Many celestial objects with peculiar properties not expected of single stars at any point of their lifetimes exist within our universe. Of these, some of the most notable are listed below: millisecond pulsars, objects which emit a periodic radio pulse with a period of a few milliseconds; X-ray binaries, which are massive compact objects which are accreting material, and in the process of which become very bright X-ray sources; novae, which are stars that suddenly become much brighter and then fade away in a very short period of time, giving the impression that a star apparently just appeared out of nowhere and immediately disappeared afterwards; hot subdwarfs, stars which lose their outer envelope, exposing their hot cores, and hence appear as a very hot star that is small in size, and is responsible for a disproportionate amount of UV radiation in their neighborhoods; and last but not least, blue stragglers, also known to some as “vampire stars”, are old stars which “rejuvenate” themselves by obtaining mass from a companion.

In all of these cases, the existence of these objects can be explained by binary evolution, which can be simulated using our binary evolution codes. Conversely, they provide opportunities for testing our binary population synthesis codes and theories.