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Geek Trivia: Low and behold

What celestial object emits the lowest frequency note ever detected?

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According to scientists, Julie Andrews was right: The hills are alive with the sound of music. Okay, so maybe music is a generous term for the phenomenon, but the hills really are making noise, as is the entire planet Earth. You just can't hear it because the Earth's natural hum is subsonic, occurring at a frequency far below the range of the human ear.

Scientists first discovered the Earth's hum—technically referred to as background-free oscillation—while sorting through seismic data. They couldn't attribute a significant percentage of this "ground sound" to recognized seismic activity, meaning that the Earth itself wasn't moving—something was moving the Earth.

Seismologists eventually realized that the atmosphere was actually pushing and pulling against the planet, creating subsonic noise beyond the normal rumble of seismic activity. Put simply, the air is "playing" the planet like an instrument, creating a distinct hum.

The hum changes throughout the course of the year, suggesting a seasonal and therefore thermal origin of the atmospheric pressures fueling the Earth's hum. As the changing seasons heat and cool the air, the atmosphere expands and contracts accordingly, changing the placement and intensity of pressure exerted against the earth, resulting in a change in volume of the Earth's hum.

Given the parameters of this phenomenon, it's very likely that the other planets in the solar system possessing an atmosphere also have unique, cyclical hums. As such, Mars and Venus are probable candidates for planetary hums.

If it's true, that means a cosmic symphony of planetary tones is playing in our solar system even as we speak. We just can't hear it because the oscillations are simply too low in frequency.

Still, don't think that the planets have the market cornered on low-frequency sound. In 2003, scientists discovered that a nonplanetary celestial object was emitting the lowest-frequency note ever detected.


What celestial object emits the lowest frequency note ever detected, far below the low-frequency hum produced by Earth?

A black hole at the center of a galaxy in the Perseus Cluster is currently generating a deep B-flat note that's 57 octaves below a tuned middle C on a piano.

Put another way, the lowest frequency sound a human being can detect is 0.05 hertz, or a frequency of one-twentieth of a second. The Perseus Cluster black hole generates sound with a frequency of 10 million years. This represents the most sub-bass frequency ever detected.

To be precise, the black hole itself is silent, but the stellar gases pulled into the gravitational well of the black hole are not. As the gas falls toward the black hole's event horizon, it accelerates to velocities approaching the speed of light. This acceleration creates turbulence, which in turn generates light, heat, and, within the medium of the gas, sound.

Of course, space being a near total vacuum (and the black hole being 250 million light years away), the sound of the black hole hasn't actually reached Earth. British astronomers discovered it using NASA's Chandra X-ray Observatory while trying to analyze the formation of galactic clusters such as Perseus.

The black hole in question is unusually energetic, emitting a significant amount of X-ray radiation, which scientists used to model the thermal and kinetic activity of the matter pulled into the black hole.

This modeling revealed the sonic tone induced by the black hole, which could help explain why galactic gas clusters stay warm, rather than cooling and collapsing. Massive celestial objects such as black holes are "ringing" the gas clusters, which keep them energized and hot, leading to some of the specific star formation behavior that scientists had previously been unable to explain. Now that sounds like some great Geek Trivia.

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The Quibble of the Week

If you uncover a questionable fact or debatable aspect of this week's Geek Trivia, just post it in the discussion area of the article. Every week, yours truly will choose the best post from the assembled masses and discuss it in the next edition of Geek Trivia.

This week, TechRepublic member Shchors has a quibble with the Sept. 8 edition of Geek Trivia, "A date with destiny."

"You say that Harvard University was the 'first institute of higher learning in the New World.' Harvard was the first college in [North] America (the continent), but there were a few universities before it was founded in 1636.

"The first university of America, which continues to exist today, is the National Autonomous University of Mexico, founded in 1551, although there's some debate on whether the University of Michoacan (also in Mexico) was founded before that year."

Exhibiting typical American egocentrism, I used the terms American colonies and New World interchangeably, and this reader was right to call me out on it. Thanks for keeping me honest, reader.

The Trivia Geek, also known as Jay Garmon, is a former advertising copywriter and Web developer who's duped TechRepublic into underwriting his affinity for movies, sci-fi, comic books, technology, and all things geekish or subcultural.

About Jay Garmon

Jay Garmon has a vast and terrifying knowledge of all things obscure, obtuse, and irrelevant. One day, he hopes to write science fiction, but for now he'll settle for something stranger — amusing and abusing IT pros. Read his full profile. You can a...

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