Astronomers have found a black hole in our cosmic backyard
Almost but not quite in time for Halloween, astronomers announced their discovery on Friday the closest known black hole. It’s a great, yawning shell of emptiness 10 times more massive than the sun, orbiting as far from its star as Earth is from ours.
Don’t worry, though: this black hole is 1,600 light-years away, in the constellation of the Serpent; the next closest known black hole is about 3,000 light-years away in the constellation Monocera. What sets this new black hole apart from the thousands of others already identified in our Milky Way galaxy, aside from its proximity, is that it does nothing – it doesn’t pull a nearby star to its doom, it doesn’t gravitationally consume everything nearby. Instead, the black hole sits dormant, a silent killer waiting for space currents to feed on it.
Black holes are objects so dense that, according to Einstein’s theory of general relativity, not even light can escape them. This makes them the most intriguing and violent phenomena in nature; when fed, they can become the brightest objects in the universe, as gas, dust, and even smaller stars rip apart and heat to incandescence, spewing energy as they approach the gates of eternity.
Most every galaxy has a supermassive black hole millions of billions of times the size of the Sun; scientists aren’t sure where they come from. Smaller black holes are thought to form from massive stars that have reached the end of their thermonuclear lives 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 two-star systems.
But what about the dormant holes, the ones that aren’t currently coughing up 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 studying data from the European Space Agency’s GAIA spacecraft, which tracked the positions, motions and other properties of millions of stars in the Milky Way with extraordinary precision.
dr. el-Badry and his team discovered a star, virtually identical to our sun, that was quivering strangely, as if under the gravitational influence of an invisible companion. To investigate further, the researchers deployed the Gemini North telescope atop Mauna Kea in Hawaii, which was able to 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 astronomers use to analyze the wobbles of stars to detect the presence of exoplanets in orbit – except this time the quarry was much larger.
Their results and subsequent calculations were consistent with a 10-solar-mass black hole surrounded by a star similar to ours. They named 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 from the National Optical and Infrared Laboratory, which runs the Gemini North telescope.
“This is the closest known black hole with a factor of three, and its discovery indicates the existence of a substantial population of dormant black holes in binary systems,” he and his co-authors wrote. in paper published Wednesday in the Monthly Notices of the Royal Astronomical Society. Astronomers said the new discovery raised questions about their assumed 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 leading theories, the star’s death and subsequent formation of a black hole would involve a supernova explosion and other processes that would severely disrupt another, smaller star in the system. So why does the second star look so normal?
“It raises a lot of questions about how this binary system was formed,” said Dr. el-Badry in a press release, “as well as how many of these dormant black holes are out there.”
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