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Groton Scientists Help Bring Image of Black Hole To Earth

Aerial view of MIT Haystack Observatory, a discreet and shy presence in the area, has burst into internationl public recognition with the first image of a black hole.

Graphic showing Groton/Westford townline and MIT Linclon Labs land in Groton with relative position of Transfer Station in relation to Haystack Observatory.

by Russell Harris

   MIT Lincoln Labs and Haystack Observatory - just across the far eastern border of the town in Westford - has been a discreet, shy and private presence in Groton since its founding in the 1950s.With almost 130 forested acres in Groton buffering Haystack Observatory from public view just across the town line in Westford [see map page 3], and MIT’s very low-profile here, it would be hard to know the Observatory existed but for the ghostly domes of radio telescopes peeking above the horizon when looking east from Groton’s Transfer Station or the soccer fields at Cow Pond Brook.

   MIT Lincoln Labs has been working in Groton/Westford for 60 plus years  when MIT conducted military radar research for detecting intercontinental ballistic missiles and other associated work. Since then, Haystack has focused on basic astrophysical research while keeping a very low public profile. 

   But now, with an image of a black hole released to the world, the public’s awareness of Haystack Observatory as a leader in advancing scientific knowledge has taken off like a rocket. 

   Along with the Haystack’s raised profile, is local awareness that five Groton scientists and technologists were contributors to the 200-member team that made the dream of imaging a black hole reality. Among the Groton residents are John Barrett, Roger Cappallo, Joseph Crowley, Kevin Dudevoir, Michael Titus and Senior Scientist, Alan Rogers, of Ayer.

   Taking a picture of a black hole was a scientific ‘impossible dream’ for decades. But, as more telescopes were built on mountaintops around the world, the dream gradually gave way to a vague awareness that capturing an image of a black hole might be possible.

   MIT Professor Sheperd Doeleman suggested how such an image could be made while working at Haystack Observatory in the early 2000s. He proposed a planet-scale array of radio telescopes across the globe - all working together -  in effect turning the whole earth into a giant telescope.

   He named this networked telescope concept the Event Horizon Telescope [EHT] when leading this pioneering work at Haystack.

   Around this time, Haystack engineers started developing the digital tools that would be needed to make an EHT reality - skills at which Haystack engineers have long excelled - including very high speed digital recorders, and a correlator that could process the enormous datastreams that an array of disparate telescopes would give off.

     In 2007, Haystack put the EHT idea to the test, installing Haystack’s custom-designed digital recorders on three radio telescopes scattered around the world and aiming them together at the black hole at the center of our own galaxy.

   “We didn’t have enough dishes to make an image,” recalled a leader of the EHT science operations working group. But the proof of concept worked because they could image an object that was about the right size. 

   On any given day, telescopes  worldwide operate independently, focused on various astrophysical objects.  But, when multiple radio telescopes, separated by very large distances, are synchronized and focused on an object in the sky, they can operate as a single large radio dish through a technique known as very long baseline interferometry, or VLBI. 

  Thus, an array of participating EHT telescopes could become a virtual radio dish as big as the Earth, with the ability to ‘see’ an object about 3 million times sharper than 20/20 vision.

  On April 5, 2017, the EHT with eight participating telescopes, began observing their target galaxy, 50 million light years away. 

      The data collection began after consulting numerous weather forecasts, astronomers identified four nights that would produce clear conditions for the eight participating observatories — a rare opportunity, during which they could work as one collective dish to observe the target black hole at M87.      The Haystack-designed digital recorders began recording huge amounts of data at each site. In total, each telescope took in about one petabyte of data, equal to 1 million gigabytes. Each station recorded this enormous stream of data onto ultrafast data recorders developed at Haystack.

After the run ended, researchers packed up the stacks of hard drives at each station and flew them via FedEx to Haystack Observatory, in Westford and Max Planck Institute for Radio Astronomy, in Germany. 

  The data volumes were so massive, that air transport was much faster than transmitting the data electronically. At both Haystack and the Max Planck Institute, , the data were played back into a highly specialized supercomputer called a correlator, which processed the data two streams at a time.

   Teams at both Haystack and Max Planck then began the painstaking process of “correlating” the data, identifying a range of problems at the different telescopes, fixing them, and rerunning the correlation, until the data could be rigorously verified. Only then were the data released to four separate teams around the world, each tasked with generating an image from the data using independent techniques.

   “It was the second week of June, and I remember I didn’t sleep the night before the data was released, to be sure I was prepared,” says Kazunori Akiyama, co-leader of the EHT imaging group and a postdoc working at Haystack.

   All four imaging teams previously tested their algorithms on other astrophysical objects, making sure that their techniques would produce an accurate visual representation of the radio data. When the files were released, Akiyama and his colleagues immediately ran the data through their respective algorithms. Importantly, each team did so independently of the others, to avoid any group bias in the results.

   “The first image our group produced was slightly messy, but we saw this ring-like emission, and I was so excited at that moment,” Akiyama remembers. “But simultaneously I was worried that maybe I was the only person getting that black hole image.”

   His concern was short-lived. Soon afterward all four teams met at the Black Hole Initiative at Harvard University to compare images, and found, with some relief, and much cheering and applause, that they all produced the same, lopsided, ring-like structure — the first direct images of a black hole.

 

Ed Note: Large portions of this story, especially the later half, were taken from and rewritten from an MIT News Release written by Jennifer Chu. 

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