The Event Horizon Telescope has achieved unprecedented high-resolution views from Earth using the 345 GHz frequency, providing more detailed and colorful images of black holes.
This advance in astrophysics exploits very long baseline interference to link multiple radio dishes globally, enhancing our understanding of the phenomena surrounding black holes and paving the way for future high-resolution visualizations and potential real-time imaging of these cosmic entities.
Breakthrough in black hole imaging
The Event Horizon Telescope (EHT) project has successfully conducted test observations that achieved the highest resolution ever obtained from the Earth’s surface, by detecting light coming from the centers of distant galaxies at a frequency of about 345 gigahertz.
Combined with existing images of the supermassive black holes at the heart of M87 and Sgr A at the low frequency of 230 GHz, these new results will not only make us study this phenomenon more difficult. Black hole The images are 50% sharper but also produce multi-colored views of the area just beyond the boundaries of these cosmic monsters.
Improvements in radio astronomy
New discoveries led by scientists from the Center for Astrophysics | Harvard and Smithsonian (CFA) which includes the Smithsonian Astrophysical Observatory (SAO), was published today in Astronomical Journal.
“With the Event Horizon Telescope, we saw the first images of black holes by detecting radio waves at 230 GHz, but the bright ring we saw, formed by the bending of light in the black hole’s gravity, still looked blurry because we were at the absolute limit of how sharp we could get images,” said Alexander Raymond, a co-author of the paper, who was a postdoctoral researcher at the Harvard Center for the Fine Arts and is now at the Harvard Center for the Fine Arts. NASANASA’s Jet Propulsion LaboratoryJet Propulsion Laboratory“At 345 GHz, our images will be much sharper and more detailed, which should reveal new properties, both those previously predicted and perhaps some that were not predicted.”
Earth-Sized Virtual Telescope: Unleashing the Power of the EHT
The EHT creates a virtual Earth-sized telescope by linking multiple radio dishes across the globe, using a technique called very long baseline interferometry (VLBI). To get higher-resolution images, astronomers have two options: increase the distance between the radio dishes or observe at a higher frequency. Since the EHT was already the size of our planet, increasing the resolution of ground-based observations required extending its frequency range, which is what the EHT collaboration has now done.
“To understand why this is such a breakthrough, think about the explosion of extra detail you get when you go from black-and-white to color,” said Shepard “Chip” Doeleman, a co-author of the paper, an astrophysicist at the Cambridge Fine Arts Centre and Sotheby’s Observatory, and founding director of the Event Horizon Telescope. “This new ‘color vision’ allows us to separate the effects of Einstein’s gravity from the hot gas and magnetic fields that fuel black holes and launch powerful jets that stream across galactic distances.”
The prism splits white light into a rainbow of colors because different wavelengths of light travel at different speeds through the glass. But gravity bends all light in a similar way, so Einstein expected the rings seen by the EHT to look the same at both 230 GHz and 345 GHz, while the hot gas swirling around black holes would look different at those two frequencies.
Overcoming Technological Challenges in High-Frequency VLBI
This is the first time VLBI has been successfully used at 345 GHz. While the ability to observe the night sky with individual telescopes at 345 GHz has existed before, using VLBI at this frequency has long presented challenges that took time and technological advances to overcome. Water vapor in the atmosphere absorbs waves at 345 GHz much more than at 230 GHz, weakening signals from black holes at the higher frequency. The key was to improve the sensitivity of the EHT, which the researchers did by increasing the bandwidth of the instruments and waiting for good weather at all locations.
Global cooperation and advanced technology
The new experiment used two small subsets of the EHT – consisting of the Atacama Large Millimeter/submillimeter Array (pain) 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 Mauna Kea in Hawaii, and the Greenland Telescope—to make measurements with resolutions down to 19 microarcseconds.
“The most powerful observing sites on Earth are at high altitudes, where atmospheric transparency and stability are ideal but weather can be more dramatic,” said Nimesh Patel, an astrophysicist at CfA and SAO, and a project engineer for SMA, adding that at SMA, the new observations required braving the icy roads of Mauna Kea to open the array in stable weather after a snowstorm with extra minutes. “Now, with high-bandwidth systems that process and capture wider swaths of the radio spectrum, we are beginning to overcome fundamental sensitivity issues, such as weather. The time is right, as the new findings demonstrate, to advance to 345 GHz.”
The Future of Black Hole Imaging: The ngEHT Project
This achievement also provides another milestone on the path to creating high-resolution movies of the event horizon environment surrounding black holes, which will rely on upgrades to the current Global Array. The planned Next Generation EHT (ngEHT) project will add new antennas to the EHT at improved geographic locations and enhance the existing stations by upgrading them all to operate on multiple frequencies between 100 GHz and 345 GHz simultaneously. As a result of these and other upgrades, the Global Array is expected to increase the amount of sharp, clear data the EHT has to image by a factor of 10, allowing scientists to produce not only more detailed and sensitive images but also movies starring these violent cosmic beasts.
A major achievement in the field of astrophysics research
“The successful EHT observation at 345 GHz represents a major scientific achievement,” said Lisa Kewley, director of the CfA Centre and SAO. “By pushing the limits of resolution to the limit, we are achieving the unprecedented clarity in black hole imaging that was promised early on, and setting new and higher standards for ground-based astrophysical research capability.”
To learn more about this discovery, see Black Holes Observed at Never Before High Frequencies.
Reference: “First detections of very long baseline interference at 870 μm” by A. W. Raymond and S. Doeleman et al., 27 August 2024, Astronomical Journal.
DOI: 10.3847/1538-3881/ad5bdb