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We\u2019ve seen the waterfall of matter plunging into a black hole<\/p>\n
Buradaki \/ Alamy Stock Photo<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
A strange area around black holes called the \u201cplunging region\u201d has been spotted for the first time. This area, where matter stops circling a black hole and instead falls straight in, was predicted by Albert Einstein\u2019s theory of general relativity, but it has never been observed before. Studying plunging regions could teach us about how black holes form and evolve, as well as reveal new information about the fundamental nature of space-time.<\/p>\n
When any matter gets too close to a black hole, it rips apart and forms an orbiting ring around it called an accretion disc. General relativity predicts there should be an inner boundary to the accretion disc past which nothing can orbit the black hole \u2013 instead, it should plunge straight in, rapidly accelerating to near the speed of light as it falls.<\/p>\n
\u201cIt\u2019s like a river turning into a waterfall, and until now we\u2019ve only been looking at the river,\u201d says Andrew Mummery at the University of Oxford. \u201cIf Einstein was wrong, then it would be stable all the way down \u2013 there would only be a river.\u201d Now we\u2019ve gotten our first peek at the waterfall, suggesting Einstein was correct.<\/p>\n
<\/p>\n Mummery and his colleagues spotted evidence of the plunging region around a black hole in a binary system called MAXI J1820+070, which is about 10,000 light years from Earth. They used data from the Nuclear Spectroscopic Telescope Array (NuSTAR), a space-based X-ray telescope, to build models of the light from the black hole\u2019s accretion disc.<\/p>\n They found the models only fit the data when they included the light emitted by matter in the plunging region in addition to light from the accretion disc. \u201cBefore, we sort of thought that anything that crosses this boundary would have no time to really radiate appreciably before it plunges into the black hole\u201d, so researchers wouldn\u2019t see anything, says Greg Salvesen at Los Alamos National Laboratory in New Mexico, who was not involved with this work. \u201cBut it turns out that this plunging region gives you extra light that you wouldn\u2019t have expected.\u201d<\/p>\n This extra light could solve a long-standing problem in X-ray astronomy, in which black holes appear to be spinning faster than theory predicts. The spin of a black hole and the brightness of the area around it are connected, so adding some extra light could bring the spins back in line with predictions. \u201cBlack hole spins tell us about all kinds of things, so if we could measure it better, we could answer loads of questions in astrophysics,\u201d says Salvesen.<\/p>\n That includes questions about the nature of gravity and space-time itself, because plunging regions are some of the most extreme regions of space we can observe. The plunging region is just outside the event horizon, beyond which the gravitational forces are so strong, no matter or even light can escape.<\/p>\n \u201cTechnically, if the matter had a rocket it could escape the plunging region, but it\u2019s doomed \u2013 its orbit has become unstable and it\u2019s rapidly accelerating toward the speed of light,\u201d says Mummery. \u201cThis stuff has about as much chance of coming back as water off the edge of a waterfall.\u201d The researchers are now trying to make more observations of these strange cosmic waterfalls to illuminate the conditions in these extraordinary areas.<\/p>\n Topics:<\/p>\n<\/section><\/div>\n