Context: In general relativity, a vanishing stress-energy tensor implies, through Einstein field equations, the vanishing of all the components of the Ricci tensor. Vacuum does not mean that the curvature of space-time is necessarily flat: the gravitational field can still produce curvature in a vacuum in the form of tidal forces and gravitational waves (technically, these phenomena are the components of the Weyl tensor). The black hole (with zero electric charge) is an elegant example of a region completely "filled" with vacuum, but still showing a strong curvature.

Question: what is a perfect example of a filled vacuum showing a curvature?
Answer: The black hole

Question: Who's equations  helped to imply vanishing of the Ricci tensor?
Answer: Einstein

Question: what produces curvature in a vacuum?
Answer: tidal forces and gravitational waves

Question: What has no electric charge?
Answer: black hole

Question: What kind of electric charge does a vanishing stress-energy tensor have?
Answer: Unanswerable

Question: What is a black hole a part of?
Answer: Unanswerable

Question: What field around the Earth was discovered by Einstein?
Answer: Unanswerable

Question: Tidal forces and gravitational waves can produce zero what?
Answer: Unanswerable

Question: What is the shape of a gravitational field?
Answer: Unanswerable