US, WASHINGTON (ORDO NEWS) — A team of astronomers from the European Southern Observatory (ESO) and other institutes discovered a black hole located just 1000 light-years from Earth. The black hole is closer to our solar system than any other found to date, and is part of a triple system that can be seen with the naked eye.
The team found evidence of an invisible object by tracking its two companion stars with the 2.2-meter MPG / ESO telescope at ESO La Silla Observatory in Chile. They say that this system can only be the tip of the iceberg, as many similar black holes can be found in the future.
“We were completely surprised when we realized that this is the first stellar system with a black hole that can be seen with the naked eye,” says Petr Hadrava, Honored Worker of the Czech Republic Academy of Sciences in Prague and co-author of the study. Located in the constellation Telescope, the system is so close to us that its stars can be seen from the southern hemisphere on a clear, dark night without binoculars or a telescope.
“This system contains the black hole closest to Earth that we know about,” says ESO scientist Thomas Rivinius, who led the study published today in Astronomy & Astrophysics.
The team initially oversaw a system called HR 6819 as part of a study of two-star systems. However, analyzing their observations, they were stunned to find a third, previously unknown body in HR 6819: a black hole. Observations with the FEROS spectrograph at the 2.2-meter MPG / ESO telescope at La Silla showed that one of the two visible stars rotates around an invisible object every 40 days, while the second star is at a great distance from this inner pair.
Dietrich Baade, ESO Honorary Astronomer in Garching and co-author of the study, says: “The observations needed to determine the 40 day period were distributed over several months. This was only possible thanks to the innovative ESO service surveillance scheme.”
The hidden black hole in HR 6819 is one of the very first stellar mass black holes found that do not interact with the environment and therefore look truly black. But the team can determine its presence and calculate its mass by studying the star’s orbit in the inner pair. “An invisible object, whose mass is 4 times the mass of the Sun, can only be a black hole,” concludes Rivinius, based in Chile.
To date, astronomers have discovered only a couple of dozen black holes in our galaxy, almost all of which interact strongly with the environment and make their presence known by emitting powerful x-rays in this interaction. But scientists have estimated that during the existence of the Milky Way, many other stars went into black holes after the end of their lives. The discovery of a quiet, invisible black hole in HR 6819 gives clues about where many hidden black holes in the Milky Way might be.
“There should be hundreds of millions of black holes, but we know only very few. Knowing what to look for should help us search for them better, ”says Rivinius. Baade adds that finding a black hole in a ternary system so closely indicates that we only see “the tip of an exciting iceberg”.
Astronomers already believe that their discovery can shed light on the second system. “We realized that another system, called LB-1, could also be such a triple, although we need more observations to say for sure,” said Marianne Heida, ESO Researcher and co-author of the article. “LB-1 is a little farther from Earth, but still pretty close in astronomical terms, so that means there are probably a lot more of these systems.
Having found and studied them, we can learn a lot about the formation and evolution of these rare stars that begin their lives with a mass of about 8 solar masses and end with a supernova explosion that leaves a black hole.”
The discoveries of these triple systems with an inner pair and a distant star can also give clues about violent cosmic mergers that emit gravitational waves powerful enough to be detected on Earth. Some astronomers believe that mergers can occur in systems with a configuration similar to HR 6819 or LB-1, but where the inner pair consists of two black holes or a black hole and a neutron star.
Although HR 6819 and LB-1 have only one black hole and do not have neutron stars, these systems can still help scientists understand how stellar collisions occur in triple star systems.
This study was presented in the article “Triple System with the naked eye with a non-accrediting black hole in the internal binary system”, published today in the journal Astronomy & Astrophysics.
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