Free Astronomy Magazine May-June 2022

31 MAY-JUNE 2022 ASTRO PUBLISHING of this system. “The scenarios we were looking for were rather clear, very different and easily distinguish- able with the right instrument,” says Rivinius. “We agreed that there were two sources of light in the sys- tem, so the question was whether they orbit each other closely, as in the stripped-star scenario, or are far apart from each other, as in the black hole scenario.” To distinguish between the two proposals, the astronomers used both the VLTI’s GRAVITY instrument and the Multi Unit Spectroscopic Explorer (MUSE) instrument on ESO’s VLT. “MUSE confirmed that there was no bright companion in a wider orbit, N ew research using data from ESO’s Very Large Telescope and Very Large Telescope Interferometer has revealed that HR 6819, previ- ously believed to be a triple system with a black hole, is in fact a system of two stars with no black hole. [ESO/L. Calçada] phase is extremely difficult as it is so short,” adds Frost. “This makes our findings for HR 6819 very exciting, as it presents a perfect candidate to study how this vampirism affects the evolution of massive stars, and in turn the formation of their asso- ciated phenomena including gravi- tational waves and violent supernova explosions.” The newly formed Leuven-ESO joint team now plans to monitor HR 6819 more closely using the VLTI’s GRAV- ITY instrument. The researchers will conduct a joint study of the system over time, to better understand its evolution, constrain its properties, and use that knowledge to learn more about other binary systems. As for the search for black holes, the team remains optimistic. “Stellar- mass black holes remain very elusive owing to their nature,” says Riv- inius. “But order-of-magnitude esti- mates suggest there are tens to hundreds of millions of black holes in the Milky Way alone,” Baade adds. It is just a matter of time until astronomers discover them. while GRAVITY’s high spatial resolu- tion was able to resolve two bright sources separated by only one-third of the distance between the Earth and the Sun,” says Frost. “These data proved to be the final piece of the puzzle, and allowed us to con- clude that HR 6819 is a binary sys- tem with no black hole.” “Our best interpretation so far is that we caught this binary system in a moment shortly after one of the stars had sucked the atmosphere off its companion star. This is a com- mon phenomenon in close binary systems, sometimes referred to as ‘stellar vampirism’ in the press,” ex- plains Bodensteiner, now a fellow at ESO in Germany and an author on the new study. “While the donor star was stripped of some of its ma- terial, the recipient star began to spin more rapidly.” “Catching such a post-interaction !