, one would think. And photons surely exist without doubt, and are themselves EPs.
So gravitons would have to "escape" from a black hole? This assumes that they are formed within or at the surface of an object with mass. There are examples where this seems to be contradicted. Light cannot escape from a black hole, or so we are told. But light also has no mass, so how can it be trapped in a black hole? I suspect the mass-energy equivalence of light may have something to do with this.
So suggesting that gravitons establish a GF around a black hole would put very serious constraints on the their nature. That should not be a serious problem since there are so many things out there that do happen regardless of constraints. Neutrinos are almost unimaginable, but most Standard Modelers accept them. Indeed, it seems their existence is without a doubt.
Since no one has a clue as to how mass generates GFs, the graviton must still be in the running. Look at all the other unique things that EPs give us. All of the quarks, gluons, electrons, photons, neutrinos, etc., and the most recent, the Higgs Boson. That one took the LHC to find. Perhaps with enough effort, and maybe a bigger collider, something will come out to provide evidence for the graviton. It would seem like everything can be boiled down to EPs. For those like me who know very little about gravitons, I will give them a 50:50 chance of existing, and a much lower chance of ever being detected.
If they do exist, it would seem they would have a very tenuous nature, to say the least.....