Astronomers discover 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 gaping vacuum shell 10 times more massive than the sun, orbiting as far from its own star as Earth is from ours.

But don’t worry: this black hole is 1,600 light-years away, in the constellation of Ophiuchus; the next closest known black hole is about 3,000 light-years away in the constellation of Monoceros. What distinguishes this new black hole from the twenty others already identified in our Milky Way galaxy, besides its proximity, is that it does nothing – does not attract the nearby star to its doom, does not gravitationally consumes everything nearby. Rather, the black hole is dormant, a silent killer waiting for the currents of space to feed it.

Black holes are such dense objects 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 they feed, they can become the brightest objects in the universe, as gas, dust, and even smaller stars are torn apart and heated to incandescence, spewing energy at the approaches the gates of eternity.

Most galaxies have a supermassive black hole millions of billions of times more massive than the sun; scientists don’t know where they come from. Smaller black holes are thought to form from massive stars that have 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 spit as they remove the gas from their companions in double star systems.

But what about dormant holes, those that are not currently breathing fire? Kareem El-Badry, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics, has been searching for these hidden demons for four years. He found this black hole by examining data from the European Space Agency’s GAIA spacecraft, which tracked with exquisite precision the positions, movements and other properties of millions of stars in the Milky Way.

Dr. El-Badry and his team have detected a star, virtually identical to our sun, which quivers strangely, as if under the gravitational influence of an invisible companion. To further their research, the researchers commandeered the Gemini North telescope atop Mauna Kea in Hawaii, which could measure the speed and period of this oscillation and thus determine the relative masses of the objects involved. The technique is identical to the process by which astronomers analyze the oscillations of stars to detect the presence of orbiting exoplanets – except this time the quarry was much larger.

Their subsequent results and calculations were consistent with a 10-solar-mass black hole circled by a star similar to our own. 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 National Optical and InfraRed press release. Laboratory, which operates the Gemini North Telescope.

“This is the closest known black hole by a factor of three, and its discovery suggests the existence of a large population of dormant black holes in binaries,” he and his co-authors wrote in a paper. published Wednesday in the Monthly Notices of the Royal Astronomical Society. The astronomers said the new discovery raises questions about their presumed knowledge of the evolution of these binary star systems. The ancestor of this black hole must have been a star of about 20 solar masses. According to leading theories, the star’s death and subsequent black hole formation involved a supernova explosion and other processes that severely disrupted the other, smaller star in the system. So why does the other star seem so normal?

“This raises many questions about how this binary system was formed,” Dr. El-Badry said in the press release, “as well as how many of these dormant black holes are out there.”