Who won an Oscar for her portrayal of a young dancer in the 2010 movie "Black Swan"?

"Black Swan" is a 2010 American psychological horror-thriller film directed by Darren Aronofsky, written by Mark Heyman, Andres Heinz, and John McLaughlin, and starring Natalie Portman, Vincent Cassel, Mila Kunis and Winona Ryder. The plot revolves around a production of Tchaikovsky's Swan Lake ballet by a prestigious New York City company. The production requires a ballerina to play the innocent and fragile White Swan, for which the committed dancer Nina (Portman) is a perfect fit, as well as the dark and sensual Black Swan, which are qualities better embodied by the new arrival Lily (Kunis). Nina is overwhelmed by a feeling of immense pressure when she finds herself competing for the part, causing her to lose her tenuous grip on reality and descend into a living nightmare.

The film received five Academy Award nominations and Portman won Best Actress for the film, as well as many other Best Actress awards in several guilds and festivals. Aronofsky was nominated for Best Director and the film was nominated for Best Picture. It is the fifth horror film to be nominated in the Best Picture category, following "The Exorcist" in 1973, "Jaws" in 1975, "The Silence of the Lambs" in 1991, and "The Sixth Sense" in 1999.