A team of international experts renowned for debunking several black hole discoveries have discovered a stellar-mass black hole in the Large Magellanic Cloud, a neighboring galaxy to ours. “For the first time, our team came together to report on the discovery of a black hole, rather than rejecting one,” said study leader Tomer Shenar. What’s more, they discovered that the star behind the black hole had disappeared without any signs of a powerful explosion. The discovery was made thanks to six years of observations obtained with the Very Large Telescope (VLT) of the European Southern Observatory (ESO).
“We identified a ‘needle in a haystack,'” says Shenar who started the study at KU Leuven in Belgium.  and is now a Marie Curie Fellow at the University of Amsterdam, the Netherlands. Although other similar black hole candidates[ have been] – https://www.eso.org/public/news/eso2116/ proposed, the team says it is the first “dormant” stellar-mass black hole to be unambiguously detected outside our galaxy.
Stellar-mass black holes form when massive stars reach the end of their lives and collapse under their own gravity. In a binary, a system of two stars revolving around each other, this process leaves behind an orbiting black hole with a bright companion star. The black hole is “dormant” if it does not emit high levels of X-ray radiation, which is how such black holes are usually detected. “It’s incredible that we barely know about dormant black holes, given how much astronomers believe them to be,” says co-author Pablo Marchant of KU Leuven. The newly discovered black hole is at least nine times the mass of our Sun and orbits a hot blue star weighing 25 times the mass of the Sun.
Dormant black holes are particularly difficult to spot because they interact little with their environment. “For more than two years now, we have been searching for such black hole binary systems,” says co-author Julia Bodensteiner, a researcher at ESO in Germany. “I was very excited when I heard about VFTS 243, which in my opinion is the most compelling candidate reported to date.” 
To find VFTS 243, the collaboration searched nearly 1,000 massive stars in the Tarantula Nebula region of the Large Magellanic Cloud, looking for any that might have black holes as companions. It is extremely difficult to identify these companions as black holes, since there are many alternative possibilities.
“As a researcher who has [debunked] – https://www.eso.org/public/news/eso2204/ potential black holes in recent years, I was extremely skeptical of this discovery,” Shenar says. The skepticism was shared by co-author Kareem El-Badry of the Center for Astrophysics | Harvard & Smithsonian in the United States, which Shenar calls the “black hole destroyer”. “When Tomer asked me to double-check his findings, I had my doubts. But I couldn’t find a plausible explanation for the data that didn’t implicate a black hole,” says El-Badry.
The discovery also allows the team to have a unique view of the processes that accompany the formation of black holes. Astronomers believe a stellar-mass black hole forms when the core of a dying massive star collapses, but whether or not this is accompanied by a powerful supernova explosion remains unclear.
“The star that formed the black hole in VFTS 243 appears to have collapsed entirely, with no signs of a previous explosion,” Shenar says. “Evidence for this ‘direct collapse’ scenario has emerged recently, but our study provides arguably one of the most direct indications. This has huge implications for the origin of black hole mergers in the cosmos.
The black hole in VFTS 243 was found using six years of observations of the Tarantula Nebula by the Wide Fiber Array Multi-Element Spectrograph ([FLAMES] – https://www.eso.org/public/teles-instr/paranal-observatory/vlt/vlt-instr/flames/ ) instrument on ESOs[ VLT] – https://www.eso.org/public/teles-instr/paranal-observatory/vlt/ .
Despite the nickname “black hole police,” the team actively encourages scrutiny and hopes their work, published today in Nature Astronomy, will lead to the discovery of other stellar-mass black holes orbiting Earth. massive stars, thousands of which are expected to exist in the Milky Way and the Magellanic Clouds.
“Of course, I expect others in the field to carefully consider our analysis and try to concoct alternative models,” concludes El-Badry. “It’s a very exciting project to be involved in.”
 The work was carried out in the team led by Hugues Sana at the Institute of Astronomy of KU Leuven.
 A separate study led by Laurent Mahy, involving several of the same team members and accepted for publication in Astronomy & Astrophysics, reports on another promising stellar-mass black hole candidate, in system HD 130298 in our own galaxy. , the Milky Way.
