  We explain the early excess emission of the Type Ia supernova 2018oh by an
interaction of the supernova ejecta with disk-originated matter (DOM). Such DOM
can form in the merger process of two white dwarfs (WDs) in the double
degenerate scenario of Type Ia supernovae (SNe Ia). We find that an ejecta-DOM
interaction can fit the early light curve of SN 2018oh better than an
ejecta-companion interaction in the single degenerate scenario. By composing
the DOM from two components that were ejected in the merger process with two
different velocities, we show that the ejecta-DOM interaction can account for
the linear rise in the light curve, while the ejecta-companion interaction
predicts too steep a rise. In addition, the ejecta-DOM interaction does not
predict the presence of hydrogen and helium lines in nebular spectra, and hence
does not suffer from this major drawback of the ejecta-companion model. We
consider the ejecta-DOM interaction to be the most likely explanation for the
early excess emission in SN 2018oh. By that we show that the double degenerate
scenario can account for early excess emission in SNe Ia.
