Astronomers find a black hole in our cosmic backyard
Almost, but not quite in time for Halloween, astronomers announced on Friday that they had discovered the closest known black hole. It’s a biggie, a shell of gaping emptiness 10 times the mass of the sun, orbiting as far from its own star as the Earth does from ours.
But don’t worry: This black hole is 1,600 light-years away, in the constellation Ophiuchus; the next known black hole is about 3,000 light-years away in the constellation Monoceros. What sets this new black hole apart from the thousands of others already identified in our Milky Way Galaxy, besides its proximity, is that it doesn’t do anything – doesn’t pull the nearby star to its demise, doesn’t gravitate to everything nearby. Rather, the black hole is dormant, a silent killer waiting for the streams of space to feed it.
Black holes are objects so dense that, according to Einstein’s general theory of relativity, not even light can escape them. This makes them the most intriguing and violent phenomena in nature; when they feed, they can become the most brilliant objects in the universe as gas, dust and even smaller stars are shredded and heated to glowing energy as they approach the gates of eternity.
Almost every galaxy has a supermassive black hole that is millions of billions of times more massive than the Sun; scientists aren’t sure where they come from. Smaller black holes are thought to have formed from massive stars that reached the end of their thermonuclear life and collapsed. There are probably millions of black holes in the Milky Way. They usually make themselves known by the X-rays they spew as they strip gas from their companions in binary star systems.
But what about dormant holes, which are not currently coughing fire? Kareem el-Badry, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, has been searching for such hidden demons for four years. He found this black hole by closely examining data from the European Space Agency’s GAIA spacecraft, which has tracked with extraordinary precision the positions, motions and other properties of millions of stars in the Milky Way.
dr. el-Badry and his team discovered a star, almost identical to our sun, that trembled strangely, as if under the gravitational pull of an unseen companion. To investigate further, the researchers seized the Gemini North telescope atop Mauna Kea in Hawaii, which could measure the speed and period of this wobble to determine the relative masses of the objects involved. The technique is identical to the process by which astronomers analyze the wobble of stars to detect the presence of orbiting exoplanets – except this time the quarry was much larger.
Their results and subsequent calculations matched a 10 solar mass black hole surrounded by a star similar to our own. They called it Gaia BH1.
“Take the solar system, put a black hole where the sun is and the sun where the earth is, and you get this system,” Dr. el-Badry said in a press release of the National Optical and InfraRed Laboratory, which runs the Gemini North Telescope.
“This is the closest known black hole by a factor of three, and its discovery suggests the existence of a significant population of dormant black holes in binary numbers,” he and his co-authors wrote. in a newspaper published Wednesday in the Monthly Notices of the Royal Astronomical Society. Astronomers said the new discovery raised questions about their supposed knowledge of how such binary star systems evolved. The progenitor of this black hole must have been a star of about 20 solar masses. According to the leading theories, the death of the star and the subsequent formation of a black hole would have led to a supernova explosion and other processes that would have severely disrupted the other, smaller star in the system. So why does the other star seem so normal?
“It raises a lot of questions about how this binary system was formed,” said Dr. el-Badry in the press release, “and also about how many of these sleeping black holes there are.”
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