The longest-living stars are red dwarfs, which are the smallest and coolest type of main-sequence star. Their starting mass is typically between 0.08 and 0.5 solar masses.

Here's why:

* Nuclear Fusion: Stars generate energy through nuclear fusion in their core. Red dwarfs fuse hydrogen into helium at a very slow rate.

* Fuel Economy: Their low mass means they have a small amount of fuel, but they burn it extremely slowly, making them incredibly long-lived.

* Lifetime: Red dwarfs can live for trillions of years, far longer than the estimated 10 billion year lifespan of our Sun.

Important Note: While the starting mass of red dwarfs determines their longevity, the precise lifetime can vary depending on other factors like their chemical composition.