Astronomers searching for the closest black hole to Earth will have to look further afield after one candidate — a mere 1,000 light-years away — drew a blank.
Thomas Rivinius and his colleagues at the European Southern Observatory in Chile theorised in 2020 that binary star system HR 6819 in the constellation Telescopium, made up of two young blue giant stars, could contain a hidden black hole.
The system appears as a single object, as the smaller, B-type star is outshone by its larger Be-type twin. But Rivinius observed that the B star appeared to oscillate over a 40-day period and deduced that it could have an unseen satellite of comparable mass in the form of a black hole. The degree of 'wobble' indicated an object around four times the Sun's mass.
But other astrophysicists were skeptical and the group in Chile teamed up with those postulating counter-hypotheses.
They found the two behemoth stars are just a third of an astronomical unit (AU) apart. One AU is the distance between the Earth and the sun, roughly 150 million km or 93 million miles.
That relatively cheek-to-cheek proximity explained their very short mutual orbit of 40 days — less than half of that of Mercury, our solar system's innermost planet which orbits 58 million km from the sun, about the same distance apart as the two stars.
The scientists now believe they have discovered a new kind of binary star system. The so-called Be star is known to have a disc of gas swirling out from its luminous sphere, previously put down simply to its high speed of rotation. But a new theory is that its gravity is dragging material away from its stellar twin.
The team's paper is published in the March edition of the journal Astronomy & Astrophysics.