We don’t often think of the universe as noisy. In fact, most of us tend to imagine it’s dark and eerily quiet. Well, it is. But it is also abuzz with the subsonic hum of billions of black holes. And NASA is helping us hear what these mysterious objects sound like.
Because the vast expanse of space is mostly vacuum, you might rightly deduce that there’s no medium for sound waves (reverberations of matter). While that’s true, astronomers have noticed that galaxy clusters have enough stuff – gas, dust and particles – to transfer sound.
Just in time for the organisation’s Black Hole Week (last week), NASA released a new “sonification” of the supermassive black hole at the centre of the Perseus galaxy cluster. The cluster contains more than 1000 galaxies and is about 240 million lightyears from Earth.
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Perseus’ hum has been studied by astronomers since 2003. The ripples that the black hole in its centre causes can be translated into a note 57 octaves lower than middle C. And, yes, before you ask, that’s quite a bit lower than the late bass-baritone crooner Barry White could sing.
This new sonification of Perseus is the first time the previously identified sound waves have been made audible. But first they had to be transposed into the range of human hearing. They were scaled up by 57 and 58 octaves. To put that another way, the sound’s frequency was made 144 and 288 quadrillion – 1 with 15 zeroes – times higher than the original wave. The sound waves imaged by NASA’s Chandra X-ray Observatory are seen in the video of Perseus’ music below.
NASA also released another new sonification last week. The famous Messier 87 (M87) black hole has been studied for decades and hit headlines in 2019 as part of the data from the Event Horizon Telescope project. The sonification uses X-ray data from Chandra, optical light from NASA’s Hubble Space Telescope and radio waves from the Atacama Large Millimeter Array in Chile. M87’s song was then produced by mapping the three different radiation ranges to different audible tone ranges.
The projects are part of a broad endeavour to “sonify” the universe. The attempts to hear the symphony of space are fun, but also tells us about the physical phenomena which cause these ripples.
Black holes are extremely dense, massive objects. Their gravitational pull is so strong that not even light can escape once it passes the “event horizon”. Near the black hole, the theory of general relativity proposed by Einstein is in overdrive. “I just love that we can ‘hear’ the general relativity in these simulations,” the leader of a Massachusetts Institute of Technology sonification project, astrophysicist Dr Erin Kara, told the New York Times.
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