Free Astronomy Magazine November-December 2015

13 NOVEMBER-DECEMBER 2015 SPACE CHRONICLES VFTS 352 is not only the most massive known in this tiny class of “overcontact binaries” — it has a combined mass of about 57 times that of the Sun — but it also contains the hottest components — with surface temperatures above 40,000 degrees Celsius. Extreme stars like the two components of VFTS 352, play a key role in the evo- lution of galaxies and are thought to be the main producers of ele- ments such as oxygen. Such double stars are also linked to exotic be- haviours such as that shown by “vampire stars”, where a smaller companion star sucks matter from the surface of its larger neighbour. In the case of VFTS 352, however, both stars in the system are of almost identical size. Material is, therefore, not sucked from one to another, but instead may be shared. The component stars of VFTS 352 are estimated to be sharing about 30 per cent of their material. (The regions around the stars are known as Roche lobes. In an overcontact binary such as VFTS 352 both stars overfill their Roche lobes.) Such a system is very rare because this phase in the life of the stars is short, making it difficult to catch them in the act. Because the stars are so close together, astrono- mers think that strong tidal forces lead to en- hanced mixing of the material in the stel- lar interiors. “The VFTS 352 is the best case yet found for a hot and mas- sive double star that may show this kind of inter- nal mix- ing,” ex- p l a i n s lead au- thor Leo- nardo A. Almeida of the Univer- sity of São Paulo, Brazil. “As such it’s a fascinating and important discov- ery.” Astronomers pre- dict that VFTS 352 will face a cataclysmic fate in one of two ways. The first po- tential outcome is the merging of the two stars, which would likely produce a rapidly rotating, and pos- sibly magnetic, gigantic single star. “If it keeps spinning rapidly it might T his animated artist’s impression shows the massive double star system VFTS 352. [ESO/L. Calçada]