In this video we play a song as if we were increasing the number of telescopes in the EHT, essentially fixing the broken piano keys.

To make this a bit more clear, listen to the video below (use headphones for the best experience). Although hearing a song this way is definitely not perfect, often times there is still enough information to follow along. However, as we only have telescopes at a few locations, we must recognize the song being played with just a few notes. If we had telescopes located everywhere on the globe we would be able to hear all possible notes, and thus hear a perfect rendition of the song. Watching the black hole with the EHT is a bit like listening to a song that is played on a piano that has a lot of broken keys. The tone that is heard is related to the projected distance between the telescopes, as seen from the direction of the black hole the farther apart the telescopes, the higher the pitch of the note. Each pair of telescopes produces a measurement that corresponds to the tone of a just a single note. To give you an idea of how this works, you can think about the measurements we make from telescopes in the EHT as a bit like notes in a song. Since there is a lot of missing data, you may ask how making a picture is even possible. The imaging algorithms we develop fill in the gaps of data we are missing in order to reconstruct a picture of the black hole. However, since we are only collecting light at a few telescope locations, we are still missing some information about the black hole’s image. The light we collect gives us some indication of the structure of the black hole. Once the EHT has measured data from the black hole, we still need to make a picture from it - a process referred to as imaging. The Event Horizon Telescope (EHT) collects light from the black hole using a small number of telescopes distributed around the Earth. How do we make a picture from the sparse data collected by the EHT?

Telescopes auditory illusions