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The Lowest Note in the Universe
November 2003
Picture a piano keyboard. The farther to the left your hand goes, the lower the note being played. The bottom key isn't the lowest note there is, though. A double-bass in a symphony orchestra could play a note lower than that. And a synthesizer could play a lower note than a double-bass. Beyond that, there are pitches so low that we can't even hear them--they are beneath the relatively small range of frequencies the human ear can pick up. But just because we can't hear such low frequencies doesn't mean they don't exist, any more than pitches that are too high for us. Just ask a dog!
The Note No One Knew Was There
Just recently, a team of scientists in England accidentally ran across a note so unbelievably low that it set a new record--one unlikely to be broken any time soon. What kind of scientists were they? Not acoustical engineers, not recording technicians, but astronomers. The lowest note in the universe is being generated by a black hole.
The astronomers even know what note it
is in particular: it's a B flat. Only this B flat is about
fifty-seven octaves below the one you find in the middle of
a piano. Think of it this way: you can hear Middle C by playing
the key that is right in the center of a keyboard; move down
twelve keys to hear the same note one octave lower. Now, imagine
being able to do that fifty-six more times. That super-low
note, many millions of times lower than any animal's ear could
register, is occurring out there in space. Way out
there--the musical black hole is a good 250 million light
years away.
A Singing Black Hole?
A black hole is the remains of a star that has used up most of its nuclear fuel, run through the course of its life, and collapsed under its own gravitational weight. When a black hole forms, it creates a region in space into which anything nearby will be drawn, including light itself. That's why black holes are black.
This particular black hole is at the center
of a galactic cluster called the Perseus cluster. A “galactic
cluster” is just what it sounds like--many galaxies
all huddled together, comprising billions of stars, along
with a big cloud of interstellar gas.
The black hole itself only pulls things
in, but because it is so powerful, all sorts of effects happen
to nearby matter as it is violently hauled down. One result
is that huge numbers of particles are actually fired away
from the region of the hole in titanic jets. These jets crash
into the gas cloud that surrounds the hole and cause a series
of pressure waves to ripple outward, much like the way water
in a pond ripples out from the spot where someone has leapt
in. Pressure waves traveling through any medium are what constitutes
sound. And, if the waves have a particular frequency, we call
it a note. As unlikely as it seems, the entire Perseus cluster
is reverberating like a plucked string.
Imagine This: A Galactic Symphony
Astronomers at the university of Cambridge
in England who discovered the distant B flat now speculate
that many galactic clusters, and even individual galaxies,
could be generating ultra-low pitches in this way. If they’re
right, it will help explain how galaxies form, why they have
the temperatures they do, and more. To us humans, the idea
of an entire galactic cluster acting like a musical instrument
is bizarre and somehow charming. More than that, though, the
energy released by the steadily out-going pressure waves may
be a significant component in the structure and functioning
of these enormous systems.
Activity
Find a piano and have someone show
you where B flat is. Then, with your eyes closed, listen to
the notes each key makes while moving downward, one key at
a time. Can you tell when you have come to another B flat,
one octave lower?
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