The Event Horizon Telescope (EHT) Collaboration has conducted test observations, using the Atacama Large Millimeter/submillimeter Array (ALMA) and other facilities, that achieved the highest resolution ever obtained from the surface of Earth.
The Event Horizon Telescope (EHT) Collaboration has conducted test observations, using the Atacama Large Millimeter/submillimeter Array (ALMA) and other facilities, that achieved the highest resolution ever obtained from the surface of Earth. They managed this feat by detecting light from distant galaxies at a frequency of around 345 GHz, equivalent to a wavelength of 0.87 mm. The Collaboration estimates that in future they will be able to make black hole images that are 50% more detailed than was possible before, bringing the region immediately outside the boundary of nearby supermassive black holes into sharper focus. They will also be able to image more black holes than they have done so far. The new detections, part of a pilot experiment, were published today in The Astronomical Journal.
The EHT Collaboration released images of M87*, the supermassive black hole at the centre of the M87 galaxy, in 2019, and of Sgr A*, the black hole at the heart of our Milky Way galaxy, in 2022. These images were obtained by linking together multiple radio observatories across the planet, using a technique called very long baseline interferometry (VLBI), to form a single ‘Earth-sized’ virtual telescope.
To get higher-resolution images, astronomers typically rely on bigger telescopes — or a larger separation between observatories working as part of an interferometer. But since the EHT was already the size of Earth, increasing the resolution of their ground-based observations called for a different approach. Another way to increase the resolution of a telescope is to observe light of a shorter wavelength — and that’s what the EHT Collaboration has now done.
Read more at ESO
Image: This artist’s impression shows the locations of multiple radio observatories across the planet, which participated in a pilot experiment conducted by the Event Horizon Telescope (EHT) Collaboration that obtained the highest-resolution observations from the ground. The test observations detected light from distant galaxies at a wavelength of 0.87 mm and were made with some of the observatories (in red) that are part of the EHT, a virtual Earth-sized telescope. One of these distant, point-like galaxies is represented on the top right, sending out radio signals all the way to Earth.
While non-ideal weather conditions hampered the observations at some of the sites, the team was able to observe multiple galaxies using multiple stations. Robust detections were made using different pairs of telescopes, indicated as glowing dots: the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX) in the Atacama Desert in Chile, ALMA and the IRAM 30-meter telescope in Spain, and ALMA and the Submillimeter Array in Hawaiʻi.
The EHT Collaboration is famous for connecting telescopes around the world, using a technique called very long baseline interferometry, to obtain images of supermassive black holes. Previous EHT observations were made at a wavelength of 1.3 mm. By observing a distant active galaxy at a lower wavelength, researchers were able to capture even higher resolution images without forming a bigger virtual telescope. (Credit:ESO/M. Kornmesser)
