When Mica Levi composed her debut film score at age 26 for the movie “Under the Skin,” starring Scarlett Johansson as an alien, people took note. Among the many who detected an important new discovery was Chilean director Pablo Larrain, who was on the jury when the film screened at the Venice Film Festival in 2013.

“I didn't know anything about her,” Larrain said by phone from Chile. “But at that moment, I just thought that it was really something that I had never heard before — and nowadays that's something very, very, very hard.”

Levi was the director's first choice when he made “Jackie,” which recounts the traumatic days of Jacqueline Kennedy after her husband's assassination. “Not just because of her work,” he said, “but also because a feminine sensibility would be interesting to bring to the project.”

Known by her stage name Micachu and for her band's experimental pop music, Levi wrote a score as unorthodox as her process. Having only read the script and seen isolated scenes (Larrain was still editing the film), she wrote disparate parts piecemeal, often with the simple motivation of making music that Jackie “would be into, that was sort of her vibe.”

“The bits that stuck out to me the most, I guess, were with the journalist where she's a bit sassy,” Levi explained by phone from London. “And the time and the way she presented herself — I just hazarded a guess.”

An unsteady waltz with a meandering flute line and shivering strings plays to Jackie's disorientation in Dallas and later when she breaks the news to her children. A birdlike flute flits over a repeating cycle of string chords, heartbroken but hopeful, as Jackie processes grief with her friend Nancy.

Levi wrote music to convey the first lady's traumatized internal state and the violence of the assassination: quivering tremolo strings, queasy glissandos and an emotionally knotty adagio for the finale. But the score complicates emotions in each scene, offering abstraction and discomfort. This effect was furthered by Larrain's decision to place pieces Levi wrote against scenes different from the ones they were written for. The opening piece, for instance — a series of melting chords that wrests audience attention with their prominent accompaniment to a black screen — was conceived for a later sequence.

“Sometimes people will support a specific idea or emotion with the music, and it will just be the same as what we're looking at,” Larrain said. “Mica would do something totally different, and then with the image it would create a third idea, which is what creates this sensation of ambiguity — sometimes sorrow, sometimes painful, sometimes extremely enlightening and bright, and sometimes very dark. It just elevated the film into something so beautiful.”

The score was recorded by the London ensemble Orchestrate, and its pared-down ensemble included a small string section and woodwinds, as well as bagpipe and snare drum for the officialism of the proceedings.

Larrain decided to tell the story of “Jackie” through Natalie Portman's eyes. “It's like a cosmic door to something that you won't be able to describe, it's something that the audience will complete,” he said. “And then you have Mica's score that will take you to a place that you just keep wondering: Where are we? What's going on? Every single one of us will feel something — it might be similar to each other, but it's also very distinctive, because it becomes very personal.”