It Took Half a Ton of Hard Drives to Store the Black Hole Image Data

The newly released image of a black hole (below) is a watershed moment for physics. Finally, we can put some of Einstein’s most famous predictions from a century ago to the test, but it was not as easy as pointing a big lens at the M87 galaxy and pressing a button. It took years of work and the collaboration of more than 200 scientists to make it happen. It also required about half a ton of hard drives.

Data collection for the historic black hole image began in 2017 with a coordinated effort called the Event Horizon Telescope (EHT). That isn’t a single instrument but rather a collection of seven radio telescopes from around the world. The EHT used a principle called interferometry to combine the capacity of all those telescopes, creating a “virtual” telescope the size of the Earth.

The EHT had to collect a huge volume of data to deliver us this one image. Dan Marrone, Associate Professor of Astronomy at the University of Arizona says the EHT team had to install specialized super-fast data recorders on the various radio telescopes to handle the influx of measurements.

The now-famous image of a black hole comes from data collected over a period of seven days. At the end of that observation, the EHT didn’t have an image — it had a mountain of data. Scientists like MIT’s Katie Bouman (above) had to develop algorithms to take 5 petabytes of data and make sense of it. But how do you get all that data to the correlation teams in the US and Germany? You use an airplane.

According to Marrone, 5 petabytes is equal to 5,000 years of MP3 audio. There’s simply no way to send that much data efficiently over the internet. It’s faster to actually ship the hard drives to collaborators around the world. That’s why MIT has 1,000 pounds of hard drives sitting in its Haystack Observatory labs.

Jason Snell at Six Colors has helpfully worked out the effective data rate of shipping these hard drives. The Mauna Kea Observatory in Hawaii might have generated about 700TB of data (one-seventh of the total), and it’s 5,000 miles from MIT in Boston. Figuring in trips to and from the airport and the flight itself, it took around 50,400 seconds to move the data. While the best internet connections are currently measured in a few gigabits per second, shipping those drives from Hawaii to MIT works out to 14 gigabytes per second (112 gigabits per second).

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