Astrophysicists with the Event Horizon Telescope (EHT) Collaboration have conducted test observations achieving the highest resolution ever obtained from the surface of the Earth, by detecting light from the centers of distant galaxies at a frequency of around 345 GHz. When combined with existing images of supermassive black holes at the hearts of Messier 87 and our Milky Way Galaxy at the lower frequency of 230 GHz, these new results will not only make black hole photographs 50% crisper but also produce multi-color views of the region immediately outside the boundary of these cosmic beasts.
This artist’s impression shows the locations of multiple radio observatories across the planet, which participated in a pilot experiment conducted by the EHT Collaboration that obtained the highest-resolution observations from the ground. Image credit: ESO / M. Kornmesser.
The EHT Collaboration released images of M87*, the supermassive black hole at the center of Messier 87, in 2019, and of Sagittarius A*, the supermassive 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.
“With the EHT, we saw the first images of black holes using the 1.3-mm wavelength observations, 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,” said Dr. Alexander Raymond, an astronomer at NASA’s Jet Propulsion Laboratory.
“At 0.87 mm, 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.”
To show that they could make detections at 0.87 mm, the EHT researchers conducted test observations of distant, bright galaxies at this wavelength.
Rather than using the full EHT array, they employed two smaller subarrays, both of which included ALMA and the Atacama Pathfinder EXperiment (APEX).
Other facilities used include the IRAM 30-m telescope in Spain and the NOrthern Extended Millimeter Array (NOEMA) in France, as well as the Greenland Telescope and the Submillimeter Array in Hawai’i.
In this pilot experiment, the scientists achieved observations with detail as fine as 19 microarcseconds, meaning they observed at the highest-ever resolution from the surface of Earth.
They have not been able to obtain images yet, though: while they made robust detections of light from several distant galaxies, not enough antennas were used to be able to accurately reconstruct an image from the data.
This technical test has opened up a new window to study black holes.
With the full array, the EHT could see details as small as 13 microarcseconds, equivalent to seeing a bottle cap on the Moon from Earth.
This means that, at 0.87 mm, they will be able to get images with a resolution about 50% higher than that of previously released M87* and Sagittarius A* 1.3-mm images.
In addition, there’s potential to observe more distant, smaller and fainter black holes than the two they have imaged thus far.
“Looking at changes in the surrounding gas at different wavelengths will help us solve the mystery of how black holes attract and accrete matter, and how they can launch powerful jets that stream over galactic distances,” said EHT founding director Dr. Sheperd Doeleman, an astrophysicist at the Harvard & Smithsonian’s Center for Astrophysics.
This is the first time that the VLBI technique has been successfully used at the 0.87 mm wavelength.
“These VLBI signal detections at 0.87 mm are groundbreaking since they open a new observing window for the study of supermassive black holes,” said Dr. Thomas Krichbaum, an astrophysicist at the Max Planck Institute for Radio Astronomy.
“In the future, the combination of the IRAM telescopes in Spain and France with ALMA and APEX will enable imaging of even smaller and fainter emission than has been possible thus far at two wavelengths, 1.3 mm and 0.87 mm, simultaneously.”
The team’s paper was published in the Astronomical Journal.
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Alexander W. Raymond et al. 2024. First Very Long Baseline Interferometry Detections at 870 μm. AJ 168, 130; doi: 10.3847/1538-3881/ad5bdb
This article is a version of a press-release provided by ESO.
Source : Breaking Science News