Astronomers during the last American Astronomical Society conference said that a massive white dwarf star within the cycle of a multiple nova is substantially nearer to our own solar system in contrast to at one time thought. Whenever it actually does collapse into a type Ia supernova -- the resulting thermonuclear explosion will adversely affect life on the planet. Significantly.

The star is actually part of a binary starsystem a white dwarf that leaches mass off its sun-like neighbor called T Pyxidis, situated in the southern area of the constellation Pyxis, referred to as "The Compass Box." The system can be described as an recurrent nova since it has been subjected to frequent novas during the last century, suffering somewhat small thermonuclear explosions around 1890, 1902, 1920, 1944 and 1967, or just about every twenty years. 
It is currently been over Four decades since that last nova in 1967, and in the mean time the white dwarf continues to swell, nourishing off its neighbor. If it carries on to swell, it might eventually reach the Chandrasekhar Limitation, a critical mass at which point immediate gravitational collapse will occur causing a thermonuclear blast comparable to 20 billion billion billion megatons of TNT.

Considering that scientist have recently found out that T Pyxidis is only 3,260 light-years away from us, a neighbor by cosmic standards and a lot closer than up until recently thought, that kind of epic explosion wouldn't be good for our stellar neighborhood. The Gamma radiation which would reach Our planet would be equal to 1,000 simultaneous solar flares bombarding planet earth. The resulting creation of nitrous oxides in the upper atmosphere would undoubtedly completely destroy the ozone, at which point it is safe to say the planet would be compleetly uninhabitable.

But the magnificent scale of the cosmos that allows these kinds of massive, cataclysmic events to unravel also bears a gold lining for anybody on Earth. Although in terms of star life a supernova is probably around the cosmic corner, it is believed to take place millions of earth years from today, a full 10 million years by some estimates. The reality is that we're to far away from T Pyxidis to really tell exactly how big it is or how quickly it is accreting mass. But the end of the world will not be coming tomorrow. Or even in a couple of years.

Excellent video interview about T Puxidis on bottom of page.

http://en.wikipedia.org/wiki/T_Pyxidis