Can a white dwarf star be restarted if there was a collision with another white dwarf?

Yes, a white dwarf star can potentially be "restarted" if it collides with another white dwarf under certain conditions. If the merger results in sufficient mass and the combined core temperature reaches the necessary threshold for nuclear fusion, it could trigger a new round of fusion reactions. This process may lead to a type Ia supernova if the mass exceeds the Chandrasekhar limit, or it might form a more massive white dwarf or another type of star, depending on the specifics of the collision.