Evrim Yazgin
Cosmos science journalist
The Event Horizon Telescope (EHT) Collaboration has made the highest resolution observations from the surface of Earth as it gears up to take images of black holes in distant galaxies.
The new results have made crisper images of the supermassive black holes at the centres of the Messier 87 and Milky Way galaxies (the black holes referred to as M87* and Sagittarius A*). The international team’s study is published in the Astronomical Journal.
As a result, M87* and Sagittarius A* images taken in 2019 and 2022 respectively – the first ever images of black holes – have been made 50% clearer. The EHT also produced multi-colour views of the region around the black holes, giving insight into the nature of these mysterious cosmic monsters.
The new images detected light at the higher frequency of 345 GHz, compared to 230 GHz in the old images.
“With the EHT, we saw the first images of black holes by detecting radio waves at 230 GHz, but the bright ring we saw, formed by light bending in the black hole’s gravity still looked blurry,” says co-lead author Alexander Raymond, at NASA’s Jet Propulsion Laboratory (NASA-JPL).
“We were at the absolute limits of how sharp we could make the images.
“At 345 GHz, 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.”
EHT is effectively an Earth-sized telescope, linking multiple radio dishes around the world. Higher resolution images are created by either increasing the distance between dishes or observing at higher frequencies.
Co-lead author Sheperd “Shep” Doeleman – from the Center for Astrophysics | Harvard & Smithsonian (CfA) and Smithsonian Astrophysical Observatory (SAO) – likens the EHT’s “breakthrough” observing at higher frequencies to the transition from black and white to colour photos.
“This new ‘colour vision’ allows us to tease apart the effects of Einstein’s gravity from the hot gas and magnetic fields that feed the black holes and launch powerful jets that stream over galactic distances,” Doeleman says.
Einstein’s general theory of relativity says that gravity bends light of all frequencies in the same way. Therefore, the size of the ring of material around the black hole will be the same size at 230 GHz and 345 GHz, but the details in the image will look different.
It is the first time linked radio telescopes have achieved observations at 345 GHz because this frequency of light is more easily absorbed by our atmosphere.
The next step for the EHT Collaboration is to add new antennas and upgrading existing ones to make the Earth-sized telescope able to work at frequencies between 100 GHz and 345 GHz at the same time.
