In April of 2019, the first picture of a black hole appeared on the internet. But how could we have taken a picture of an object far, far away from us in space, that does not let light escape its horizon?
Scientists’ solution was to image the black hole’s silhouette against its glowing background rather than the black hole itself. But there was still the looming issue of imaging something as far away as a black hole, in this case, supermassive black hole M87*, which is 53 million lightyears away, or approximately 320 quintillion miles from Earth.
Intuitively, the first thought would be to have one gigantic telescope to look in the depths of space and focus in on one mini point. This is because the strength of the telescope depends on its diameter–the longer the diameter, the higher the resolution will be. But building a big telescope as big as the Earth would be very hard to accomplish. Instead, the team working on the Event Horizon Telescope, or EHT, devised a plan to use a collection of telescopes instead to record the event and stitch the individual images together. This way, the diameter of the collective telescope will be as long as the distance between the two farthest telescopes, which in this case between telescopes at the South Pole and in Spain, which is almost the diameter of Earth. This technique is called Very Long Baseline Interferometry, or VLBI.
Other challenges included synchronizing all of the data being received by the telescopes in the collection, and counting on clear weather so that all of the telescopes could see during the recording time. During the 10 days that the telescopes were recording data, for 4 of the days all 8 of the telescope sites had clear weather, which allowed for clear image processing. For synchronizing all of the data, each telescope used the same atomic clock locked into GPS time standard, and their maximum deviation could only be up to a fraction of a millimeter. Since there was so much information being recorded throughout the 5 days, the complete data amounted to more than 5 petabytes. In comparison, our phones usually have between 32 GB to 512 GB of storage. That means that the amount of data that was analyzed was over a billion bytes more than the storage on our phones, which we can use over the course of many years.
This picture of the black hole allowed scientists to more directly calculate the mass of black holes and confirm the real image to what general relativity predicts. It also helped scientists test their hypotheses about the structure of black holes, such as the emission of jet particles and the formation of accretion disks. This was a feat that truly revolutionized the field of astrophysics.
You may have also heard of the name Katie Bouman in association with the black hole. Katie Bouman was an MIT graduate student when she helped develop algorithms in order to complete the incredibly complex and large calculations required to stitch the images from the different telescopes together into one cohesive picture. She is a champion of women in STEM and serves as an inspiration to other females interested in the fields of science, technology, and innovation.