Astronomers who thought they had discovered a black hole on our cosmic doorstep have said they were mistaken, instead revealing they have found a two-star system involving a stellar “vampire”.
The system, known as HR 6819 in the constellation Telescopium, was in the headlines in 2020 when researchers announced it contained a black hole. At just 1,000 light years from Earth, it was the closest yet found to our planet.
At the time the team behind the work said the presence of a black hole was necessary to make sense of the movement of two stars in the system, suggesting a black hole and one star orbited each other while the second star moved in a wider orbit.
Now the researchers say they were mistaken: the black hole does not exist.
Dietrich Baade, an emeritus astronomer at European Southern Observatory (ESO) and a co-author of the work, said just one blob of light was previously detected, containing the hallmarks of two stars.
Since both stars are of similar brightness and the same age, they would normally have the same mass and would whirl each other around with similar, high velocity.
“Since we saw that only one of the stars was whirled around at high velocity by some massive object, which we didn’t see, we assumed this unseen massive object to be a third body, namely a black hole,” he said.
But other researchers disputed the idea, suggesting the system contained two stars alone, one of which had recently been stripped of mass by the second, sometimes called a stellar “vampire”, making the latter far more massive.
Writing in the journal Astronomy & Astrophysics, Baade and colleagues report how the groups teamed up to analyse fresh data from the ESO’s Very Large Telescope (VLT) and Very Large Telescope Interferometer (VTLI).
“Science should be about the open questions that everyone is trying to solve, and not about who was right and who was wrong,” said Dr Julia Bodensteiner, a co-author of the study from the ESO who proposed the “vampire star” explanation.
If a black hole was indeed present, the two stars would be expected to have a large separation. However, in the scenario with no black hole, the stars would be expected to be much closer together.
The results from the VLT revealed no indication of a second star in a wide orbit. In addition the data suggested that both stars contributed to light captured from a single bright source – again suggesting they were sitting close to each other.
The findings were further backed up by data from the VLTI, which in addition revealed that the two stars were orbiting each other.
“Because the stripped star had lost most of its mass, the second star can reel it around quite easily while its effect on the other star is equally easily missed,” said Baade.
While the findings scotch the idea of a black hole, the researchers remain upbeat.
“The stripped star is even more exciting than the black hole because it was caught in a phase that lasts only a very small fraction of the total lifetime of the system,” said Baade.
“The excitement is not about the low chances of the discovery but about the stripped star revealing the inner part of the star. The stripping has removed the thick intransparent curtain of the outer layers so that we can look much closer to where the star has generated the energy that it is radiating away and has synthesised new elements.”
Baade added that when such elements were ejected, the stardust could form not only new stars but also planets and their inhabitants.
