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Asuuming the vacuum has zero mass (negligible ZPE of the vacuum) and since Black holes generate gravity without the presence of mass (i.e. singularity at the center of a Black Hole) does this mean that the vacuum is gravitational?

If yes, because free space vacuum is isotropic and homogeneous we would not feel its gravity effect and only feel it at the locations where there is a vacuum density gradient like in planets, stars and Black holes. I assume, that in the presence of normal matter the vacuum density changes locally.

In that sense does gravity originate and sources out of the vacuum?

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Already in special relativity, mass and energy are equivalent (the famous formula $E=mc^2$). So it's not surprising that in special relativity, it's not just mass that creates a gravitational field, but also energy (or even more generally, stress-energy).

So if you have a vaccuum with energy - e.g., a lot of photons - it creates a gravitational field.

Even more interesting thing happens in black holes, which have no particles whatsoever but a "self sustaining" gravitational field. It's sort of circular reasoning: Because near a black hole spacetime is bent, it causes a gravitation field and stress-energy, and this stress-energy in turn causes space-time to bend! The black hole, Schwarzschild's solution, is a particular solution of Einstein's field equations where the bending of space is exactly enough to create energy which creates the same bending.

Another thing worth noting is that Einstein's field equations ("General Relativity") also allows the concept of a cosmological constant, a.k.a. vacuum energy. It is possible that vaccuum itself has energy which in turn bends space and creates gravitation. We currently believe that our universe indeed has a small amount of that so-called "Dark Energy", and it is causing our universe's expansion to accelerate.

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    $\begingroup$ Because near a black hole spacetime is bent, it causes a gravitation field and stress-energy, and this stress-energy in turn causes space-time to bend. No. $T^{\mu\nu}$ for a Schwarzschild black hole is zero. There is no stress-energy. $\endgroup$
    – Ghoster
    Feb 15 at 4:55
  • $\begingroup$ Right, Sorry about that, I messed up my attempt at an answer. physics.stackexchange.com/questions/648643/… has a better discussion of how Schwartzshild's solution is possible even though the stress-energy is zero everywhere. This is still an answer for the original question - it's another example of the possibility of graviation even without matter or even stress-energy. $\endgroup$ Feb 15 at 7:42

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