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Caption: You can measure a black hole’s mass by its echoes. You know how you can estimate how far away a storm is by counting the seconds between lightning and thunder?… more You can measure a black hole’s mass by its echoes. You know how you can estimate how far away a storm is by counting the seconds between lightning and thunder? Astronomers use the same basic idea to study supermassive black holes – using light instead of sound. Around a black hole sits a swirling accretion disk, constantly flickering and flaring. That flickering light travels outward and “echoes” off the surrounding gas clouds. Because light takes time to travel, those echoes arrive with a delay. By measuring that delay – using a technique called reverberation mapping – astronomers can calculate the size of the system, like using echoes as a cosmic ruler. But size alone isn’t enough. To measure how massive the black hole is, scientists also measure how fast the gas is moving using Doppler broadening – the same principle that makes a passing siren sound higher-pitched as it approaches and lower as it moves away. Put those two pieces together, the size from echoes and the speed from Doppler shifts and suddenly… you can weigh something from millions of light years away. Black holes may not shine – but their echoes are helping us understand how the universe built its biggest monsters. #BlackHoles #Astrophysics #Astronomy #Space #Physics less
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