Single X-ray StarsMain article: Single X-ray star
In addition to the Sun there are many unary stars or star systems throughout the galaxy that emit X-rays. β Hydri (G2 IV) is a normal single, post main-sequence subgiant star, Teff = 5800 K. It exhibits coronal X-ray fluxes.
The benefit of studying single stars is that it allows measurements free of any effects of a companion or being a part of a multiple star system. Theories or models can be more readily tested. See, e.g., Betelgeuse, Red giants, and Vega and Altair.
Read more about this topic: X-ray Astronomy