The Sound of a Fermi Gamma-ray Burst

What does the universe look like at high energies? Thanks to the FermiLarge Area Telescope (LAT), we can extend our sense of sight to “see”the universe in gamma rays. But humans not only have a sense of sight,we also have a sense of sound. If we could listen to the high-energyuniverse, what would we hear? What does the universe sound like?

A gamma-ray burst, the most energetic explosions in the universe, converted to music. Made by Sylvia Zhu (music) and Judy Racusin (animation)

Every photon has its own energy and frequency; the higher the energy, the higher the frequency. Some photons have just the right frequencies for us to see them as different colors, while others — such as the gamma rays studied by the Fermi LAT — are much too energetic to be seen with our eyes. Sound waves have frequencies too, and similarly, we can hear some of them as musical notes. So what happens if we convert high-energy photons into musical notes?

Gamma-ray bursts (GRBs) are some of the most powerful explosions in the universe. GRB 080916C was a particularly energetic burst that occurred in September of 2008. The brightest part of it lasted less than a minute, during which the LAT detected hundreds of gamma rays from the extremely-distant explosion; when we converted the data to music, we slowed the rates down by a factor of five times to hear the individual gamma rays better.

In translating the gamma-ray measurements into musical notes we assigned the photons to be “played” by different instruments (harp, cello, or piano) based on the probabilities that they came from the burst. This particular conversion is a fairly simple one; We built this on work done by other members of the LAT team (Luca Baldini and Alex Drlica-Wagner) who explored converting our data into music in different ways.

In the beginning of the song, before the burst starts, the harp plucks out a few lonely notes. After about half a minute, the piano joins in on top of the harp background, and the notes begin to pile on more and more rapidly. The cello enters the scene as the burst begins in earnest.

We created an accompanying animation to help see what is happening. The top panel shows each individual gamma-ray. The colors refer to low (red), medium (blue) and high (green) quality gamma-rays (played by harp, cello and piano respectively). The energy of the gamma-ray is on the y-axis (higher energy gamma-rays are towards the top of the plot) and the arrival time of the gamma-rays are on the x-axis (later arriving gamma-rays are further to the right). The vertical white line tells you where the music is currently playing. The bottom panel shows the number of gamma-rays (which is the number of notes played) in each time slice.

By converting gamma rays into musical notes, we have a new way of representing the data and listening to the universe.

Happy Birthday Fermi

The cake features a (hand drawn) Fermi gamma-ray skymap, showing the bright bandproduced by diffuse emission from the disk of our Galaxy, the Fermibubbles (in black) – huge lobes of gamma-rays extending above and below theGalactic disk, and many point sources of gamma-rays (active galaxies,pulsars and much more).

The Fermi observatory, sculpted here from fondant, shows the Large AreaTelescope (grey box) and a 3-d representation of the NaI (black/yellow)and BGO (orange) detectors of the gamma-ray burst monitor. Combinedthese instruments provide observations over an extraordinarily largeswath of the electromagnetic spectrum (from 8keV to over 300 GeV).

A pen is included to show the scale – this was a monstrous cake! The 70 or soof us at the launch anniversary celebration only got through half thecake, despite being a delicious combination of chocolate and vanilla. This is fortunate for our waistlines given the followingingredient list:
7 lbs flour
9 lbs sugar
30 eggs
6 lbs butter
3 lbs marshmallow
1 lb corn starch
8 cups of buttermilk