A Universe of Sound

Every sound begins with a vibration. When those vibrations travel through the air, they can enter the human eardrum where they are eventually turned into electrical signals that our brain interprets as sound. These vibrations can come from many sources here on Earth as well as those in our Solar System and even across our Universe.

Sound travels in a wave and has its own distinct properties. One of these is frequency, which is the measurement of how many peaks (or troughs) of a wave pass a particular point over a certain period of time. Frequency is most often measured in the unit of the Hertz (Hz), which is the number per second. In general, humans can hear in the range of 20 to 20,000 Hz. An elephant can hear in the range below humans, while dogs and cats are sensitive to much higher-frequency sounds.

Beyond the animal world, sounds can come from a variety of sources. Natural phenomena such as weather, earthquakes, and even black holes can produce very low-frequency sounds, while humans have harnessed sound for improvements in technology such as medical imaging.

Here we will explore how scientists are using NASA's Chandra X-ray Observatory and other instruments around the world and in space to study the cosmos through sound. Whether it comes from vocal chords in our throats or the surface of the Sun, sound plays a valuable role in our understanding of the world and cosmos around us.


Perseus galaxy

A Black Hole Sings.
Perseus Cluster: a galaxy cluster about 250 million light years from earth.

Chandra’s 53-hour observation of the central region of the Perseus galaxy cluster has revealed wavelike features that appear to be sound waves. The features were discovered by using a special image-processing technique to bring out subtle changes in brightness. These sound waves are thought to have been generated by explosive events occurring around a supermassive black hole in Perseus A, the huge galaxy at the center of the cluster. The data also shows two vast, bubble-shaped cavities filled with high-energy particles and magnetic fields. These cavities create the sound waves by pushing the hot X-ray emitting gas aside. The pitch of the sound waves translates into the note of B flat, 57 octaves below middle-C. This frequency is over a million billion times deeper than the limits of human hearing.

More on this result.


EX Hydrae

This artist's conception shows the binary star system EX Hydrae, which consists of a normal star (right) and a white dwarf (left, at center of disk). Known as a cataclysmic variable, EX Hydrae fluctuates in X-ray brightness as the white dwarf consumes gas from its companion. Illustration: Christine Pulliam (CfA) (CfA)

Blues-style Hydra: Credit: G.Sonnert
More styles and variations of this "star song"
Read the full story and listen to all of the results on Sonnert's Star Songs website.

Star Songs: Converting Data into Sound and Music

Gerhard Sonnert, a research associate at the Center for Astrophysics | Harvard & Smithsonian, worked with Wanda Diaz-Merced, an astronomer/computer scientist whose blindness led her into the field of sonification (turning astrophysical data into sound), as well as Volkmar Studtrucker, a composer, to turn astrophysics data sonification into music.

Diaz-Merced lost her sight in her early 20s while studying physics, and now regularly works with software that can help present numerical data as sound, using pitch, volume, or rhythm to distinguish between different data values. Diaz-Merced has used NASA's Chandra X-ray Observatory of a source called EX Hydrae - a binary system consisting of a normal star and a white dwarf. Known as a cataclysmic variable, it fluctuates in X-ray brightness as the white dwarf consumes gas from its companion.

Diaz-Merced programmed the Chandra X-ray data into special software and converted it into sound. Sonnert then sensed that the notes could become something more harmonious to the ear. He contacted Studtrucker who chose short passages from the sonified notes, about 70 bars in total, and added harmonies in different musical styles. Sound files that began as atonal compositions transformed into blues jams and jazz ballads, to name just two examples of the nine songs produced.

The project shows that something as far away and otherworldly as an X-ray-emitting cataclysmic variable binary star system can be significant to humans for two distinct reasons - one scientific and one artistic.


Sound demonstration of Crab vs other pulsars:

Crab Nebula

Pulsar sounds credit: © 2014, W. Christian and F. Esquembre

More information

Listen to a Pulsar Clock

Turning a pulsar's rotational data into sound makes it easier to observe patterns and make comparisons between different nebulous pulsar rotational speeds. as a pulsar ages it spins at a slower speed. listen to the different pulsar heartbeats. what can you guess about how fast these different pulsars rotate? Which pulsar is the oldest? How about the youngest?

Neutron stars are strange and fascinating objects. They represent an extreme state of matter that physicists are eager to know more about. Yet, even if you could visit one, you would be well-advised to turn down the offer.

