I have seen a documentary on TV and it said that there is space without matter. Matter can not be created nor destroyed and the space exists because matter exists. Another fallacy that is usually said is the expression “concentrated high density matter”. Wrong! Substance may be more or less concentrated, more or less denser. Where is more substance, there is less physical field and vice versa. Physical field is generated by the substance.
Gravitational field is generated by the mass of bodies. As mass is greater, the greater the gravitational field is. Mass, which measured in kilograms is a measure of inertia, invariant in inertial reference and should not be confused with the amount of substance which is measured in moles, which is invariant in both inertial and non-inertial references.
The same body can generate higher or lower gravity depending on its own referential, if at some point is inertial and at another point is non-inertial. It is inertial when it is at rest state or when it moves straight and uniform and non-inertial is when moving curvilinear (uniform or variant) or straight variant (accelerated or slowed).
But all these moves are relative, depending on the observer’s position. A body moves and at the same time an observer sees it in rest state, another sees it moving rectilinear etc. Everything is relative and it depends on the referential in which the observer is. I see it white, you see it black. But it is the same sheep, because there is no other one! That’s relativity theory that most people do not understand, or worse, they misunderstanding it.
About mass we can talk a lot. It is closely related to the weight of bodies. As the mass is greater, the greater the weight and therefore it is directly proportional.
Ions generate electric field, magnets or electric current generates a magnetic field, positrons generate positron field, mesons generate meson field etc. So, the virtual is generated by the real and physical field is generated by the substance.
But no substance can exist without physical field. Electrons, even if they would exist freely somewhere in space, they do have electrical field around them and repel. Atoms have electric field inside them and so can continue until tomorrow. I have to mention something about the real and virtual: everything is virtual have something real behind that generates it but not all is real generates something virtual.
The rest mass or inertial mass is directly proportional to the amount of substance. This is valid only in inertial references. All inertial references move rectilinear and uniform to each other. The Moon has a gravity 6 times smaller than the Earth because the Moon has a mass 6 times smaller than the mass of the Earth, but both mass of the Earth and mass of the Moon are not inertial because both celestial bodies have a circular path and automatically have centripetal acceleration. Centripetal acceleration vector changes direction all the time, just the size of the module is the same.
Direction of tangential acceleration vector is always tangent to the path, as their name suggests. Centripetal acceleration is also called normal acceleration. Centripetal acceleration and tangential acceleration are the two components of decomposed acceleration by the parallelogram rule or triangle rule.
So the conclusion is that the size of the mass of the two celestial bodies depends on both the amount of substance, density and linear and angular velocities of their bodies.