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There is a strong relationship between a main-sequence star's mass and it's luminosity; as mass of the star gets larger, the luminosity increases very rapidly. This corresponds to higher surface temperatures and correspondingly greater energy production in the star's fusion core, which means the bigger the star, the faster it "burns" its nuclear fuel supply; hence larger stars have shorter life-spans.
Conversely, a main-sequence star of mass comparable to the sun consumes its nuclear fuel slowly enough that it has a typical life-span of about 1010 years. The star described in the article reportedly has a mass of about 0.8 solar masses, and thus its life expentancy is somewhat longer than that that of our sun, probably on the order of about 1.5 x 1010 years. This, BTW, illustrates why we have no examples of Red Giant stars of mass less than 0.8 solar masses; their life expectancy is longer than the current age of the universe, hence, they haven't had enough time to reach the Red Giant stage ("old age") of stellar evolution.
The low luminosity of stars such as this one also explains why it is very difficult to find them; they don't have a very high intrinsic brightness, so unless they are relatively close, they are hard to see.