Natalie Portman, Justin Beiber: A day out in Hollywood

Here's what your favourite Hollywood celebrities have been up to.

Actress Natalie Portman arrives for the world premiere of Thor: The Dark World at Leicester Square in London on October 22.

The second film in the superhero series, Thor is set for a November release in India and the US.

Thor leading man Chris Hemsworth, who won worldwide critical acclaim with his portrayal of late British Formula One racer James Hunt in last film Rush, poses at the premiere.

Actor Tom Hiddleston -- Thor: The Dark World's Loki -- photographed at the red carpet premiere.

Actress Kat Dennings arrives for the world premiere of Thor : The Dark World.

The star of television show Two Broke Girls, Dennings plays Darcy Lewis in the film.

The Wire actor and Thor cast member Idris Elba arrives.

Elba plays Heimdall in the film.

Singer Katy Perry performs Roar during the release party of her album Prism at the iHeartRadio Theater Los Angeles in Burbank, California on October 22.

Canadian pop singer Justin Bieber performs during his Believe concert at the Olimpic Stadium in Santo Domingo, Dominican Republic, on October 22.