Event Horizon Telescope captures highest-resolution images ever taken from the ground

A recent pilot experiment demonstrated new capabilities that can take even sharper images of black holes.

A recent experiment conducted by radio telescopes affiliated with the Event Horizon Telescope obtained the sharpest astronomical images ever taken from the ground. Credit: ESO/M. Kornmesser

The Event Horizon Telescope (EHT) was designed to capture images of some of the most gargantuan structures in the universe — and a new observation just pushed it to its limits.

In a study published in The Astrophysical Journal, scientists working on the EHT — a consortium of 11 radio telescopes spread out across nine locations around the globe that act like one giant telescope — used all of its might to detect light from four galaxies several billion light-years away. The result is the highest resolution telescope image ever taken from the surface of Earth. (There are a few higher resolution images that paired ground-based and space-based observatories.)

The EHT was built to observe the event horizons of black holes with extreme resolution: By linking telescopes around the globe, the network can observe with the resolution of a planet-sized telescope. But this experiment used another strategy to sharpen its vision even further — looking at shorter wavelengths of light. The observations pushed down to wavelengths of 0.87 millimeters, shorter than the 1.3 mm used to observe the supermassive black hole at the center of our galaxy (called Sgr A*) as well as the one at the center of the galaxy Messier 87 (M87*). And the shorter the wavelength, the better the potential resolution.

“It’s kind of like the EHT is getting glasses,” says Sheperd Doeleman, an astrophysicst at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, and the second of hundreds of authors on the paper who are all part of the enormous EHT collaboration.

The new study didn’t rely on all 11 telescopes. Instead, it primarily used the Atacama Large Millimeter-submillimeter Array and the Atacama Pathfinder EXperiment, with additional observations from the IRAM 30-meter telescope in Spain, the NOrthern Extended Millimeter Array in France, the Greenland Telescope, and the Submillimeter Array in Hawaiʻi.

The four galaxies they targeted — J0423−0120, J0510+1800, J0521+1638,411, and J0522−3627 — are frequently used to calibrate telescopes before observing runs. They are also visible to all the telescopes used and are very bright, making them good targets for a test run.

Seeing black holes in a new light

Doeleman says there are a few other important aspects to EHT’s new capabilities — including the ability to image in color. “They’ll be false color images, but you’ll be able to see how Sgr A* or M87 look at different frequencies,” he says. (Most telescope images are in false color to draw out more details.) “Imagine going from black and white to color. You wind up seeing textures, you wind up seeing different reflections at different colors from the environment that’s surrounding you. You see things you didn’t even think to look for because you have this new dimension of color.”

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That will allow the light going into a black hole to be studied in more detail, providing information about how plasma bubbles are generated by black holes.

The members of the EHT consortium plan to target supermassive black holes at the centers of nearby galaxies, enabling a better understanding of these cosmic behemoths. According to a press release from the European Southern Observatory, the level of detail will be “equivalent to seeing a bottle cap on the Moon from Earth.”

The telescopes will also be able to make “movies” from the observations at the new resolution. Sgr A*, because it’s so near to us, will be able to be observed in real time, and M87 can be seen in time lapse, allowing astronomers to glean new details about how matter is drawn into and consumed by a black hole.

EHT researchers are already analyzing data from Sgr A* and M87 at the new frequencies that could be released within the next year. In addition, new observatories may be added to the telescope to make the virtual telescope even stronger; one has already been approved for the Canary Islands, and others are being studied in places like South Africa, Mexico, and Wyoming that can improve upon the work, and draw in more collaborators.

“This really is a remarkable team that’s come together to do this,” Doeleman says. “We rely on engineers [and] dedicated observers around the globe working together to pull off something like this and it’s hats off to the full team for coming together and doing this.”