In a recent study published in The Astronomical Journal, a researcher from the École Polytechnique Fédérale de Lausanne (EPFL) discusses the potential reasons why we haven’t received technoemission, also called technosignatures, from an extraterrestrial intelligence during the 60 years that SETI has been searching, along with recommending additional methods as to how we can continue to search for such emissions.
Dr. Claudio Grimaldi, who is a guest scientist at the Laboratory of Statistical Biophysics at EPFL and sole author of the study, suggests that Earth has not received a technoemission simply because Earth could be in what he refers to as a “void space”, meaning the area of space that Earth resides in has been devoid of technoemissions.
Image of radio telescopes at the Karl G. Jansky Very Large Array near Socorro, New Mexico, scanning the heavens for extraterrestrial technoemissions. (Credit: Jeff Hellermann/National Radio Astronomy Observatory/Associated Universities, Inc./National Science Foundation)
“If it is true that we’ve been in a void region for sixty years, our model suggests that there are less than one to five electromagnetic emissions per century anywhere in our galaxy. This would make them about as rare as supernovas in the Milky Way,” said Dr. Grimaldi.
For the study, Dr. Grimaldi developed a model that assumed the existence of technological “emitters” of extraterrestrial origin that are constantly broadcasting emissions and are equally dispersed throughout our Milky Way Galaxy. In the end, Dr. Grimaldi came up with three viewpoints of optimism regarding how long until Earth will detect a technoemission, which he refers to as a “crossing event”: an optimistic timeframe of 60 years from now, a moderately optimistic timeframe of 170 years from now, and a marginally optimistic timeframe of 1800 years from now.
Image of the Allen Telescope Array in Hat Creek, CA, scanning the skies for signals from extraterrestrial civilizations. (Credit: Seth Shostak/SETI Institute)
The study concludes by emphasizing the ideas presented could be either true or false but suggested that hunting for technoemissions should go beyond SETI searches while focusing on more “commensal investigations, i.e., searching for technosignals from data collected by telescopes performing other observational activities, rather than investing telescope time in active SETI searches.”
One such option is the privately funded Breakthrough Listen project that is conducting the most extensive search for technoemissions to date, which was started in 2015 and is slated to run until 2025. Using radio telescopes that whose sensitivity is 50 times greater than current telescopes committed to searching for extraterrestrial intelligence, Breakthrough Listen is surveying 1,000,000 of the Earth’s closest stars, along with scanning the center of the Milky Way and what’s known as the galactic plane. The search even scans for emissions from 100 of the Milky Way’s closest galaxies. This study also comes as exoplanets are being discovered almost daily and over 5,300 have been confirmed as of this writing.
Learn more about how Breakthrough Listen tried to detect technosignatures from 12 exoplanets in 2022.
Dr. Grimaldi emphasizes that “the truth is, we don’t know where to search, at which frequencies and wavelengths. We are currently looking at other phenomena using our telescopes, so the best strategy might be to adopt the SETI community’s past approach of using data from other astrophysical studies – detecting radio emissions from other stars or galaxies – to see if they contain any techno-signals and make that the standard practice.
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When Black Holes Merge, They’ll Ring Like a Bell
When two black holes collide, they don’t smash into each other the way two stars might. A black hole is an intensely curved region of space that can be described by only its mass, rotation, and electric charge, so two black holes release violent gravitational ripples as merge into a single black hole. The new black hole continues to emit gravitational waves until it settles down into a simple rotating black hole. That settling down period is known as the ring down, and its pattern holds clues to some of the deepest mysteries of gravitational physics.
Gravitational wave observatories such as the Laser Interferometry Gravitational-Wave Observatory (LIGO) have mostly focused on the inspiral period of black hole mergers. This is the period where the two black holes orbit ever closer to each other, creating a rhythmic stream of strong gravitational waves. From this astronomers can determine the mass and rotation of the original black holes, as well as the mass and rotation of the merged black hole. The pattern of gravitational waves we observe is governed by Einstein’s general relativity equations, and by matching observation to theory we learn about black holes.
