NASA Voyager 1 Has Detected A Mysterious Cosmic 'Hum' In Deep Space

The Voyager 1 spacecraft is detecting the background "hum" of interstellar space at a low frequency of 3kHz for the first time 44 years after it was launched from Earth.

The Voyager 1 spacecraft, launched in September 1977, is now approximately 14.1 billion miles (22.7 billion km) from Earth — nearly 152 times the distance between our planet and the sun — and is still collecting and transmitting data.

After visiting the massive planets Jupiter and Saturn decades ago, Voyager 1 is now providing insight into interstellar space, and has spent more than four decades traveling deep into space, and is now the most distant human-made object in the universe.

According to scientists, the discovery, published in the journal Nature Astronomy, provides a unique and never-before-seen glimpse of the interstellar environment — the frontier beyond the reaches of our cosmic neighborhood's sun and planets.

"Voyager 1 is in an interesting region of space that is outside this thing called the heliosphere, which is the protective bubble that encases all the planets in the solar system,"  a Cornell University doctoral student in astronomy and lead author of the study. "So, it's really our only tool for directly sampling the nature of interstellar space."

The faint but constant vibrations detected by the Voyager 1 essentially represent the background noise that can be found in the vast space between star systems. These vibrations, known as persistent plasma waves, were detected at radio frequencies with a narrow bandwidth during Voyager 1's three-year journey through interstellar space.

The vast spaces between star systems in a galaxy are not completely vacuumed. The interstellar medium is a mixture of matter and radiation found at low densities, mostly gas. This interstellar gas, dust, and energetic particles like cosmic rays make up about 15% of the visible matter in our Milky Way galaxy.

Much of the interstellar medium is in a state known as plasma, ionized or electrically charged. And Research suggests that when the sun occasionally emits a burst of energy known as a coronal mass ejection, which disrupts this medium and causes the plasma, or ionized gas, of interstellar space to vibrate. 

These vibrations are beneficial because they allow astronomers to measure the density of the plasma — the frequency of the waves through the plasma can reveal how close the ionized gas molecules are together.

"The persistent plasma waves that we've just discovered are far too weak to actually hear with the human ear. If we could hear it, it would sound like a single steady note, playing constantly but changing very slightly over time," said Ocker.

Ocker also said, "Interstellar plasma is extremely diffuse compared to what we're used to on Earth. In this plasma, there are about 0.1 atoms for every cubic centimeter, whereas the air we breathe on Earth has billions of atoms for every cubic centimeter." 

The new findings suggest that by tracking these persistent vibrations in the interstellar medium, it may be possible to elicit specific properties of this environment, such as its density. This, in turn, will help astronomers better understand the mysterious environment beyond the solar system — as Voyager 1 travels further and further away from Earth.