This garden universe vibrates complete
Some, we get a sound so sweet
Vibrations reach on up to become light
And then through gamma, out of sight
Between the eyes and ears there lie
The sounds of colour and the light of a sigh
And to hear the sun, what a thing to believe
But it’s all around if we could but perceive
To know ultra-violet, infra-red, and x-rays
Beauty to find in so many ways.
Imagine looking up at the night sky and seeing not only the stars, planets even the auroas but hearing them too. Down here on Earth, we are used to seeing and hearing things, but we don’t hear the sun our nearest star but if our eyes were sensitive to the pressure waves occurring in the sun then we could see the sound, almost a type of synaesthesia.
Now that some of you out there will be quoting the tagline from Alien, “in space no one can hear you scream” and that its true but there are exceptions where there is sound in space but more on that later.
What we define as sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. We hear this movement with our ears and our eyes pick up electromagnetic waves at very high frequencies, far, far, higher than the frequency of sound which we can hear.
But if you take those electromagnetic waves and sonify them, then you too can hear the universe.
This is a video I was going to do a few years back but it just put on the back burner until a couple of weeks back when I happened upon a project run by NASA called HARP and no this is not the HAARP atmospheric heating project I have spoken about before this is the Heliophysics Audified: Resonances in Plasmas project, or H.A.R.P. which I will come on the later but indirectly hearing what goes on in space is a lot more common than you might think.
Back before digital TV’s and radio, the signals sent by the broadcasters were analog and if you unplugged the TV ariel or tuned to a spot in between the stations, you would see random snow or the moving ants effect on the TV and on a radio a hissing crackling sound.
Well, part of that sound and images comes from the CMB or the Cosmic Microwave background radiation. This is the oldest light in the universe which was emitted just after the Big Bang when electrons and protons that formed the plasma recombined to form the first hydrogen atoms as the temperature cooled to around 3000 K when the universe was approximately 379,000 years old.
Since then, and over 13.8 billion years, this light has been stretched by the expansion of space so much it is now in the radio spectrum and can be picked up by our electronic equipment like tv’s and radios. But this is not the only the signals we pick up from space, anything that interacts with or emits charged particles, X and gamma rays makes signals that can be picked up.
Pulsars are another phenomenon that was originally mistaken for extra-terrestrial signals. Pulsars are neutron stars, super dense remnants of once very large stars that have run out of fuel and gravity has taken over to produce a supernova.
During the star’s collapse, the crush is so great that the electrons and protons combine to create neutrons and go from multiple times the size of our sun to something that is about 20km across and become the densest objects in the known universe outside of a black hole.
These stars just didn’t have the mass to go beyond the neutron star stage and become black holes. A 1cm cube of this material would weigh about 1 billion tons here on Earth, it would take an 800-meter cube of the Earth’s crust to weigh the same.
Most of these neutron stars just go cold and produce X-rays but some inherit the magnetic field from when they were giant stars and as the star collapses their rotational speed increases and in the fastest found so far, they do a complete rotation 716 times per second.
Their intense magnetic fields focus particles into incredibly powerful beams which we hear as regular clicks or pulses but with the fastest ones like PSR J1748−2446ad at 614 rotations per second, it sounds like an audible tone at the musical note D#5.
Now when its said that there is no sound in space, it’s because space is normally a vacuum and so there is no medium like gas for sound to travel through. But in some places like a galaxy cluster, there is so much gas and plasma true sound or pressure waves can propagate through it.
This was discovered in 2003 by the Chandra X-ray telescope but it has never been processed to bring it in the range of the human ear.
This process known as sonification converts data from things like images or radio data into the range of human hearing. The purpose is to allow us to hear the data. We humans are listening to patterns in sound all the time, in speech, music, and the natural world and we are very good at picking these up and filtering out interesting sounds even among a great deal of noise, just like you can hear a conversation in a room full people, so hearing data from extraterrestrial sources gives us another way to analyze it.
One of the earliest and most successful application types of sonification is the Geiger counter, which turns the detection of ionizing particles or X and Gamma rays depending on the type of detection tubes used which we cannot see or feel into audible clicks, the more the clicks, the more dangerous it is for humans, a sound that has become synonymous with radiation.
Data from the Chandra X-ray telescope showed that there were pressure waves being created in the gas surrounding the black hole at the center of the Perseus galaxy cluster as the material was being drawn into it. However, due to the huge scale of the phenomenon, their frequency was 57 octaves below a middle C on a piano.
If you are unfamiliar with octave scales, each octave up doubles in frequency, and each octave down halves in frequency. To bring out the original sounds from the Chandra data, meant that it had to be increased in frequency by 57 to 58 octaves or by 144 to 288 million billion times the original frequency.
The sound waves were extracted in radial directions, that is, outwards from the center and then scaled up. The radar-like scan allows you the hear the sound that was emitted in different directions and the blues and purples of the image were both x-ray data.
So how does sonification work?. Well, there are various ways to hear an image but one way is to break the light spectrum into three parts, infrared, visible light and X-rays and then resynthesize the sound and apply that to the light bands as either low sounds, medium sounds or high sounds. Some even use musical instrument sounds and play them with the data to create orchestral soundscapes.
The data that makes up this image of M16 or “The pillars of creation” is scanned left to right and as the scan point traverses the image the synthesized sound for each of the bands is mixed together to create a sonic image.
These methods change depending on what is being scanned. The gravitational waves that the LIGO experiment detected from the collision of two black holes 1.4 billion years have been sonified so we can hear the gravity waves as they traveled through the solar system and the earth, stretching and squeezing the fabric of spacetime itself.
The LIGO equipment uses two laser beams at right angles to each other and an Interferometer. The laser light is split and then sent along each of the 4km long arms to a mirror at the end of each where it is then reflected back and recombined. If the is any difference in the length of the arms the returned beams will be out phase and this difference will be picked up by the Interferometer.
This is so sensitive it can measure changes in distance as small as 1000th the diameter of a proton that makes up the nucleus of an atom. Now with the sonification of the data, we can hear the changes as the gravity waves passed through the earth changing the length of the arms as well.
Of course, some will say that this is not hearing the real thing but there is no way that we can even see infrared and x-rays let alone gravity waves, this is just a proxy method that allows us to do that.
Just as in the amazing multicolor pictures we see of galaxies and nebula, they are a man-made assembly of the different light spectra in one image.
And this brings us to the HARP project. This is a NASA citizen science project to analyse the data captured from the THEMIS mission which was launched in 2007 to understand what created the northern and southern lights or aurora and how the solar wind and solar storms interact with the earth’s magnetic field to create substorms, the magnetic equivalent to severe weather down on the surface.
When solar plasma hits the earth’s magnetic field it vibrates like the strings on a harp but its at a very low frequency, so it is processed to bring it up to our human hearing range. Being a citizen science project, you can then take part in the study using a web-based tool called HARP to listen to the data and just report back what you hear. Part of this is to see if studying space sounds with your ears is as reliable as using traditional computer analysis.
Sonification is a relatively new way of experiencing how the sun affects the earth and what goes on in space both in our solar system and across the universe, wherever we can gather data from and turn it into sound and looks to add a new and exciting sonic dimension to astronomy.
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