Scientists working with the Event Horizon Telescope recently released an image of the supermassive black hole at the center of our galaxy, the first-ever picture of our local singularity. Named Sagittarius A* (pronounced “A star”), the black hole has the mass of four million suns, and is surrounded by a vortex of glowing material heated to extreme temperatures as it’s sucked into the unknown world of the black hole.
The picture is just the second black hole to be imaged, following the release in 2019 of a picture of the black hole at the center of the galaxy M87. These stunning snapshots come thanks to the EHT, which is not one telescope but many spread out across the planet. Combining these observations lets astronomers effectively create a telescope that is as large as Earth, and which can see objects much farther away than anything else. For scale, consider that the EHT is powerful enough that from Earth it could see an orange placed on the Moon.
Peering inside a black hole for the first time is an undeniably important achievement, and one that captured the imaginations of astronomers and the public alike. But with the world’s most powerful telescope, surely there are other cool things to find out there in the universe — like, say, extraterrestrial intelligence. Could we turn the EHT on distant planets, using its superior resolution to spy on potential alien civilizations?
Why that probably won’t work
It sounds like an amazing idea, but, unfortunately, the EHT isn’t really right for the search for extraterrestrial intelligence (SETI), says Cherry Ng, a radio astronomer working with the Breakthrough Listen SETI project.
“When it comes to SETI research, our primary goal is in finding a signal,” Ng says in an email to Inverse. For that, the EHT is, ironically, too powerful.
Most SETI research involves looking at broad swathes of the night sky to search for signals that look like they may have come from intelligent beings. These kinds of surveys don’t zoom in on things like the EHT does, but they can cover a lot of space quickly. And with trillions of stars out there, covering a lot of space is crucial.
Pointing the EHT at even the roughly 5,000 known exoplanets for ten minutes each would take 36 days of continuous observing, estimates Chenoa Tremblay, a researcher at the SETI Institute. And that’s not even accounting for telescope downtime, calibration, and aiming.
The EHT as an organization is not very well set up to chase down every hint of ET, says Sofia Sheikh, a postdoctoral researcher at the University of California, Berkeley’s SETI Research Center.
“The EHT is a collaboration between many different telescopes around the world,” Sheikh says in an email to Inverse. “Getting coordinated observations with them all is expensive and time-consuming, and we'd have to have a really good argument to access that level of resources for SETI.”
The EHT is also optimized to collect data in a very specific wavelength: 1.3 millimeters. Radio waves at this frequency can travel through the clouds of hot gas surrounding a black hole, allowing us to peer inside to get a clear image. These wavelengths are nearly as short as radio waves get, something that’s crucial for getting high-resolution images.
But ET would need to be broadcasting signals at that very specific wavelength, says Dan Werthimer, an astronomer at the University of California, Berkeley. Astronomers looking for extraterrestrial intelligence do look for radio waves, but they tend to look for signals at much longer wavelengths, similar to those we use on Earth for communication.
What is a planet-size telescope good for?
Where the EHT could potentially come into play in SETI would be if we had already found a signal and wanted to zoom in on it, Sheikh says. Assuming the signal happened to include the 1.3-millimeter wavelength, and we had a good idea of where it was coming from, astronomers could follow up on an interesting signal with the EHT to learn more about where it came from.
If a signal was coming from a transmitter on a planet orbiting a star, for example, “we could see the planet go around the star, we could see the transmitter orbit the star,” Werthimer says. “We could actually see that even if you were on the other side of the galaxy, with the resolution of the EHT.”
The EHT might also be good for finding something like a cool Dyson sphere, Sheikh says. These are hypothetical structures, first proposed by the physicist Freeman Dyson, built around entire stars that capture most or all of the energy from them. It’s something an advanced civilization might build to meet its massive energy needs.
Most Dyson spheres would radiate most of their energy in the infrared, at higher frequencies than radio waves. But one that’s much cooler, and therefore releases energy at lower frequencies, might be observable by the EHT.
Still, that eventuality is fairly unlikely. But astronomers are already using telescopes like the EHT to carry out SETI research at wavelengths where we’re more likely to actually see something. The EHT is just one example of what astronomers call very long baseline interferometry (VLBI), which means using multiple telescopes spread out from each other.
There are a number of projects around the world that use multiple spaced out telescopes to find things in the universe (though none are as big as the EHT). The Very Large Array (VLA), in New Mexico, for example, consists of 27 radio antennas that can be moved as much as 23 miles apart from each to search for events such as radio waves from clouds of gas in our galaxy or plasma emitted from black holes. Similarly, the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope is made of 66 radio antennae spread across Chile’s Atacama desert. And other telescope arrays keeping tabs on signals in a range of wavelengths can be found in Australia, South Africa, and elsewhere.
These kinds of telescopes consisting of multiple receivers working together are called interferometers, and they’re crucial for SETI research. The signals scientists think we might find from aliens, called technosignatures, look very similar to the kinds of signals being emitted from all over Earth today.
“There are a lot of radio signals on Earth, we call it radio frequency interference, or radiofrequency pollution,” Werthimer says. “This false alarm problem is getting worse and worse … it’s getting harder and harder to do SETI from the Earth.”
Using multiple receivers, however, lets scientists distinguish signals from Earth from those that come from much farther away. That’s where interferometers like the VLA come in, helping astronomers peer beyond Earthly interference. Future telescopes, like the planned next-generation Very Large Array (ngVLA) will be even bigger, and should give astronomers an even better look at far-away radio signals. That means we’re better equipped than ever before to find potential signals of extraterrestrial intelligence in the universe, and to follow up on them should one appear.
As for the EHT, it’s been busy in the past few years adding new telescopes to the array, and following up on its black hole observations. Future plans include the addition of even more telescopes and increasingly detailed observations of black holes, potentially even including video imagery. And maybe, just maybe, being called into action to take a picture of aliens.