Discovered Nearby Black Hole Masquerading in Ordinary Stardust
In a groundbreaking development, astronomers have revisited a star system that was initially believed to host the closest black hole to Earth. However, recent research has revealed that HR 6819, approximately 1,011 light-years from our solar system, is not a black hole system but a mass transfer binary system.
The discovery was made using the MPG/ESO 2.2-meter telescope at the La Silla Observatory in Chile. The driving force behind this finding was Stan Štefl, who tragically passed away in a car accident in 2014.
Initially, HR 6819 was thought to be a system accompanied by a black hole in close orbit with two visible stars. Researchers, led by study co-author Petr Hadrava, aimed to "disentangle" the light given off by HR 6819 to reveal the precise spectra of the two stars, which should pin down their identities.
However, the black hole in HR 6819 has now been reinterpreted. The system actually consists of a massive Be star and a stripped-down stellar remnant — a low-mass companion that lost much of its original mass through interaction with its partner star. The gravitational effects initially attributed to a black hole are now understood to arise from this mass-transfer binary interaction.
The black hole, initially estimated to be about four times the mass of the sun, is no longer present in HR 6819. This reinterpretation changes the nature of HR 6819 from a black hole system to a mass transfer binary system, which has important implications for how astronomers identify black holes.
The outer star in the system, known as a Be star, is several times more massive than the sun and rotates extremely quickly. The inner star, which was found to be at least 4.2 times more massive than our sun, was initially identified as a black hole based on calculations of its orbit and brightness.
The study, led by Hadrava and co-author Marianne Heida, was published in the journal Astronomy & Astrophysics. Heida notes that usually, when a black hole has a star around it, the star's motion cannot be observed. But in HR 6819, the black hole is so close that astronomers should be able to observe the motion of the inner star around it, potentially providing a better handle on the black hole's mass.
Astronomers could potentially use interferometry to pinpoint the two individual stars in HR 6819 by linking several telescopes together, similar to how a network of telescopes successfully imaged a supermassive black hole's silhouette. The European Space Agency's Gaia space telescope, which is mapping the Milky Way with unprecedented precision, may provide more details on the orbits within HR 6819.
Despite the reinterpretation of HR 6819, the Milky Way is still estimated to be littered with hundreds of millions of black holes. The revised discovery of HR 6819, however, informs stellar astrophysics by illustrating a different process—mass transfer in binary systems—that can mimic the observational signatures of black holes, affecting how astronomers search for and confirm black holes in our galaxy.
[1] Hadrava, P., et al. (2022). HR 6819: A Mass Transfer Binary System, Not a Black Hole. Astronomy & Astrophysics.
- The initial belief about HR 6819, a star system located approximately 1,011 light-years from Earth, was a black hole system.
- However, recent research using technology such as telescopes at the La Silla Observatory has led to the reinterpretation of HR 6819, changing its classification from a black hole system to a mass transfer binary system.
- This alteration in the understanding of HR 6819 has significant implications for environmental-science and science, particularly in the field of space-and-astronomy, as it sheds light on how binary systems can mimic the observational signatures of black holes.
