This fall brought us two movies — A Star Is Born and Bohemian Rhapsody — that explored the ever-alluring world of rock and pop stardom. What they neglected to do, however, is inform us what it all means. Vox Lux is happy to tell us about the cultural significance of pop goddesses — and tell us, and tell us. This second film from writer-director Brady Corbet (The Childhood of a Leader) is subtitled "A Twenty-First Century Portrait," and it's exactly as pretentious as that sounds.

In his eager and sometimes slapdash efforts to collage cultural traumas and triumphs into something meaningful, Corbet recalls the glory days of Richard Kelly (Southland Tales), without the sense of humor. Yet he has created a showcase for Natalie Portman to give one of those performances that's hard to ignore. Playing a pop star who struts around in spike heels with a pronounced outer-borough accent, channeling Lady Gaga with a dash of "Real Housewives," she single-handedly makes Vox Lux memorable, for better or worse.

First, though, you have to get through the film's dour first half, in which we follow Portman's character, Celeste, as a teenager (Raffey Cassidy). After surviving a school shooting (rendered harrowingly on-screen), Celeste goes viral singing an inspirational anthem penned by her sister (Stacy Martin). A manager (Jude Law) smells money and whisks the girls off to prep them for 21st-century stardom.

While the plot screams "allegory," Corbet renders all this in a grim, naturalistic style that suggests a Brechtian mockumentary. It might have worked, if not for the narrator (Willem Dafoe) who periodically jumps in to comment on Celeste's story with some of the most tortured pseudo-literary phrasing ever heard in a movie.

When Corbet pairs 9/11 footage with Dafoe's solemn announcement that Celeste and America lost their innocence at the same time, one wants to believe the movie is mocking this facile framing. But no other perspective emerges. And when Celeste grows up and becomes Portman, in the film's second half, she spews would-be insights about branding and consumerism that sound much like the narrator's.

The movie doesn't show us how Celeste turns from a shy, pliant, hardworking ingénue into a raucous, angry, substance-addled adult diva. Yet that transformation is perhaps the movie's most plausible aspect, simply because we've seen similar evolutions in the gossip rags. Herself a former child star, Portman clearly relishes cutting loose, giving adult Celeste the hard edges of Madonna in Madonna: Truth or Dare and the campy panache of Bette Davis in All About Eve. This woman has spent years being America's sweetheart, an emblem of survival and redemption, and now she doesn't give two fucks about anything.

Yet Portman's performance sort of just sits there, a thing unto itself, because the film lacks a dramatic arc. The tension between the two sisters, the unresolved issues of Celeste's past, the specter of a recent terrorist incident whose perpetrators used iconography from one of her videos — all these are threads that lead nowhere. Even the reappearance of Cassidy, now playing Celeste's teen daughter, doesn't add much beyond an audience for Celeste's lectures. The film culminates in a performance sequence (with songs by Sia) that should be cathartic but is mainly just flashy.

The symbiosis of celebrity and tragedy — and how both attract unscrupulous entrepreneurs eager to cash in — is a timely subject. But pushing cultural hot buttons isn't the same as making a great movie about the culture, and Vox Lux ultimately feels as opportunistic and empty as Celeste's career.