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 image of our local singularity. Named Sagittarius A* (pronounced “Star A”), the black hole has the mass of four million suns and is surrounded by a vortex of glowing matter heated to extreme temperatures as it is sucked into the hole’s unknown world. black.
The image is only the second black hole to be photographed, following the release in 2019 of an image of the black hole at the center of the M87 galaxy. These stunning snapshots are courtesy of the EHT, which is not one telescope but several scattered across the planet. Combining these observations allows astronomers to effectively create a telescope as big as Earth that can see objects much farther than anything else. For scale, consider the EHT to be powerful enough that from Earth it could see an orange placed on the Moon.
Looking inside a black hole for the first time is an undeniably significant achievement, one that has captured the imagination of astronomers and the public. But with the most powerful telescope in the world, there are sure to be other interesting things to discover in the universe – like, say, extraterrestrial intelligence. Could we shoot the EHT on distant planets, using its superior resolution to spy on potential extraterrestrial civilizations?
Why it probably won’t work
It sounds like an amazing idea, but, unfortunately, EHT isn’t really suitable 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 main goal is to find a signal,” Ng said in an email to Reverse. For that, the EHT is, ironically, too powerful.
Most SETI research involves scanning large swaths of the night sky for signals that appear to be coming from intelligent beings. These types 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 the roughly 5,000 known exoplanets for ten minutes each would take 36 days of continuous observation, estimates Chenoa Tremblay, a researcher at the SETI Institute. And that’s not even taking into account downtime, calibration, and aiming the telescope.
The EHT as an organization is not very well organized to drive out any suspicion of ET, says Sofia Sheikh, postdoctoral researcher at the University of California, Berkeley SETI Research Center.
“The EHT is a collaboration between many different telescopes around the world,” Sheikh said in an email to Reverse. “Getting coordinated observations with all of them is expensive and time-consuming, and we would need 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 look inside to get a clear picture. These wavelengths are almost as short as radio waves, which is crucial for obtaining high resolution images.
But ET should broadcast signals at this very specific wavelength, says Dan Werthimer, an astronomer at the University of California, Berkeley. Astronomers looking for extraterrestrial intelligence 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 telescope the size of a planet used for?
Where EHT could potentially come into play in SETI would be if we had already found a signal and wanted to zoom in on it, says Sheikh. Assuming the signal included the 1.3 millimeter wavelength and we had a good idea of where it came from, astronomers could track an interesting signal with the EHT to learn more about where it came from.
If a signal came from a transmitter on a planet orbiting a star, for example, “we could see the planet orbiting the star, we could see the transmitter orbiting the star”, explains Werthimer. “We could actually see this even if you were on the other side of the galaxy, with the resolution of the EHT.”
The EHT could also be useful for finding something like a cool Dyson sphere, says Sheikh. They are hypothetical structures, first proposed by physicist Freeman Dyson, built around whole stars that capture most or all of their energy. It is something that an advanced civilization could build to meet its enormous energy needs.
Most Dyson spheres would radiate most of their energy in infrared, at frequencies higher than radio waves. But one that is much colder, and therefore releases energy at lower frequencies, could be observable by the EHT.
However, this eventuality is quite unlikely. But astronomers are already using telescopes like the EHT to do SETI searches at wavelengths where we’re more likely to see something. The EHT is just one example of what astronomers call very long baseline interferometry (VLBI), meaning the use of multiple spaced apart telescopes.
There are a number of projects around the world that use multiple spaced apart telescopes to find objects in the universe (although none as large as the EHT). The Very large painting (VLA) in New Mexico, for example, consists of 27 radio antennas that can be moved up to 23 miles apart to search for events such as radio waves from clouds of gas in our galaxy or the plasma emitted by black holes. Likewise, the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope is made up of 66 radio antennas spread across the Atacama Desert in Chile. And other telescope arrays keeping an eye on signals in a range of wavelengths can be found in Australia, South Africa and elsewhere.
These types of telescopes made up of multiple receivers working together are called interferometers, and they are crucial for SETI research. The signals that scientists think we might find from extraterrestrials, called technosignatures, are very similar to the types of signals emitted from all over Earth today.
“There are a lot of radio signals on Earth, we call it radio interference or radio frequency pollution,” says Werthimer. “This false alarm problem is getting worse and worse… it’s getting harder and harder to do SETI from Earth.”
Using multiple receivers, however, allows scientists to distinguish signals from Earth from those that come from much further away. This is where interferometers like the VLA come in, helping astronomers observe beyond terrestrial interference. Future telescopes, as planned Next generation Very Large Array (ngVLA) will be even larger and should give astronomers better insight into distant radio signals. This means that we are better equipped than ever to find potential signals of extraterrestrial intelligence in the universe, and to track them if one appears.
As for the EHT, it has been busy in recent years adding new telescopes to the network and keeping up with its black hole observations. Future plans include adding even more telescopes and increasingly detailed observations of black holes, potentially including even video images. And maybe, just maybe, get called into action to take a picture of aliens.