Space is not silent. At least not if you know how to listen. The Voyager I spacecraft has now departed our solar system, and as it flies through interstellar space, it’s detecting the steady drone of plasma waves. Like the hum of fluorescent bulbs, this hum comes from excited atoms. In this case, the gas is super low density and extends at least 10 AU. This hum is in addition to the loud bursts associated with solar activity exciting the gas and seems to be caused by thermal processes or quasi-thermal noise. These new results are published in Nature Astronomy by a team led by Stella Koch and show that even middle-aged spacecraft have good science they can do.

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Cornell University press release

“Persistent plasma waves in interstellar space detected by Voyager 1,” Stella Koch Ocker et al., 2021 May 10, Nature Astronomy