A Vampire Star acts in the same way a supernatural vampire does in that it 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 be destroyed or turned 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 discovered Vampire Star 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 victim, the larger neighbour. 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.
Blue stars in star clusters stand out from the other stars in the cluster because they look more youthful and younger than the other stars in the cluster. The cause of them looking hotter and bluer than the others is because they suck hydrogen from other stars in the cluster.
Most Blue Stragglers will be in pairs or more, however, scientists have discovered where there are some Blue Stragglers that aren't in a pair. Although the companion star might not be seen, the companions effect on the main star can be noticed. Scientists discovered some solo Blue Stragglers in NCG 188 in Cepheus. The Blue Stragglers might have already consumed the companion star fully and therefore not cooled down yet. Space
Although the terms Cannibal and Vamprie Stars seem to mean the same thing and authors have been known to use Cannibal instead of Vampire. If you want to distinguish them, a Cannibal Star would be one that has consumed its companion star in one go rather than sucking hydrogen from its neighbour. When a star begins its red giant phase, it'll expand and any close by stars will be consumed as a whole rather than in pieces.
Betelgeuse, one of the brightests and most well know stars in the night star is reckoned to be a Cannibal Star. Betelgeuse is believed to have had a companion star that Betelgeuse consumed either as it expanded and ate it or sucked the life out of it. The theory is based on that the star is rotating faster than it should be for its age. It is estimated that the consumption took place about 100,000 years ago, quite recent in astronomical terms. Daily Mail
A lesser known example of a Cannibal Star is that of BP Piscium, a star that is in the constellation of Pisces the fish. The star is an older version of our Sun and is observed to have a disk of gas surrounding it. Its known to be an older star by the chemical composition of the star, it doesn't contain much in the way of Lithium which younger stars are known to have. New Scientist
Its also been seen that the star has jets shooting in different directions. A disk and jets are normally associated with younger stars not something as old as BP Piscium. The current theory is that the star might have cannablised a nearby star or planet and the result is the streams and the disc.
Our Sun in a few billion years so don't worry will probably go the same way as BP Piscium, it will consume the local planets first. Technically speaking not a cannibal but it will consume as a carnivore the planets as there are no inner stars.
A second round of planetary creation might be in the works, long after the deaths of the original planets.Daily Mail