2024-09-04 08:15:16
The Event Horizon Telescope (EHT) has made the highest resolution test observations yet from the Earth’s surface. This feat was achieved by detecting light from distant galaxies at a frequency of around 345 GHz, equivalent to a wavelength of 0.87 mm. This improvement will increase the sharpness of images of supermassive black holes and allow the astronomical community to image more black holes than ever before.
Beginning in 2019, the EHT Collaboration (the team of scientists running the EHT) published images of the supermassive black hole at the center of the galaxy M87 and, in 2022, images of Sgr A*, the black hole at the heart of our galaxy. , Milky Way. These images were obtained by linking together several radio observatories scattered around the planet, using a technique called very long baseline interferometry (VLBI), to create one virtual radio telescope the size of Earth.
To obtain high-resolution images, the astronomical community often turns to larger telescopes (or greater separation between observatories acting as part of an interferometer). However, since the EHT was already the size of Earth, a different approach was needed to increase the resolution of its observations of Earth. Another way to increase the resolution of a telescope is to look at shorter wavelength light, which is what the EHT Collaboration has now done.
To demonstrate that they could make a detection at 0.87 mm, the EHT Collaboration made test observations of distant bright galaxies at this wavelength. Instead of using the full set of the EHT, they used two smaller subsets. Both included the ALMA (Atacama Large Millimeter/submillimeter Array) and the APEX (Atacama Pathfinder Experiment) in the Atacama Desert in Chile. Other facilities used included the 30-meter IRAM radio telescope in Spain and the NOEMA (Northern Extended Millimeter Array) in France, as well as the Greenland Radio Telescope and the Submillimeter Array in Hawaii.
In this pilot experiment, the EHT Collaboration achieved observations with details of up to 19 microseconds, the highest resolution ever achieved from the Earth’s surface. Although there are records of high-resolution observations, these signals from instruments located on Earth combine with others located in space. However, they were unable to obtain images: although strong light detections were found from several distant galaxies, these test observations did not use enough antennas to accurately reconstruct an image of them.
This diagram shows the location of several radio observatories around the planet, which participated in the experiment carried out by the EHT (Event Horizon Telescope) Collaboration. The experiment obtained the highest observations of its kind from Earth. The test observations of light from distant galaxies at a wavelength of 0.87 mm were detected by several of the observatories (in red) that are part of the EHT, a virtual Earth-sized radio telescope. One of these distant galaxies is in the shape of a dot at the top right, sending radio signals to Earth. Although weather prevented observations at some of the sites, the team was able to see multiple galaxies using multiple stations. Strong detections were made using different pairs of telescopes: the ALMA (Atacama Large Millimeter/submillimeter Array) and the APEX (Atacama Pathfinder Experiment) in the Atacama Desert in Chile; the ALMA and the IRAM 30-meter radio telescope in Spain, and the ALMA and the Submillimeter Array in Hawaii. (Image: ESO / M. Kornmesser. CC LE 4.0)
This is the first time the VLBI technique has been used successfully at the 0.87 mm wavelength. Although the ability to observe the night sky at 0.87 mm preceded the new detectors, the use of the VLBI technique at this wavelength has always presented challenges that have taken time and technological progress. For example, water vapor in the atmosphere absorbs waves at 0.87 mm much more than at 1.3 mm, making it harder for radio telescopes to pick up signals from black holes at shorter wavelengths. Coupled with increasingly significant atmospheric turbulence, noise accumulation at shorter wavelengths, and the inability to monitor global weather conditions during atmospherically sensitive observations, progress towards shorter wavelengths has been slow for VLBI, especially those that cross the barrier towards the sub-millimeter. But with these new sensors, everything has changed.
This technical test opened a new window into the study of black holes. With the full array, the EHT could see data in as little as 14 microarcseconds, equivalent to seeing a grape on the Moon from Earth. There is also the potential to see smaller and more distant black holes than those imaged so far by the EHT Collaboration.
The EHT Collaboration involves more than 400 researchers from Africa, Asia, Europe and North and South America, and there are approximately 270 participants in this large-scale experiment. The authors have detailed the experiment in the academic journal The Astronomical Journal.
The ALMA observatory is the result of a partnership between the European Southern Observatory (ESO), the National Science Foundation (NSF) of the United States and the National Institutes of Natural Sciences (NINS) of Japan, together with NRC (Canada), NSTC and ASIAA (Taiwan ), and KASI (Republic of South Korea), in cooperation with the Republic of Chile. (Source: ALMA Observatory)
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