 The observations used in the study cover approximately six years: they consist of data[ VLT FLAMES Tarantula Survey] – https://www.eso.org/sci/publications/messenger/archive/no.145-sep11/messenger-no145-33-38.pdf (edited by Chris Evans, United Kingdom Astronomy Technology Centre, STFC, Royal Observatory , Edinburgh; now at the European Space Agency) obtained from 2008 and 2009, and additional data from the[ Tarantula Massive Binary Monitoring] – https://www.aanda.org/articles/aa/full_html/2017/02/aa29844-16/aa29844-16.html program (directed by Hugues Sana, KU Leuven), obtained between 2012 and 2014.
This research was presented in an article titled “An X-ray quiet black hole born with a negligible kick in a massive binary of the Large Magellanic Cloud” to be published in Nature Astronomy (doi: 10.1038/s41550-022-01730-y) .
The research leading to these results has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreement numbers 772225: MULTIPLE) (PI: Sana).
The team is composed of T. Shenar (Institute of Astronomy, KU Leuven, Belgium [KU Leuven]; Anton Pannekoek Institute of Astronomy, University of Amsterdam, Amsterdam, Netherlands [API]), H. Sana (KU Leuven), L. Mahy (Royal Observatory of Belgium, Brussels, Belgium), K. El-Badry (Center for Astrophysics | Harvard & Smithsonian, Cambridge, USA [CfA]; Harvard Society of Fellows, Cambridge, USA; Max Planck Institute for Astronomy, Heidelberg, Germany [MPIA]), P. Marchant (KU Leuven), N. Langer (Argelander-Institut für Astronomie der Universität Bonn, Germany, Max Planck Institute for Radio Astronomy, Bonn, Germany [MPIfR]), C. Hawcroft (KU Leuven), M. Fabry (KU Leuven), K. Sen (Argelander-Institut für Astronomie der Universität Bonn, Germany, MPIfR), LA Almeida (Universidade Federal do Rio Grande do Norte, Natal, Brazil Universidade do Estado do Rio Grande do Norte, Mossoró, Brazil), M. Abdul-Masih (ESO, Santiago, Chile), J. Bodensteiner (ESO, Garching, Germany), P. Crowther (Department of Physics and Astronomy , University of Sheffield, UK), M. Gieles (ICREA, Barcelona, Spain; Institut de Ciències del Cosmos, Universitat de Barcelona, Barcelona, Spain), M. Gromadzki (Astronomical Observatory, University of Warsaw, Poland [Warsaw]), V. Henault-Brunet (Department of Astronomy and Physics, Saint Mary’s University, Halifax, Canada), A. Herrero (Instituto de Astrofísica de Canarias, Tenerife, Spain [IAC]; Department of Astrophysics, University of La Laguna, Tenerife, Spain [IAC-ULL]), A. de Koter (KU Leuven, API), P. Iwanek (Warsaw), S. Kozłowski (Warsaw), DJ Lennon (IAC, IAC-ULL), J. Maíz Apellániz (Centro de Astrobiología, CSIC-INTA, Madrid, Spain), P. Mróz (Warsaw), AFJ Moffat (Department of Physics and Institute for Research on Exoplanets, University of Montreal, Canada), A. Picco (KU Leuven), P. Pietrukowicz (Warsaw), R. Poleski (Warsaw), K. Rybicki (Warsaw and Department of Particle Physics and Astrophysics, Weizmann Institute of Science, Israel), FRN Schneider (Heidelberg Institute for Theoretical Studies, Heidelberg, Germany [HITS]; Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Heidelberg, Germany), DM Skowron (Warsaw), J. Skowron (Warsaw), I. Soszyński (Warsaw), MK Szymański (Warsaw), S. Toonen (API), A. Udalski (Warsaw), K. Ulaczyk (Department of Physics, University of Warwick, UK), JS Vink (Armagh Observatory & Planetarium, UK) and M. Wrona (Warsaw).
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