Secrets of the vampire star

VLT telescopes offer clearer picture of transfer of matter from one star in a double system to another

VLT telescopes offer clearer picture of transfer of matter
VLT telescopes offer clearer picture of transfer of matter

These super-sharp images of the unusual vampire double star system SS Leporis were created from observations made with the VLT Interferometer at ESO’s Paranal Observatory using the PIONIER instrument. The system consists of a red giant star orbiting a hotter companion. The remarkable image sharpness — 50 times sharper than those from the NASA/ESA Hubble Space Telescope — not only allows the stars to be clearly separated and their orbital motion followed, but also allowed the size of the red giant to be measured more accurately than ever before. The system consists of a red giant star orbiting a hotter companion. Note that the stars have been artificially coloured to match their known temperatures.

The smaller, hotter star in the double star system SS Leporis is leeching material from its larger, cooler red giant companion

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Credit: ESO/PIONIER/IPAG

Scientists have combined the light from four VLT telescopes to create the sharpest image yet of a star that has lost most of its material to a ‘vampire’ companion.
 

By combining the four telescopes, European Southern Observatory scientists were able to create a ‘virtual telescope’ 130 metres across, with 50 times sharper resolution than the Hubble Space Telescope. This was then used to image SS Leporis, a double star system in the constellation of Lepus, the Hare, consisting of two stars that orbit each other at a distance a little greater than the distance from the Earth to the Sun. 

Because the two stars are in such close proximity, the smaller, hotter star has been able to cannibalise half the mass of its larger, cooler companion, by ‘soaking up’ matter it ejects as a stellar wind.

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“We knew that this double star was unusual, and that material was flowing from one star to the other,” says Henri Boffin from ESO, who is co-author of a paper documenting the findings to be published in the journal Astronomy & Astrophysics. “What we found, however, is that the way in which the mass transfer most likely took place is completely different from previous models of the process. The ‘bite’ of the vampire star is very gentle but highly effective.”