The Star Witches (The John Lymington Scifi/Horror Library #10)

Just before the horror, the Reverend David James discovered that a coven of witches was using his church for worshiping Satan and calling up the dead.
Alone in his mansion, scientist Harry Royce was employing electronic devices to reach the outer limits of the Universe.
When the invasion began, it was not known whether the invaders were aliens from a contaminated star or lost souls erupting out of Limbo. Two things became clear: It could not be stopped, and once it was completed, there would be no sane person left on Earth.