A team of researchers – known as the “black hole police” because they have debunked so many black hole discoveries – searched for nearly 1,000 stars in the Tarantula Nebula in the constellation Dorado before spotting it. They claim that this is the first dormant “stellar mass” black hole to be detected outside of our Milky Way Galaxy. Stellar mass black holes form when massive stars reach the end of their lives and collapse under their own gravity. A black hole is described as “dormant” if it is not actively gobbling up matter and therefore does not emit light or other radiation. The discovery has been likened to finding a “needle in a haystack”, as quiescent black holes are notoriously difficult to detect because they do not interact with their surroundings. Co-author Dr Pablo Marchant of KU Leuven in Belgium, said: “It’s incredible, we know of almost no latent black holes given how common astronomers think they are.” An artist’s impression of the binary system VFTS 243. The system, located in the Tarantula Nebula in the Large Magellanic Cloud, consists of a hot, blue star with a mass 25 times the mass of the Sun and a black hole, which is at least nine times the mass of the Sun Artist’s impression of the binary system VFTS 243. The background image shows a Visible and Infrared Survey Telescope for Astronomy (VISTA) image of a portion of the Large Magellanic Cloud, marking the region in which VFTS 243 is located. The sizes of star, black hole and orbits are not to scale
WHAT IS A “BINARY SYSTEM”?
A binary star is a system of two stars that are gravitationally bound and orbit each other. One or both stars in the system could be a black hole. When this happens, they are often identified by the presence of bright X-ray emissions. X-rays are produced when matter falls from one component, called the donor (usually a relatively normal star), into the other component, called the accretor (the black hole). The matter forms in a glowing accretion disk that swirls around the black hole. However, observations from NASA’s Chandra X-ray telescope reveal that VFTS 243 is X-ray faint. The newly discovered black hole is located in the Large Magellanic Cloud – a satellite galaxy neighboring the Milky Way. The Large Magellanic Cloud orbits a hot, blue star that is nearly three times the size of our galaxy. Thousands of stellar-mass black holes are believed to exist in our Milky Way and the Magellanic Clouds. They are much smaller than the supermassive black hole 27,000 light-years from Earth that powers our Milky Way, known as Sagittarius A*. The black hole is part of a “binary” with a bright companion star, where they orbit each other in a system known as VFTS 243. Co-author Dr Julia Bodensteiner, of the European Southern Observatory (ESO) in Germany, said: “We have been looking for such black hole-binary systems for more than two years now. “I was very excited to hear about VFTS 243, which in my opinion is the most convincing candidate reported to date.” It took six years worth of data from ESO’s Very Large Telescope (VLT) to officially identify VFTS 243. The FLAMES (Fibre Large Array Multi Element Spectrograph) scanner on the VLT enables the observation of more than a hundred objects simultaneously. Historically, binaries hosting stellar-mass black holes have been identified through the presence of bright X-ray emission from the accretion disk. The glowing accretion disk consists of gases from the atmosphere of the living star that flow towards and surround the black hole. However, observations from NASA’s Chandra X-ray telescope reveal that VFTS 243 is X-ray faint. This image from the VLT Survey Telescope at ESO’s Paranal Observatory in Chile shows the Tarantula Nebula and its surroundings within the Large Magellanic Cloud. Shows star clusters, glowing clouds of gas and scattered remnants of supernova explosions Historically, binaries hosting stellar-mass black holes have been identified through the presence of bright X-ray emission from the accretion disk (image). The bright accretion disk consists of gases from the atmosphere of the living star that flow toward and surround the black hole (stock image) The study, published today in Nature Astronomy, also sheds light on how black holes are formed from the cores of dying stars. The star that gave rise to VFTS 243 appears to have completely collapsed, leaving no trace of a powerful supernova explosion. Dr Shenar explained: “Evidence for this ‘instant collapse’ scenario has only recently emerged – but our study arguably provides one of the most direct clues. “This has huge implications for the origin of black hole mergers in the world.” It took six years worth of data from ESO’s Very Large Telescope (pictured) to identify VFTS 243 The FLAMES instrument, mounted on the Nasmyth A platform at ESO’s Very Large Telescope. FLAMES is a high-resolution spectrograph of the VLT and can access targets over a large corrected field of view. It allows the observation of more than a hundred objects at the same time Artist rendering of NASA’s Chandra X-ray Observatory space telescope Despite the nickname “black hole police”, the international team of researchers actively encourages scrutiny of their work. Lead author Dr Tomer Shenar, of the University of Amsterdam, said: “As a researcher who has been debunking possible black holes for the past few years, I was extremely skeptical about this discovery. “For the first time, our team has come together to report a black hole discovery – rather than dismiss it.” Dr. Kareem El-Badry of Harvard University in Boston is nicknamed the “black hole destroyer” because of his reputation for debunking discoveries. Dr El-Badry said: “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 involve a black hole. “Of course I expect others in the field to look carefully at our analysis and try to build alternative models. “It’s a very exciting project to be a part of.”
WHAT IS INSIDE A BLACK HOLE?
Black holes are strange objects in the universe that get their name from the fact that nothing can escape their gravity, not even light. If you venture too close and cross the so-called event horizon, the point from which no light can escape, you will be trapped or destroyed. For small black holes, you would never survive such a close approach anyway. Tidal forces near the event horizon are enough to stretch any matter until it’s just a string of atoms, in a process physicists call “spaghettitting.” But for large black holes, such as the supermassive objects in the cores of galaxies like the Milky Way, which weigh tens of millions, if not billions, of times the mass of a star, crossing the event horizon would be smooth. Because it should be possible to survive the transition from our world to the black hole world, physicists and mathematicians have long wondered what that world would look like. They have turned to Einstein’s equations of general relativity to predict the world inside a black hole. These equations work well until an observer reaches the center or singularity, where, in theoretical calculations, the curvature of spacetime becomes infinite.
