The “wow element", as MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) tweeted on 10 April, lies in the fact that “...imaging a black hole with one telescope would require it to be almost as large as Earth itself".
Black holes are extraordinary cosmic objects with enormous masses, but extremely compact sizes. Researchers always wanted to see an image of one to investigate the extreme warping of space-time that black holes cause. But the distance of the black holes from the earth poses a very big difficulty when trying to photograph it.
The photographed black hole, for instance, is 500 million trillion km away from Earth. It is gigantic—40 billion km across, which is three million times the size of our planet, and has been described by scientists as “a monster".
As Bouman herself explained three years ago, that since a black hole is “very, very far away and very compact", “...to image something this small means that we would need a telescope with a 10,000-kilometer diameter, which is not practical, because the diameter of the Earth is not even 13,000 kilometers".
Because of their long wavelengths, radio waves require large antenna dishes, but the largest single radio-telescope dish in the world has a diameter of just 1,000 ft, which would be unable to take sharp images of even the moon, let alone a black hole.
To address this issue, scientists used multiple telescopes and merged their results using the special algorithm created by Bouman.
The Event Horizon Telescope (EHT) is not a single device. It operates a planet-scale array of eight ground-based radio telescopes that are linked together. The Black Hole Cam (BHC) Team, led by astrophysicists from Goethe University in Frankfurt, the Max-Planck Institute for Radio Astronomy in Bonn and the Radboud University in Nijmegen, the Netherlands, are part of this collaboration.
Bouman is a postdoctoral fellow with ETH and an assistant professor in the CMS department at Caltech.
The focus of her research is on using emerging computational methods to push the boundaries of interdisciplinary imaging. She developed the algorithm with the help of researchers from MIT CSAIL, the Harvard-Smithsonian Center for Astrophysics, and the MIT Haystack Observatory.
The aim was to combine data collected from radio telescopes scattered around the globe, under the auspices of the EHT. The project essentially sought to turn the entire planet into a large radio telescope dish.
When Bouman and her team developed the algorithm, she christened it CHIRP, which stands for Continuous High-resolution Image Reconstruction using Patch priors. The “clever algebraic solution", as explained in a 6 June 2016 note by MIT, was used to make sense of astronomical interferometric data and address issues such as the large gaps in data from radio telescopes in different locations.
Bouman also used a machine-learning algorithm to identify visual patterns that tend to recur in 64-pixel patches of real-world images, and she used those features to further refine her algorithm’s image reconstructions.
In separate experiments, according to the MIT note, she extracted patches from astronomical images and from snapshots of terrestrial scenes, but the choice of training data had little effect on the final reconstructions.
Further, Bouman prepared a large database of synthetic astronomical images and the measurements they would yield at different telescopes, given random fluctuations in atmospheric noise, thermal noise from the telescopes themselves, and other types of noise. She made her test data publicly available online for other researchers to use.
Incidentally, the image shows the “extraordinary accuracy of the world’s very first simulation of a black hole 40 years earlier" by Jean-Pierre Luminet, then a young researcher at the CNRS (French National Center for Scientific Research), according to a 10 April press statement.
Published in 1979 in Astronomy & Astrophysics, it caught the attention of the scientific world because it was not an artist’s view, but an image based on the then supposed physical properties of a black hole and its gas disc, such as its rotation rate and temperature, and on Einstein’s general theory of relativity.
Luminet is currently a CNRS Emeritus Senior Researcher at the Laboratoire d’Astrophysique de Marseille.