Astrophysicists from the Event Horizon Telescope (EHT) Collaboration have conducted test observations that achieve the highest resolution ever obtained from Earth’s surface by detecting light emanating from the center of a distant galaxy at a frequency of about 345 GHz. When combined with existing images of the supermassive black hole at the center of Messier 87 and the Milky Way galaxy at a lower frequency of 230 GHz, these new results not only produce a 50% sharper picture of the black hole, but also a multi-color image of the region just outside the boundaries of these cosmic monsters.
This artist’s impression shows the locations of radio observatories on Earth that took part in the EHT Collaboration’s pilot experiment to produce the highest-resolution observations from the ground. Image courtesy of ESO/M. Kornmesser.
In 2019, the EHT Collaboration released images of M87*, the supermassive black hole at the center of Messier 87, and in 2022, they released images of Sagittarius A*, the supermassive black hole at the center of the Milky Way galaxy.
These images were obtained by linking multiple radio observatories around Earth, using a technique called Very Long Baseline Interferometry (VLBI), to form a single “Earth-sized” virtual telescope.
To get higher resolution images, astronomers typically resort to larger telescopes, or greater distances between observatories acting as part of an interferometer.
But because the EHT was already the same size as Earth, a different approach was needed to increase the resolution of ground-based observations.
Another way to increase a telescope’s resolution is to observe shorter wavelengths of light, and that’s exactly what the EHT Collaboration is currently doing.
“The EHT has seen the first image of a black hole at 1.3 millimeter wavelengths, but the bright ring created by the black hole’s gravity bending light still appears blurry because we’ve reached the absolute limit of how sharp an image we can make,” said Dr Alexander Raymond, an astronomer at NASA’s Jet Propulsion Laboratory.
“At 0.87mm, the images will be clearer and more detailed, which may reveal new properties, some previously predicted, but also some perhaps not.”
To demonstrate detection at 0.87 mm, EHT researchers carried out test observations of distant, bright galaxies at this wavelength.
Rather than using the entire EHT array, they used two smaller subarrays, including ALMA and the Atacama Pathfinder EXperiment (APEX).
Other facilities that will be used include the IRAM Thirty Meter Telescope in Spain, the Northern Extended Millimeter Array (NOEMA) in France, and the Greenland Telescope and Submillimeter Array in Hawaii.
In this pilot experiment, scientists achieved measurements down to 19 microarcseconds, the highest resolution ever achieved from the Earth’s surface.
But it hasn’t yet been able to capture an image: Though it has robustly detected light from some distant galaxies, it hasn’t used enough antennas to be able to accurately reconstruct an image from the data.
This technical test opens up new avenues for studying black holes.
With the full array, the EHT can see details as small as 13 microarcseconds, the equivalent of seeing a bottle cap on the Moon from Earth.
This means that at 0.87mm we can obtain images with approximately 50% higher resolution than the previously published M87* and Sagittarius A* 1.3mm images.
What’s more, it may be possible to observe a black hole that is more distant, smaller and fainter than the two black holes imaged so far.
“Observing changes in the surrounding gas at different wavelengths will help us solve the mysteries of how black holes attract and accrete matter, and how they can launch powerful jets that travel across the Milky Way galaxy,” said Dr Shepard Doleman, EHT founding director and astrophysicist at the Harvard-Smithsonian Center for Astrophysics.
This is the first time that VLBI technology has been used successfully at a wavelength of 0.87 mm.
“The detection of a VLBI signal at 0.87 mm is groundbreaking as it opens a new observational window into the study of supermassive black holes,” said Dr Thomas Krichbaum, astrophysicist at the Max Planck Institute for Radio Astronomy.
“In the future, the Spanish and French IRAM telescopes in combination with ALMA and APEX will allow us to image smaller and fainter radiation simultaneously at two wavelengths, 1.3 mm and 0.87 mm, which was previously possible.”
Team paper Published in Astronomical Journal.
_____
Alexander W. Raymond others2024. First Very Long Baseline Interferometry Detection 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: www.sci.news
