The science behind the black hole image can have powerful applications ::

By Tony Rice, collaborator of WRAL

The first image of a black hole in the center of the Messier 87 galaxy published this week is amazing. The technology developed to create it is just as amazing. The Event Horizon Telescope (EHT) project brought together a network of 10 telescopes around the world to see, as the project director, Sheered Doeleman, said "what we thought was incomprehensible."

Einstein first theorized the existence of black holes 100 years ago, while developing his theory of general relativity. Since then, there has been a great deal of evidence that supports the existence of bottom holes, and simulations of how they would look, because it had not been directly observed.

So, what took so long? Why have not we used something like the Hubble Space Telescope (HST) to take this picture?

While the black hole in M87 is as wide as our solar system, it is also 55 million light years away, which makes it very, very small in our sky. Each pixel in the WFC3 camera of HST is approximately 1,250 times wider than the black hole. A telescope as large as Earth was needed, so one was created, virtually.

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Radio telescopes in Hawaii, Arizona, Spain, Mexico, Chile and Antarctica joined in a process called Long-Range Baseline Interferometry to create a single virtual telescope as large as Earth, producing five petabytes of data. That's roughly the size of the Library of Congress's digital collection or the equivalent of 190 continuous years of streaming Netflix in high definition.

This is not only an achievement in astronomy, it is an achievement in data science, in particular the reduction of data and the construction of images from scarce data.

Even with so much data and all that processing, there were still many gaps. This is like putting together a puzzle where 90 percent of the pieces are missing and you do not even know what the final image looks like. So, where does the confidence come from that the image published this week is accurate? The answer lies in data science.

The petabytes were reduced to terra-bytes through the correlation of the observations between the radio telescopes, which take into account aspects such as the rotation of the Earth during the observations and the amount of water vapor in the atmosphere on each telescope. Drought conditions in the Atacama desert, in northern Chile, where one of the telescopes is located, helped make this easier. This step also helps to extract useful data from noise, a common problem in data science.

The EHT was divided into teams that created algorithms independently to further reduce the data in an image, even trying to put together a puzzle with infinite possibilities, with missing pieces and without a box with an image to refer to. Each one constructed algorithms that reduced those infinite possibilities to only those that made physical sense. They returned together last July to share their work and knew they had solved the problem when the teams produced surprisingly similar results.

The resulting image processing techniques and libraries developed by the team could have far-reaching applications in fields that need to build useful images from scarce data, such as medical images and self-driving vehicles.

This black hole also now has a name, Pōwehi, which means "dark fountain embellished with endless creation". The name comes from Kumulipo, the primordial song that describes the creation of the Hawaiian universe, and reflects the role of Mauna Kea's observatories in the creation of the image.

The Hawaiian astronomers on the project consulted with Larry Kimura of the University of Hawaii at the Hawaiian Language College of Hilo. The governor of Hawaii, David Ige, declared April 10 "Powehi's Day".

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You can see Pōwehi, or at least where it is in the southeast sky, after sunset. Look for the question mark to the back that forms the front of the constellation Leo the Lion, then look for the bright star Spica in the constellation Virgo. The galaxy M87 and Pōwehi are approximately 1/3 of the way between the left shoulder of Virgo and the tail of Leo.

Tony Rice is a volunteer in the NASA / JPL Solar System Ambbadador program and software engineer at Cisco Systems. You can follow him on twitter @rtphokie.

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