It acts in the same way a supernatural vampire will suck blood from its victim except its hydrogen and not blood. Eventually the Vampire star will suck too much out of the victim that the victim will turn it in a white dwarf star. It could also possibly explode in a supernova destroying both stars in the process. The Vampire star will start off as the smaller star but nearing the end of the sucking process will inevitably be the larger one. The sucking star, normally a blue star is also known as a blue straggler, as it sucks, it gives the appearance of being a younger star when its not. The white dwarf star can gain revenge later by sucking back hydrogen from the vampire star.
The most recently Vampire Star discovered as of 2010 is that of 17 Leporis, a binary star system in the constellation of the Hare, Lepus. In the released picture by E.S.O. it shows two stars, a giant red star and a smaller blue star. The blue star although smaller is the hotter of the two stars and is the Vampire star sucking hydrogen from its larger neighbour. The blue star is the hotter of the two stars. The colours in the picture have been enhanced for viewing. Though you don't see a stream from one star to the other, it probably uses a different method.
Despite the looks, the blue star is more massive than the red star at 2.7 times the Sun compared to 1.3 times of the red. Even though the blue star is the smaller, it has more mass than the larger star. This case of vampirism has been in existence for about 500,000 years and will continue for another 200,000 years. The red star will die first as a white dwarf with the blue star following much later. Ref: Wired
According to the European Southern Observatory (E.S.O.), the majority (70%) of massive stars could have a close relationship with a smaller star. As a result of this discovery, the theory of star formation may well need to be revised. Ref: Space
When you look at a star cluster, you can generally work out how old the cluster is by the colour of the stars. Blue stars are young stars, yellow stars are medium and red stars are old stars. The stars in the cluster are generally all the same age but there can be blue stragglers inside the cluster which is evidence of Vampire stars having feasted on other stars.