HOLLYWOOD - Natalie Portman used to dream of making a movie about dance. As a youngster, she'd taken lessons and envisioned herself becoming a prima ballerina one day. So when auteur Darren Aronofsky asked her to star in "Black Swan," his psychological drama set in the world of professional ballet, she leaped at the chance.

Portman plays a young ballerina named Nina who has devoted her life to dance. Her hard work and commitment are rewarded when she lands the lead in a production of "Swan Lake." But as she prepares for the role of a lifetime, the petite dancer is threatened by the rise of a newcomer (played by Mila Kunis), who she believes wants to steal her spot. She is pushed to the breaking point by the company's brilliant but cruel artistic director (Vincent Cassel) and her controlling ex-ballerina mother (Barbara Hershey).

"Black Swan" is a dark look at the little-known world of professional ballet and how the physical demands of the craft can be accompanied by excruciating psychological demands. Aronofsky calls "Black Swan" the companion piece to his Oscar-nominated drama "The Wrestler." Like that 2008 film, "Black Swan" examines the physical and emotional turmoil those individuals endure in their pursuit of their passion.

Portman welcomed the opportunity to explore the physical and emotional side of a tragic but fascinating character.

"Darren had this idea that was not just relating to the dance world but also had this really complicated character - two characters really - to go into. It was just something completely exciting," she said.

Best known for her role as Queen Amidala in George Lucas' "Star Wars" prequels, the Israeli-born actress admits it was tougher than she expected to get into prima ballerina form at age 28. (She's now 29.) Most professional ballerinas have more than a decade of training and professional experience under their tutus by that age.

"Even if you've taken dance lessons before, you just don't realize how much goes into it at the elite level," said the veteran actress.

Portman, who is preternaturally graceful and slim, committed herself to an intensive regimen that included dancing, swimming, weight training and cross training. She practiced five hours a day, every day, for 10 months before production, which took place in several New York locations. She worked with some of the best ballet trainers in the business, including the legendary Georgina Parkinson, a one-time principal dancer with the Royal Ballet and mistress of the American Ballet Theatre for 30 years. Parkinson died just two weeks before the film went into production, which shocked and saddened the cast and crew.

"She was an amazing coach," Portman recalled.

Portman had a workout partner in Kunis ("That '70s Show"), who plays Lily, her rival. Both actresses sustained injuries while preparing for their roles. Kunis tore two ligaments and dislocated her shoulder. Portman injured a rib.

"It was pretty intense, because I had to deal with it for about half the shoot," Portman recalled.

But Portman forged ahead with her training under the tutelage of choreographer Benjamin Millepied, a principal dancer with the New York City Ballet. The hard work paid off. Her dancing to the classic Tchaikovsky composition looks effortless on-screen.

The physical discipline Portman acquired preparing for her role helped her develop the emotional side of the character, she said. "You get the sense of this sort of monastic lifestyle of only working out," she said. "It is a ballet dancer's life, where you don't drink, you don't go out with your friends, you don't have much food, you are constantly putting your body through extreme pain - and you get that sort of understanding of the self-flagellation of a ballet dancer."

Like her character, Portman said, she was willing to do anything for her director, even if it meant driving herself to the point of pain and fatigue. Unlike Nina, though, she could drop out of character as soon as she finished shooting a scene.

"I'm not someone who lives to stay in character," she revealed. "This clearly had a kind of discipline that lends itself to me being probably more like my character while we were shooting than past experiences. But I just go back to my regular life afterwards."

Having majored in psychology at Harvard, Portman objectively psychoanalyzed her character, whose nervous tics include scratching her back to the point of bleeding and picking at her nails constantly.

"This was actually a case where something I learned in school translated into something practical in real life," she said with a smile. "Nina's was absolutely a case of obsessive compulsive disorder, and ballet really lends itself to that because there's such a sense of ritual."

Portman doesn't consider herself a perfectionist, though she strives to incorporate discipline and focus in her acting. She's been at it since 1994, when she starred in Luc Besson's emotional drama about a hit man who befriends a young girl in "The Professional."

She has since appeared in 25 films, including "Beautiful Girls," "Cold Mountain," "The Other Boleyn Girl," and most recently, "Brothers." She earned an Oscar nomination for her performance in Mike Nichols' 2005 drama "Closer."

She will show off her lighter side in 2011, starting with the Ivan Reitman comedy "No Strings Attached," co-starring Ashton Kutcher. She also appears in "Thor," as the comic book hero's love interest, Jane Foster. She currently is in production on "Your Highness," a comedy set in medieval times.

The strict diet regimen she endured while filming "Black Swan," is now off the menu.

"The first meal I believe I had after we finished the film was pasta for breakfast, lunch and dinner, and like, all the time," she said with a giggle.