Astronomers Find a Black Hole in Our Cosmic Back Yard

Almost but not quite in time for Halloween, astronomers announced on Friday that they had discovered the closest known black hole. It is a biggie, a shell of yawning emptiness 10 times as massive as the sun, orbiting as far from its own star as the Earth is from ours. From a report: Not to worry, however: This black hole is 1,600 light-years away, in the constellation Ophiuchus; the next nearest known black hole is about 3,000 light-years away in the constellation Monoceros. What sets this new black hole apart from the 20 or so others already identified in our Milky Way galaxy, besides its proximity, is that it isn't doing anything -- not drawing the nearby star to its doom, not gravitationally consuming everything nearby. Rather, the black hole is dormant, a silent killer waiting for the currents of space to feed it. 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 scrutinizing data from the European Space Agency's GAIA spacecraft, which has been tracking with exquisite precision the positions, motions and other properties of millions of stars in the Milky Way. Dr. El-Badry and his team detected a star, virtually identical to our sun, that was jittering strangely, as if under the gravitational influence of an invisible companion. To investigate further, the researchers commandeered the Gemini North telescope atop Mauna Kea in Hawaii, which could measure the speed and period of this wobble and thus determine the relative masses of the objects involved. The technique is identical to the process by which astronomers analyze the wobbles of stars to detect the presence of orbiting exoplanets -- except this time the quarry was far bigger. Their results and subsequent calculations were consistent with a black hole of 10 solar masses being circled by a star similar to our own. They named it Gaia BH1.

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