NASA's Voyager-1 spacecraft, travelling outside the solar system, has sent back new data revealing a 'hum' given off by interstellar gas 14 billion miles from the Earth. The Interstellar Medium fills interstellar space and blends smoothly into the surrounding intergalactic space. Through stellar winds and supernovae the stars replenish the matter in the interstellar medium. Crossing into interstellar space involved going through the heliopause - the theoretical boundary where the Sun's solar wind meets the interstellar medium. Now we know we don't need a fortuitous event related to the sun to measure interstellar plasma.

Source: Daily Mail May 10, 2021 15:03 UTC