To say Hollywood star Cillian Murphy has had a varied film career would be a bit of an understatement.

In the last couple of years he's played a transvestite in Breakfast on Pluto, an Irish freedom fighter in The Wind That Shakes the Barley, and a psychotic super villain in Batman Begins.

And now the 30-year-old Irish actor, who lives in Hampstead, is boldly going where he's never been before: space, in director Danny Boyle's sci-fi thriller Sunshine.

"I've never been in a science fiction film and I've never played a character like this, so it was all a challenge," says Murphy.

And although he says enjoys the genre, he's clearly no sci-fi geek.

"I was never obsessively into it. I watched Star Wars and Battlestar Galactica but I didn't want to be an astronaut or anything like that.

"For me, film choices depend on the script, not the genre. In Sunshine there was a huge amount for me to work with."

Set in the year 2057, Murphy plays physicist Capa, part of the eight-strong crew of the spacecraft Icarus II, which has been sent on a mission to reignite the sun which is slowly dying.

But with mankind on the brink of extinction, the crew stumble across a distress beacon from the Icarus I, which disappeared on the same mission seven years earlier, and it's not long before Capa and co themselves fighting not only for their lives but for the future of us all.

The film is meant as exciting, big budget rollercoaster ride but Murphy adds that there's more to the movie than meets the eye.

"Yes, it's a science fiction thriller," says Murphy "But also, if you are willing to look a little closer, I think it asks a few questions about science and religion and all that stuff. It's not forcing it down your throat but it's gently nudging you."

He adds: "It certainly makes you a little bit more aware of the fragility of the planet. I have a very loose grasp of physics—or had prior to this movie—and I think you recognise that we have a responsibility. I have a kid and I recognise that his future is in our hands right now."

Despite the out-of-this-world storyline, the film actually came together in a student flat in East London as the cast spent two weeks living together to help break down barriers and create the kind of camaraderie that would exist between a group of astronauts who have been stuck together for 16 months.

While Murphy says it was a fun time—"I wasn't doing much cooking. I was doing more of the boozing," he admits—his wife, Yvonne, was actually pregnant at the time.

"It was tricky," he jokes. "it was like 'see you in two weeks honey!' I'm sure she was delighted. But it was great for the movie. I think the opening scene, when they are all in together having dinner, works because we know each other so well. There's that ease in the way we interact and also a bit of irritation and all that sort of stuff."

But if it took a while to get friendly with the cast, Murphy needed no introduction to Boyle, having already worked with the director on hit post-apocalyptic horror film 28 Days Later…

"Collaborating again is helpful for the actor and the director because there is a shorthand and a trust and it cuts through a lot of the nonsense."

And he adds: "28 Days Later… [was] a very special film for me. It was my first time working with a really established director and it was the first time that a film I made got seen by anybody and made a lot of money.

"And I learnt a huge amount from Danny. He seems to have an endless passion for movie-making which completely infectious. And he knows everybody's name on set. I know that sounds like a small thing but with a crew of 300 people, how do you do that?"

Despite climbing the ladder of success in Hollywood and pondering the mysteries of the universe, Murphy admits it all comes a distant second to becoming a dad.

Now the proud parent of 16-month-old Malachy, Murphy says: "It puts everything in perspective and makes your purpose clearer—to protect and provide for your family. All of a sudden the nonsense that surrounds acting becomes very insignificant.