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Massive telescope array aims for black hole, gets gusher of data

Lucas Mearian | Aug. 19, 2015
Astronomers have turned to helium-filled hard drives to capture the petabytes of data coming from the Event Horizon Telescope

Antennas of the Atacama Large Millimeter/submillimeter Array
Antennas of the Atacama Large Millimeter/submillimeter Array (ALMA), on the Chajnantor Plateau in the Chilean Andes. The Large and Small Magellanic Clouds, two companion galaxies to our own Milky Way galaxy, can be seen as bright smudges in the night sky, in the centre of the photograph. The ALMA Array is also a part of the Event Horizon Telescope project. Credit: ESO/C. Malin

Astronomers developing the Event Horizon Telescope (EHT), a synchronized network of radio antennas with a viewing field as large as the Earth, hope to soon take the first ever photo of Sagittarius A*, a massive black hole at the center of the Milky Way.

The amount of data being collected by 10 radio antennas around the globe, often located atop mountains, has forced the astronomers to turn to helium-filled hard drives for their data storage.

For example, one of the radio telescopes that make up the EHT array is located 15,000 feet above sea level at the top of the Sierra Negra, an extinct volcano in Mexico. When researchers attempted to collect data using 32 conventional hard drives, 28 of them failed.

apex antenna
The Apex antenna, which is part of the Event Horizon Telescope, is located 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert in Chile.  Credit: Lars Lindberg Christensen

"We couldn't use them because the air pressure was so low that the drive heads kept crashing on the hard drive platters," said Shep Doeleman, who directs the EHT project.

Doeleman, a professor at the Harvard-Smithsonian Center for Astrophysics/Massachusetts Institute of Technology, said helium-filled hard drives, which are hermetically sealed from outside air, not only solved the low-pressure problem, but also offered far greater storage capacity. Each of the helium-filled drives from Western Digital's HGST division stores 8TB of data, compared to the 4TB drives the researchers had been using.

Hard drive capacity is crucial in that the EHT array collects data at 64Gbps. Over a typical five-day data collection campaign, each radio telescope collects 900TB of data. That data is then stored on from 1,000 to 2,000 hard drives, which amounts to about 7 petabytes (PB) of data total over five days, Doeleman said.

Data collected from the EHT array is correlated, and the signal that results is the equivalent to a single focused spot in the black hole.

Each year since its first data capture in 2006, the EHT array has moved to add new sites around the world. This year, the project hopes to add telescopes in France, Greenland, the U.S. and the South Pole.


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