A few months ago, scientists announced the indirect detection of the nearest black hole to Earth. But another team is now suggesting a different explanation for this stellar puzzle.
HR 6819: History of a Mystery
From the earliest spectra of HR 6819, scientists identified this source as a bright, early-type Be star — a hot star with emission lines, likely due to the accretion of a circumstellar disk of material. As our ability to resolve detail in stellar spectra has advanced, however, a more complicated picture has emerged.
Studies in the 1980s revealed unexpected narrow absorption lines in HR 6819’s spectra, and a 2003 study showed that these lines were moving over time. This indicated that, though we couldn’t optically resolve them, there were two components of HR 6819: a Be star exhibiting no obvious motion, and a B3 III star on a 40-day orbit.
Artist’s impression of HR 6819 as a triple system. Here, an inner binary consists of a star (blue orbit) and a black hole (red orbit). A third star (blue) circles the inner pair on a wider orbit. [ESO/L. Calçada]But what was the B3 III star orbiting? In May 2020, scientists announced an answer to the ...