Is Planet Nine a Black Hole?


    “Astrophysicists have recently begun hatching plans to find out just how weird Planet Nine might be,” reports the New York Times. Long-time Slashdot reader fahrbot-bot shares their report: Although it is probably wishful thinking, some astronomers contend that a black hole may be lurking in the outer reaches of our solar system. All summer, they have been arguing over how to find it, if indeed it is there, and what to do about it, proposing plans that are only halfway out of this world… Earlier this year, Edward Witten, a theoretical physicist at the Institute for Advanced Study in Princeton, chimed in… Dr. Witten suggested borrowing a trick from Breakthrough Starshot, the proposal by Russian philanthropist Yuri Milner and Dr. Hawking to send thousands of laser-propelled microscopic probes to the nearest star system, Alpha Centauri. Dr. Witten suggested sending hundreds of similarly small probes outward in all directions to explore the solar system. By keeping track of incoming signals from the probes, scientists on Earth would be able to tell if and when each one sped up or slowed down as it encountered the gravitational field of Planet Nine or anything else out there. Key to this plan would be the ability of the probes to keep pinging Earth precisely every hundred-thousandth of a second. In May, astronomers Scott Lawrence and Zeeve Rogoszinski of the University of Maryland suggested instead monitoring the trajectories of the probes with high-resolution radio telescopes, which would obviate the need for high-precision clocks on the probes. Another idea came from Avi Loeb, chair of the astronomy department at Harvard and leader of a scientific advisory board for Breakthrough Starshot: in July Dr. Loeb was back, with a student, Amir Siraj, and a new idea for finding the Planet Nine black hole. If a black hole were out there, they argued, it would occasionally rip apart small comets, causing bright flares that could soon be spotted by the new Vera C. Rubin Observatory, previously known as the Large Synoptic Survey Telescope, now under construction in Chile. The observatory’s mission, starting in 2021, is to make a movie of the universe, producing a panorama of the entire southern night sky every few days and revealing anything that has changed or moved. Such flares should occur a few times a year, they noted. “Our calculations show that the flares will be bright enough for the Vera Rubin Observatory to rule out or confirm Planet Nine as a black hole within one year of monitoring the sky with its L.S.S.T. survey,” Dr. Loeb wrote in an email. Moreover, because the Rubin telescope examines such a large swath of sky, it could detect or rule out black holes of similar size all the way out to the Oort cloud, a vague and diffuse assemblage of protocomets and primordial, frozen riffraff a trillion miles from the sun, they said. The prospect of finding a black hole in our own solar system “is as startling as finding evidence that someone might be living in the shed in your backyard,” Dr. Loeb said in the email. “If so, who is it, and how did it get there?” Read more of this story at Slashdot.


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