These new observations, combined with previous images of supermassive black holes at the lower frequency of 230 GHz, will enhance the clarity of black hole photographs by 50%. They will also enable multi-color views of the regions just outside the event horizons of these enigmatic objects.

Led by scientists from the Center for Astrophysics | Harvard and Smithsonian (CfA), including the Smithsonian Astrophysical Observatory (SAO), the findings were published in 'The Astronomical Journal'.

"With the EHT, we saw the first images of black holes by detecting radio waves at 230 GHz, but the bright ring we saw, formed by light bending in the black hole's gravity, still looked blurry because we were at the absolute limits of how sharp we could make the images," explained paper co-lead Alexander Raymond, formerly a postdoctoral scholar at the CfA and now at NASA's Jet Propulsion Laboratory (NASA-JPL). "At 345 GHz, our images will be sharper and more detailed, which in turn will likely reveal new properties, both those that were previously predicted and maybe some that weren't."

The EHT operates by linking multiple radio dishes worldwide, creating a virtual Earth-sized telescope using a technique known as very-long-baseline interferometry (VLBI). To achieve higher-resolution images, astronomers either need to increase the distance between the radio dishes or observe at a higher frequency. With the EHT already spanning the globe, enhancing resolution necessitated expanding the frequency range, a goal the EHT Collaboration has now realized.

"To understand why this is a breakthrough, consider the burst of extra detail you get when going from black and white photos to color," noted paper co-lead Sheperd "Shep" Doeleman, an astrophysicist at the CfA and SAO, and Founding Director of the EHT. "This new 'color vision' allows us to tease apart the effects of Einstein's gravity from the hot gas and magnetic fields that feed the black holes and launch powerful jets that stream over galactic distances."

This achievement marks the first successful use of the VLBI technique at a frequency of 345 GHz. While single telescopes have observed the sky at this frequency before, applying the VLBI method at 345 GHz posed significant challenges that took time and technological advances to overcome. Atmospheric water vapor absorbs waves at this frequency much more than at 230 GHz, weakening signals from black holes. Researchers enhanced the EHT's sensitivity by increasing the bandwidth of the instruments and waiting for optimal weather conditions at all sites.

The new experiment utilized two small subarrays of the EHT, consisting of the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX) in Chile, the IRAM 30-meter telescope in Spain, the NOrthern Extended Millimeter Array (NOEMA) in France, the Submillimeter Array (SMA) on Maunakea in Hawai'i, and the Greenland Telescope. These instruments together achieved resolutions as fine as 19 microarcseconds.

"The most powerful observing locations on Earth exist at high altitudes, where atmospheric transparency and stability is optimal but weather can be more dramatic," said Nimesh Patel, an astrophysicist at the CfA and SAO, and a project engineer at SMA. He added that the new observations required braving icy roads at Maunakea to open the array in stable weather just minutes after a snowstorm. "Now, with high-bandwidth systems that process and capture wider swaths of the radio spectrum, we are starting to overcome basic problems in sensitivity, like weather. The time is right, as the new detections prove, to advance to 345 GHz."

This progress also represents a critical step toward creating high-fidelity movies of the event horizon environments surrounding black holes. Future upgrades, such as the next-generation EHT (ngEHT) project, will add new antennas in strategically located sites and enhance existing stations to operate at multiple frequencies between 100 GHz and 345 GHz simultaneously. These upgrades are expected to increase the clarity and quantity of data by a factor of 10, enabling scientists to produce even more detailed and dynamic images and movies of these cosmic phenomena.

"The EHT's successful observation at 345 GHz is a major scientific milestone," said Lisa Kewley, Director of CfA and SAO. "By pushing the limits of resolution, we're achieving the unprecedented clarity in the imaging of black holes we promised early on and setting new and higher standards for the capability of ground-based astrophysical research."

Research Report:First Very Long Baseline Interferometry Detections at 870 um

Related Links
Event Horizon Telescope (EHT)
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