The black hole closest to us is not a black hole at all

The black hole closest to us is not a black hole at all

In 2020, a team led by astronomers from the European Southern Observatory (ESO) reported the closest black hole to Earth, located just 1,000 light-years away in the HR 6819 system. But the results of their study have been disputed by other researchers. , including an international team based in KU Leuven, Belgium. In a recent article, these two teams teamed up to report that no black hole actually exists in HR 6819, which is instead a two-star "vampire" system in a rare and short-lived phase of its evolution. >
The original HR 6819 study received significant attention from both the press and scientists. Thomas Rivinius, an ESO Chilean astronomer and lead author of that article, was not surprised by the astronomical community’s welcome to the discovery of the black hole. Rivinius and his colleagues were convinced that the best explanation for the data they had obtained with the MPG / ESO 2.2-meter telescope was that HR 6819 should be a triple system, with one star orbiting a black hole each. 40 days and a second star in a much larger orbit.

But a study by Julia Bodensteiner, then a PhD student at KU Leuven, Belgium, proposed a different explanation for the same data: HR 6819 it could also be a system with only two stars on a 40-day orbit and no black hole. This alternative scenario would require one of the stars to be "stripped", which means that, at an earlier time, it had lost a large fraction of its mass relative to the other star.

"We had reached the data limit existing, so we had to turn to a different observational strategy to decide between the two scenarios proposed by the two teams, ”said KU Leuven researcher Abigail Frost, who led the new study on Astronomy & Astrophysics.

if (jQuery ("# ​​crm_srl-th_scienze_d_mh2_1"). is (": visible")) {console.log ("Edinet ADV adding zone: tag crm_srl-th_scienze_d_mh2_1 slot id: th_scienze_d_mh2"); } To solve the mystery, the two teams worked together to obtain new, sharper HR 6819 data using ESO's Very Large Telescope (VLT) and Very Large Telescope Interferometer (VLTI). "The VLTI was the only facility that would provide us with the crucial data we needed to extricate ourselves between the two explanations," said Dietrich Baade, author of both the original HR 6819 study and the new Astronomy and Astrophysics paper. Since it made no sense to ask for the same observation twice, the two teams joined forces, which allowed them to pool their resources and knowledge to find the true nature of this system.

Artist's impression of a supermassive black hole at the center of a galaxy “The scenarios we were looking for were quite clear, very different and easily distinguishable with the right tool,” explained Rivinius. "We agreed that there were two light sources in the system, so the question was whether they orbited each other closely, as in the stripped star scenario, or were they very far from each other. , as in the black hole scenario ".

if (jQuery (" # crm_srl-th_scienze_d_mh3_1 "). is (": visible ")) {console.log (" Edinet ADV adding zone: tag crm_srl-th_scienze_d_mh3_1 slot id: th_scienze_d_mh3 "); } 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 light companion in a wider orbit, while GRAVITY's high spatial resolution was able to resolve two light sources separated by only one third of the distance between the Earth and the Sun, ”said Frost. “This data turned out to be the final piece of the puzzle and allowed us to conclude that HR 6819 is a binary system with no black holes.”

“Our best interpretation so far is that we have captured this binary system in a moment shortly after one of the stars had sucked up the atmosphere from its companion star. This is a common phenomenon in close binary systems, sometimes referred to as 'stellar vampirism' in the press, ”explained Bodensteiner, now a member of ESO in Germany and author of the new study. "As the donor star was stripped of some of its material, the receiving star began to rotate more rapidly."

"Capturing such a post-interaction phase is extremely difficult as it is so short," he said. added Frost. “This makes our findings for HR 6819 very exciting, as it presents a perfect candidate for studying how this vampirism affects the evolution of massive stars and, in turn, the formation of their associated phenomena, including gravitational waves and violent explosions. di supernova ".

if (jQuery (" # crm_srl-th_scienze_d_mh4_1 "). is (": visible ")) {console.log (" Edinet ADV adding zone: tag crm_srl-th_scienze_d_mh4_1 slot id: th_scienze_d_mh4 " ); } The new joint Leuven-ESO team now plans to monitor HR 6819 more closely using the VLTI's GRAVITY tool. The researchers will conduct a joint study of the system over time, to better understand its evolution, limit 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 due to their nature," said Rivinius. "But estimates of the order of magnitude suggest that there are tens to hundreds of millions of black holes in the Milky Way alone," Baade added. It is only a matter of time before astronomers discover them.

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