New observations from ESO’s Very Large Telescope have revealed that a binary star system called VFTS 352 is among the most extreme and strangest yet found.
This artist’s impression shows VFTS 352 – the hottest and most massive double star system to date where the two components are in contact and sharing material. Image credit: ESO / L. Calçada.
VFTS 352 is composed of two O-type stars. Such stars are typically between 15 and 80 times more massive than the Sun and can be up to a million times brighter. They are so hot that they shine with a brilliant blue-white light and have surface temperatures over 54,000 degrees Fahrenheit (30,000 degrees Celsius).
According to astronomers, the two stars in VFTS 352 orbit each other in about 24 hours. Their centers are separated by just 7.5 million miles (12 million km). In fact, the stars are so close that their surfaces overlap and a bridge has formed between them.
This system lies about 160,000 light-years away in the Large Magellanic Cloud.
It is not only the most massive known in a class of overcontact binaries – it has a combined mass of 57 solar masses – but it also contains the hottest components – with surface temperatures above 72,000 degrees Fahrenheit (40,000 degrees Celsius).
Such binaries play a key role in the evolution of galaxies and are thought to be the main producers of elements such as oxygen.
They are also linked to exotic behavior such as that shown by ‘vampire stars,’ where a smaller companion star sucks matter from the surface of its larger neighbor.
In the case of VFTS 352, however, both stars in the system are of almost identical size.
This image shows the location of VFTS 352. This view of the Tarantula star-forming region includes visible-light images from the Wide Field Imager at the MPG/ESO 2.2-m telescope at La Silla and infrared images from the 4.1-m infrared VISTA telescope at Paranal. Image credit: ESO / M.-R. Cioni / VISTA Magellanic Cloud survey / Cambridge Astronomical Survey Unit.
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% of their material.
“The VFTS 352 is the best case yet found for a hot and massive double star that may show this kind of internal mixing,” said Dr Leonardo Almeida of the University of São Paulo, Brazil.
According to Dr Almeida and his colleagues, VFTS 352 could be heading for a dramatic end, either with the formation of a single giant star or as a future binary black hole.
“The future of VFTS 352 is uncertain. If the two stars merge, a very rapidly rotating star will be produced,” they wrote in a paper in the Astrophysical Journal (arXiv.org preprint).
“Instead, if the stars continue to evolve homogeneously and keep shrinking within their Roche Lobes, coalescence can be avoided. In this case, tides may counteract the spin down by winds such that the VFTS 352 components may, at the end of their life, fulfill the requirements for long gamma-ray burst progenitors in the collapsar scenario.”
_____
L.A. Almeida et al. 2015. Discovery of the massive overcontact binary VFTS 352: Evidence for enhanced internal mixing. ApJ 812, 102; doi: 10.1088/0004-637X/812/2/102