General relativity describes gravity extremely well. Of all the gravitational tests we’ve done, they all agree with general relativity. But Einstein’s theory doesn’t play well with the other extremely accurate physical theory, quantum mechanics. Because of this, physicists have proposed modifications to general relativity that are more compatible with quantum theory. Under these modified theories, there are subtle differences in the way merged black holes ring down, but observing those differences hasn’t been possible. But a couple of new studies show how we might be able to observe them in the next LIGO run.
The modified Teukolsky equation. Credit: Li, Dongjun, et al
In the first work, the team focused on what is known as the Teukolsky Equation. First proposed by Saul Teukolsky, the equations are an efficient way of analyzing gravitational waves. The equations only apply to classical general relativity, so the team developed a way to modify the equations for modified general relativity models. Since the solutions to both the Teukolsky and modified Teukolsky equations don’t require a massive supercomputer to solve, the team can compare black hole ring downs in various gravitational models.
The second work looks at how this would be done with LIGO data. Rather than focusing on general differences, this work focuses on what is known as the no-hair theorem. General relativity predicts that no matter how two black holes merge, the final merged black hole must be described by only mass, rotation, and charge. It can’t have any “hair”, or remnant features of the collision. In some modified versions of general relativity, black holes can have certain features, which would violate the no-hair theorem. In this second work, the authors show how this could be used to test general relativity against certain modified theories.
LIGO has just begun its latest observation run, so it will be a while before there is enough data to test. But we may soon have a new observational test of Einstein’s old theory, and we might just prove it isn’t the final theory of gravity after all.
Reference: Li, Dongjun, et al. “Perturbations of spinning black holes beyond General Relativity: Modified Teukolsky equation.” Physical Review X 13.2 (2022): 021029.
Reference: Ma, Sizheng, Ling Sun, and Yanbei Chen. “Black hole spectroscopy by mode cleaning.” Physical Review Letters 130.2 (2023): 141401.
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There’s a Polar Cyclone on Uranus’ North Pole
Uranus takes 84 years to orbit the Sun, and so that last time that planet’s north polar region was pointed at Earth, radio telescope technology was in its infancy.
But now, scientists have been using radio telescopes like the Very Large Array (VLA) the past few years as Uranus has slowly revealing more and more of its north pole. VLA microwave observations from 2021 and 2022 show a giant cyclone swirling around this region, with a bright, compact spot centered at Uranus’ pole. Data also reveals patterns in temperature, zonal wind speed and trace gas variations consistent with a polar cyclone.
Uranus as seen by NASA’s Voyager 2. Credit: NASA/JPL
Scientists have long known that Uranus’ south pole has a swirling feature. When Voyager 2 flew past Uranus in 1986, it detected high wind speeds there. However, the way the planet was tilted did not allow Voyager to see the north pole.
But the VLA in New Mexico has now been studying Uranus the past several years, and observations collected in 2015, 2021, and 2022 were able to peer deep into Uranus’ atmosphere. The thermal emission data showed that circulating air at the north pole seems to be warmer and drier, which are the hallmarks of a strong cyclone.
“These observations tell us a lot more about the story of Uranus. It’s a much more dynamic world than you might think,” said Alex Akins of NASA’s Jet Propulsion Laboratory in Southern California, who is lead author of a new study published in Geophysical Letters. “It isn’t just a plain blue ball of gas. There’s a lot happening under the hood.”
The researchers said the cyclone on Uranus is similar to the polar cyclones observed by the Cassini mission at Saturn. With the new findings, cyclones (which rotate in the same direction their planet rotates) or anti-cyclones (which rotate in the opposite direction) have now been identified at the poles on every planet in our solar system that has an atmosphere. The researchers said this confirms a broad truth that planets with substantial atmospheres – whether the worlds are made of rock or gas – all show signs of swirling vortexes at the poles.
Uranus’ north pole is now in springtime. As it continues into summer, astronomers hope to see even more changes in its atmosphere.
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