{"text":[[{"start":6.65,"text":"The writer is a science commentator"}],[{"start":9.2,"text":"The giveaway was not so much what was there — but what was missing. When astronomers looked closely at the cold molecular gas shrouding the supermassive black hole at the heart of our own galaxy, the Milky Way, they found a vast blank gap. "}],[{"start":24.95,"text":"From the lip of the monstrous black hole, called Sagittarius A*, a large cone of nothingness funnelled outwards. This, researchers announced last week, is long-sought evidence of a hot breeze flowing outwards from the black hole and sweeping away the cold gas in its path, and one that has been blowing for around 20,000 years. "}],[{"start":46.2,"text":"The gravitational pull of a black hole, whatever its size, is so intense that not even light can escape once trapped. That makes it impossible to see directly; its presence is inferred from the behaviour of other nearby objects, such as stars orbiting around it. But black holes have also been theorised to spit material out, in the form of jets or winds."}],[{"start":68.1,"text":"The latest findings confirm that our nearest supermassive black hole, heavier than four million suns and the anchor of our own galaxy, behaves in line with expectation, by flinging out material as well as sucking it in. The finding comes with a certain irony: it can take the most complex of astronomical analyses to expose the ordinariness of our own galactic neighbourhood."}],[{"start":90.89999999999999,"text":"Black holes are born when massive stars have burnt through their fuel and collapsed inwards (at the centre of every black hole, goes the theory, lies an infinitely small and dense point called a “singularity”). While classifications are somewhat elastic, a black hole is generally classed as supermassive when it exceeds 100,000 times the mass of our own Sun. "}],[{"start":114.29999999999998,"text":"Each large galaxy is thought to have a supermassive black hole at its heart; Sagittarius A*, lying around 26,000 light years away, is the stellar corpse at the heart of our spiral galaxy."}],[{"start":126.79999999999998,"text":"Winds emerging from other supermassive black holes have been observed, including in the galaxy M87, which lies 53mn light years away. But confirmation for Sagittarius A* has until now proven elusive. The view from Earth is blocked by dust, gas and debris; our nearest supermassive black hole is also in a relatively inactive phase of life known as a quiescent state, making it hard to read. Previous observations have given inconclusive results. "}],[{"start":156.49999999999997,"text":"Astronomer Mark Gorski and astrophysicist Lena Murchikova from Northwestern University turned to the Alma radio telescope in northern Chile. The telescope, comprising 66 radio antennas, is designed to harvest the faint light from the “cool” universe, made up of extended colder structures, like molecular gas (mostly hydrogen) and dust clouds. These are harder to see than hot, bright objects like stars. The researchers looked at five years of observations of the cold molecular gas within one parsec (about three light years) of the centre of the black hole, blotting out its radio emissions to lay bare the pattern of frigid gas clumped around it."}],[{"start":198.2,"text":"A conical clearing with sharp edges sprang into view, consistent with a hot breeze from the black hole sweeping away cold gas. Murchikova told me they felt disbelief at seeing “such a large and well-defined wind cone . . . we just stared at it for a while in silence”. They cross-checked their results using Nasa’s Chandra X-ray Observatory, and published their findings last week in The Astrophysical Journal Letters."}],[{"start":222.79999999999998,"text":"Martin Rees, the Cambridge university astronomer who co-wrote a landmark 1971 paper predicting a supermassive black hole at the centre of our galaxy, cautiously welcomed the work, telling me it improved on previous attempts to find such a wind: “The authors present amazingly detailed maps of the gas and dust near the galactic centre and show how this yields insights into the huge black hole that lurks there.” "}],[{"start":248.95,"text":"Rees wondered about other possible explanations; the researchers counter that alternative scenarios, such as heat or wind coming from a supernova explosion or from the stars orbiting the black hole, do not match observations. "}],[{"start":263.15,"text":"One of the biggest surprises, Murchikova says, is that the wind is steady rather than explosive: “We have never seen a breeze from a black hole . . . Seeing the black hole sitting there, being quiet, but still dumping energy all over the region without doing anything violent, is terribly cute.” The important message, she stresses, is that black holes actively shape their surroundings."}],[{"start":284.34999999999997,"text":"It is cheering to think of Sagittarius A* as our very own galactic grande dame, not quite dead and gone but still delivering her own breezy performance in the twilight of a long cosmic career."}],[{"start":298.34999999999997,"text":"This article has been amended to clarify that Sagittarius A* is Earth’s nearest supermassive black hole, not the nearest black hole."}],[{"start":314.65,"text":""}]],"url":"https://audio.ftcn.net.cn/album/a_1781568530_8959.mp3"}