The intense gravitational field would pull your spacecraft to pieces before it reached the surface. The magnetic fields around neutron stars are also extremely strong. Magnetic forces squeeze the atoms into the shape of cigars. Even if your spacecraft prudently stayed a few thousand miles above the surface neutron star so as to avoid the problems of intense gravitational and magnetic fields, you would still face another potentially fatal hazard.

If the neutron star is rotating rapidly, as most young neutron stars are, the strong magnetic fields combined with rapid rotation create an awesome generator that can produce electric potential differences of quadrillions of volts. Such voltages, which are 30 million times greater than those of lightning bolts, create deadly blizzards of high-energy particles.

These high-energy particles produce beams of radiation from radio through gamma-ray energies. Like a rotating lighthouse beam, the radiation can be observed as a pulsing source of radiation, or pulsar. Pulsars were first observed by radio astronomers in 1967. The pulsar in the Crab Nebula, one of the youngest and most energetic pulsars known, has been observed to pulse in almost every wavelength—radio, optical, X-ray, and gamma-ray.



Galaxy Center

Galactic Center

Cassiopeia A

M16/Pillars of Creation

Galactic Center Sonification

The center of our Milky Way galaxy is too distant for us to visit in person, but we can still explore it. Telescopes gives us a chance to see what the Galactic Center looks like in different types of light. By translating the inherently digital data (in the form ones and zeroes) captured by telescopes in space into images, astronomers create visual representations that would otherwise be invisible to us.

But what about experiencing these data in other senses like hearing? Sonification is the process that translates data into sound, and a new project brings the center of the Milky Way to listeners for the first time. The translation begins on the left side of the image and moves to the right, with the sounds representing the position and brightness of the sources. The light of objects located towards the top of the image are heard as higher pitches while the intensity of the light controls the volume. Stars and compact sources are converted to individual notes while extended clouds of gas and dust produce an evolving drone. The crescendo happens when we reach the bright region to the lower right of the image. This is where the 4-million-solar-mass supermassive black hole at the center of the Galaxy, known as Sagittarius A*, resides, and where the clouds of gas and dust are the brightest.

Users can listen to data from this region, roughly 400 light years across, either as “solos” from NASA’s Chandra X-ray Observatory, Hubble Space Telescope, and Spitzer Space Telescope, or together as an ensemble in which each telescope plays a different instrument. Each image reveals different phenomena happening in this region about 26,000 light years from Earth. The Hubble image outlines energetic regions where stars are being born, while Spitzer’s infrared data show glowing clouds of dust containing complex structures. X-rays from Chandra reveal gas heated to millions of degrees from stellar explosions and outflows from Sagittarius A*.

Galactic Center

Galaxy Center X-ray





Sounds from Around the Milky Way

Cassiopeia A Sonification

This sonified piece is of the remains of a supernova called Cassiopeia A, or Cas A. In Cas A, the sounds are mapped to four elements found in the debris from the exploded star as well as other high-energy data. The distribution of silicon, sulfur, calcium, and iron are revealed moving outward from the center of the remnant, starting from the location of the neutron star, in four different directions, with intensity again controlling the volume. There is also a fifth audio path moving along the upper left jet.

Cassiopeia A








Sounds from Around the Milky Way

M16/Pillars of Creation Sonification

In the “Pillars of Creation” piece, the sounds are generated by moving horizontally across the image from left to right as seen in both optical and X-ray light. As with the sonification of the Galactic Center, the vertical position of the recorded light controls the pitch, but in this case it varies over a continuous range of pitches. Particular attention is paid to the structure of the pillars which can be heard as sweeps from low to high pitches and back. The two different "melodies" of optical and X-ray light can be enjoyed individually or simultaneously.

The Eagle Nebula (M16)




Sounds from Around the Milky Way

This sonification of the Galactic Center, Cas A, and M16 was led by the Chandra X-ray Center (CXC) as part of the NASA's Universe of Learning (UoL) program. The collaboration was driven by visualization scientist Kimberly Arcand (CXC), astrophysicist Matt Russo and musician Andrew Santaguida (both of the SYSTEMS Sound project.)

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Additional support from NASA's Universe of Learning (UoL). UoL materials are based upon work supported by NASA under award number NNX16AC65A to the Space
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