The events in Abrams' Star Trek all stem from a supernova that destroyed Romulus, killing Nero's family in the process. Tragic but an avoidable disaster if common sense was used. Why was Romulus not evacuated when it was discovered that the Hobus star is about to go nova? Even as a simple precaution it would have probably been a good idea, it's not like the Romulans don't have enough ships to do it.
According to the official prequel comic ''Countdown,'' the Romulans refused to believe that Romulus was in danger and rejected Spock's plan to use Red Matter to create an artificial black hole to absorb the supernova. Could they not check to see if the Hobus star was really a threat? We can examine light from a star now and work out if it is reaching the end of its life, so you would expect the Romulans to be able to perform a simple scan to evaluate the danger. Instead it is left to Nero, Spock and the Enterprise to make the Red Matter and try to save Romulus. Like I said, this was all in the prequel comic that gave the origin story of why Nero was so angry and obsessed with Spock. Unfortunately the story is by Roberto Orci & Alex Kurtzman who also wrote the movie so that is why none of the science or plot in general makes much sense.
Also, the Hobus star is 500 light years away from Romulus so that means it takes light 500 years to travel that distance. We also know that nothing natural can go faster than the speed of light so it would mean that the Romulans have at least 500 years to evacuate the planet. But somehow the supernova managed to break that law of nature and destroy Romulus quite quickly. For a series that has always tried to keep its science believable, this was too much science-nonsense to allow Orci & Kurtzman a free pass. You lose all the audience members who have a basic understanding of science when they have to stop and ask ''how exactly does a supernova threaten a galaxy?'' like Spock said it did, in the same way Kirk had to stop and ask ''What does God need with a starship?''