Chuck Bednar for redOrbit.com – @BednarChuck
Thanks to alterations made to the instrument late last year, the South Pole Telescope (SPT) has joined the Event Horizon Telescope (EHT) project in the search for and study of black holes.
According to Scientific American, the 10-meter diameter SPT, which is located at Antarctica’s Amundsen-Scott South Pole Station, was originally designed to measure faint, diffuse emissions from the cosmic microwave background, the thermal radiation left over from the Big Bang.
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Last December, University of Arizona-Tucson astronomer and EHT collaborator Dan Marrone and his colleagues made the long, arduous trek to the South Pole to make changes to the instrument so that it would be suitable for use in the project’s ongoing search for black holes.
Typically, the SPT’s dish funnels radiation from the CMB into a camera known as a bolometer, Marrone told the website. The bolometer measured the heat from the sky in a specific direction by sensing how much each of its detectors is heated by accumulated light. However, for it to be used in the EHT project, it required an entirely different type of camera.
The Event Horizon Telescope uses a technique known as Very Long Baseline Interferometry (VLBI) that uses a single-pixel imaging instrument to record the waveform of microwaves that hit the telescope, particularly those with a frequency of 230 GHz, Marrone explained.
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With that lone pixel, astronomers can record footage of “the electric field that the radiation from our targets is creating on the surface of the telescope,” he added. Eventually, during a full run of the EHT, telescopes from all over the world will record this type of footage on eight-terabyte hard drives. All of those movies will then be sent to the MIT Haystack Observatory near Boston, where their data will be compiled using a special type of supercomputer called a correlator.
Studying black holes in the South Pole
Marrone’s team had shipped 13 crates worth of equipment to the Amundsen-Scott South Pole Station before they even departed on December 1, but only two had reached their destination arrived by the time the researchers arrived eight days later. As the remaining equipment slowly found its way to the South Pole, the EHT team did what they could when they could.
“For the first month and a half we were there, every day there was someone soldering with an acetylene torch in our ear, filling the air with weird acrid smoke,” he told Scientific American. By the time the last of the cargo arrived, they kicked it into high-gear. “They were very long days. We’d stagger out at 8 or 8:30 am, come back for lunch or dinner and work until midnight. Christmas, New Year’s, it didn’t matter.”
Marrone and his team finished their installations by mid-January and pointed the modified SPT towards the sky, receiving the first light with its VLBI received during the early morning hours on January 16, local time. This allowed them to create images by scanning the single pixel across the sky and producing maps of the pixel value recorded for each position.
The first official light image, the website said, was a map of carbon monoxide near the center of the Milky Way. A second image depicted the moon at 230 GHz, and instead of seeing reflected light, the image shows heat that is escaping from the lunar surface.
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“Notably the crescent is wider at 1mm than in the optical, because the parts of the moon that have just lost the sunlight are still cooling,” Marrone said. “You can also see real signatures of the dark and light patches that you’re used to seeing with your eye.”
While Scientific Amercian pointed out that these are only test images, they demonstrate that the SPT’s equipment will work, allowing it to officially become part of the Event Horizon Telescope. The next step will be to pair it with another, further away telescope, the website added. The ultimate goal is to get the entire EHT array online so that it can be used to take a picture at the black hole located at the center of our Milky Way galaxy.
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