The Event Horizon Telescope (EHT) Collaboration has achieved the highest resolution ever obtained from Earth’s surface. In recent tests, they detected light from the centers of distant galaxies at a frequency of around 345 GHz. These new results promise to make black hole photographs 50% sharper. When combined with existing images at 230 GHz, they will also provide multi-color views of the regions surrounding these cosmic giants.
The Center for Astrophysics | Harvard & Smithsonian (CfA), including the Smithsonian Astrophysical Observatory (SAO), led these groundbreaking detections. The results were published today in The Astronomical Journal.
“With the EHT, we captured the first images of black holes using radio waves at 230 GHz,” explained Alexander Raymond, co-lead of the study. “However, the bright ring we observed, formed by light bending due to the black hole’s gravity, still appeared blurry. At 345 GHz, our images will be sharper and more detailed, likely revealing new properties—some predicted, others unexpected.”
The EHT creates a virtual Earth-sized telescope by linking multiple radio dishes worldwide using very-long-baseline interferometry (VLBI). To enhance image resolution, astronomers can either increase the distance between the radio dishes or observe at a higher frequency. Since the EHT already spans the planet, the team focused on expanding its frequency range.
A New Era of Black Hole Imaging
“To grasp the significance of this breakthrough, think about the extra detail you see when switching from black-and-white photos to color,” said Sheperd “Shep” Doeleman, co-lead of the study and Founding Director of the EHT. This “color vision” will help scientists distinguish the effects of Einstein’s gravity from the hot gas and magnetic fields that surround black holes and fuel their powerful jets.
Gravity bends all light similarly, meaning Einstein’s theory predicts that the size of the rings seen by the EHT should be nearly the same at 230 GHz and 345 GHz. However, the hot gas swirling around the black holes will appear differently at these frequencies.
This marks the first successful use of the VLBI technique at 345 GHz. Although individual telescopes could observe the night sky at this frequency before, applying VLBI at 345 GHz has long been a challenge. Water vapor in the atmosphere absorbs waves at this frequency more than at 230 GHz, weakening the signals from black holes. To overcome this, researchers improved the sensitivity of the EHT by increasing the bandwidth of the instruments and waiting for optimal weather conditions at all sites.
The 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) in Hawai’i, and the Greenland Telescope. This setup allowed for measurements with a resolution as fine as 19 microarcseconds.
“The most powerful observing locations on Earth are at high altitudes, where atmospheric transparency and stability are optimal,” said Nimesh Patel, an astrophysicist at the CfA and SAO. He added that the SMA team had to brave icy roads to open the array just after a snowstorm. “With high-bandwidth systems processing wider swaths of the radio spectrum, we are overcoming basic sensitivity problems, like weather. The time is right, as the new detections prove, to advance to 345 GHz.”
Paving the Way for High-Fidelity Black Hole Movies
This achievement is a significant step towards creating high-fidelity movies of the environments around black holes. The planned next-generation EHT (ngEHT) project aims to add new antennas in optimized locations and upgrade existing stations to operate at multiple frequencies between 100 GHz and 345 GHz. These upgrades are expected to increase the clarity of EHT’s data by a factor of 10, enabling scientists to produce not only more detailed images but also movies of these violent cosmic phenomena.
“The EHT’s success at 345 GHz is a major scientific milestone,” said Lisa Kewley, Director of CfA and SAO. “By pushing the limits of resolution, we are achieving unprecedented clarity in black hole imaging and setting new standards for ground-based astrophysical research.”
This breakthrough marks a new era in the study of black holes, promising sharper images and a deeper understanding of these enigmatic cosmic entities.
The Event Horizon Telescope (EHT) Collaboration has achieved the highest resolution ever obtained from Earth’s surface. In recent tests, they detected light from the centers of distant galaxies at a frequency of around 345 GHz. These new results promise to make black hole photographs 50% sharper. When combined with existing images at 230 GHz, they will also provide multi-color views of the regions surrounding these cosmic giants.
The Center for Astrophysics | Harvard & Smithsonian (CfA), including the Smithsonian Astrophysical Observatory (SAO), led these groundbreaking detections. The results were published today in The Astronomical Journal.
“With the EHT, we captured the first images of black holes using radio waves at 230 GHz,” explained Alexander Raymond, co-lead of the study. “However, the bright ring we observed, formed by light bending due to the black hole’s gravity, still appeared blurry. At 345 GHz, our images will be sharper and more detailed, likely revealing new properties—some predicted, others unexpected.”
