What are virtual particles in space?something imaginary?

Answer 1

The Heisenberg Uncertainty Principle says that you can't know both the position and momentum of a particle accurately at the same time. You can pinpoint the absolute location of a particle but the range of its momentum expands tremendously and vice versa.

Another formulation of the Prinicple says a similar relationship occurs between the energy of the particle and the time it exists. Qunatum theory has taken this to mean that you can have pairs of particles (matter and anti-matter) forming for exceedingly brief periods of time before they annihilate each other. The energy balance comes out to zero and the amount of time these particles exist is so small that they are "virtually" there before they disappear.

They are not specifically imaginary although they can't necessarily be observed. However, the concept of virtual particles is a keystone to Hawking radiation emitted by a black hole. It is possible for a virtual pair to form just outside of an event horizon and one partner falls into the black hole but the other gains enough kinetic energy to escape. This has the effect of the black hole apparently emitting particulate radiation.