These X-ray pulses take 300 years to traverse the distance between the central black hole and a large cloud known as Sagittarius B2, so the cloud responds to events that could have been seen occurring 300 years ago, from Earth. As more matter piles up near the black hole, the X-ray output becomes greater. When gas spirals inward toward the black hole, it heats up to millions of degrees and emits X-rays. The observations, collected between 19, revealed that clouds of gas near the central black hole brightened and faded quickly in X-ray light as they responded to X-ray pulses emanating from just outside the black hole. Perhaps it’s just resting after a major outburst." "But now we realise that the black hole was far more active in the past. "We have wondered why the Milky Way’s black hole appears to be a slumbering giant," says team leader Tatsuya Inui of Kyoto University in Japan. Yet the energy radiated from its surroundings is thousands of millions of times weaker than the radiation emitted from central black holes in other galaxies. The finding helps resolve a long-standing mystery: why is the Milky Way’s black hole so quiescent? The black hole, known as Sagittarius A-star (A*), is a certified monster, containing about 4 million times the mass of our Sun.
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