Seminar and Journal Club

Matías Suazo
December 7, 2023
Zoom recording

Abstract:
The quest for finding intelligent extraterrestrial life has captivated humanity for a long time, and various strategies have been developed to search for signs of advanced civilizations. One approach involves looking for indirect evidence of extraterrestrial technology, such as Dyson spheres, hypothetical megastructures constructed by advanced civilizations that would encompass a star to harness its energy. This structure would potentially emit detectable waste heat infrared radiation. Missions such as Gaia, 2MASS, and WISE provide extensive observations that can be utilized to identify the potential observational signatures of Dyson spheres, which include optical dimming and an infrared excess. In this talk, we present a pipeline to gather sources that exhibit unusual infrared radiation not easily attributable to known astronomical sources and compatible with our Dyson sphere models. We present our top candidates and, in a few cases, optical spectroscopy. Finally, we discuss potential explanations for the infrared excess.

Sara Seager
November 16, 2023
Zoom recording

Abstract:
Waste gas products from technological civilizations may accumulate in an exoplanet atmosphere to detectable levels. We propose nitrogen trifluoride (NF3) and sulfur hexafluoride (SF6) as ideal technosignature gases. Earth life avoids producing or using any N-F or S-F bond-containing molecules and makes no fully fluorinated molecules with any element. NF3 and SF6 may be universal technosignatures owing to their special industrial properties, which unlike biosignature gases, are not species-dependent. Other key relevant qualities of NF3 and SF6 are: their extremely low water solubility, unique spectral features, and long atmospheric lifetimes. NF3 has no non-human sources and was absent from Earth’s pre-industrial atmosphere. SF6 is released in only tiny amounts from fluorine-containing minerals, and is likely produced in only trivial amounts by volcanic eruptions. We propose a strategy to rule out SF6’s abiotic source by simultaneous observations of SiF4, which is released by volcanoes in an order of magnitude higher abundance than SF6. Other fully fluorinated human-made molecules are of interest, but their chemical and spectral properties are unavailable. We summarize why life on Earth—and perhaps life elsewhere—avoids using F. We caution, however, that we cannot definitively disentangle an alien biochemistry byproduct from a technosignature gas.

Nick Tusay
November 9, 2023
Zoom recording

Abstract:
The newly refurbished The Allen Telescope Array uses beam-forming within its primary field of view for SETI observations in an effort to discriminate between local radio frequency interference (RFI) and signals localized to the target source. In late October and early November, 2022, 28 hours of observations of the TRAPPIST-1 system were taken and preprocessed in this mode. After processing the filterbank data products with turboSETI’s deDoppler algorithm to identify signals, a new pipeline was created and implemented to handle RFI filtering for this and other high frequency resolution multi-beam observations. This talk will be a look at the methods employed by this pipeline, including identical signal rejection, power correlation, signal to noise calculation, and signal attenuation, and some preliminary results.

Jason Wright
November 2, 2023
Zoom recording

Abstract:
I apply the thermodynamics of radiation to Dyson spheres as machines that do work or computation, and examine their observational consequences. I identify four properties of Dyson spheres that complicate typical analyses: globally, they may do no work in the usual sense; they use radiation as the source and sink of energy; they accept radiation from a limited range of solid angle; and they conserve energy flux globally. I consider three kinds of activities: computation at the Landauer limit; dissipative activities, in which the energy of a sphere’s activities cascades into waste heat, as for a biosphere; and “traditional” work that leaves the sphere, such as radio emission. I apply the Landsberg formalism to derive efficiency limits in all 3 cases, and show that optical circulators provide an “existence proof” that greatly simplifies the problem and allows the Landsberg limit to be plausibly approached. I find that for computation and traditional work, there is little to no advantage to nesting shells (as in a “Matrioshka Brain”); that the optimal use of mass is generally to make very small and hot Dyson spheres; that for “complete” Dyson spheres we expect optical depths of several; and that in all cases the Landsberg limit corresponds to a form of the Carnot limit. I explore how these conclusions might change in the face of complications such as the sphere having practical efficiencies below the Landsberg limit (using the endoreversible limit as an example); no use of optical circulators; and swarms of materials instead of shells.

Chenoa Tremblay
October 19, 2023
Zoom recording

Abstract:
Within the fields of astrobiology, planetary science, and radio astronomy there are teams around the world constantly looking for signs that life exists on other planets than Earth. The search for complex life through technosignatures, observational manifestations of technology, aims to constrain the prevalence and distribution of potential of technologically advanced life in the Universe. Significant advances in real-time data analysis, driven by the reduced costs of computation, have led to the development of the Commensal Open-Source Multimode Interferometer Cluster (COSMIC) on the Karl G. Jansky Very Large Array (VLA) in New Mexico, USA. As such we are performing one of the largest technosignature surveys of all time with a real-time and autonomous workflow. In this presentation, I will provide an overview of COSMIC, where it sits in the landscape of technosignature searches, and what we have learned in the first 6 months of commensal observing with the VLA as well as some of our first results.

Julia DeMarines
October 5, 2023
Zoom recording

Abstract:
The Moonbounce Project is a pet name for an observing campaign that observed the moon for eight nights with the Green Bank Telescope in late 2019 with the goal of empirically measuring Earth’s techosignature in radio frequencies via reflected terrestrial radio light. This presentation will discuss the science and results of these observations and discuss their implications for future SETI searches.

Megan Grace Li
September 28, 2023
Zoom recording

Abstract:
UCLA SETI is conducting a search for narrowband radio technosignatures in collaboration with UCLA students and volunteers from the general public. Our search uses the L-Band Receiver of the Green Bank Telescope, which spans (1.15–1.73 GHz). From its conception in 2016, UCLA SETI has viewed over 50,000 stars and reviewed over 77 million candidate signals, all of which are concluded to be radio frequency interference. Each Spring, UCLA SETI hosts the UCLA SETI course, where undergraduate and graduate students of various disciplines are invited to contribute to our search. Additionally, this year, UCLA SETI launched “Are we alone in the universe?”, a citizen science collaboration hosted by Zooniverse. Through this platform, volunteers recognize and classify various forms of radio frequency interference. The signals that are classified on Zooniverse have been pre-selected out of ~77 million candidate signals as the most likely to be generated by extraterrestrials. Funded by NASA, The Planetary Society, and generous donors, “Are we alone in the universe?” has already inspired over 12,000 volunteers who have collectively submitted over 380,000 classifications. Along with results from our volunteers, we are excited to present a signal injection and recovery analysis, a modified figure of merit (inspired by the Drake figure of merit), a formalism for existence limits, and the detection of signals from Ma, et al. (2023) without the use of AI.

Bryan Brzycki
September 21, 2023
Zoom recording

Abstract:
To date, the search for radio technosignatures has focused on sky location as a primary discriminant between technosignature candidates and anthropogenic radio frequency interference (RFI). We present our investigation on the possibility of searching for technosignatures by identifying the presence and nature of intensity scintillations arising from the turbulent, ionized plasma of the interstellar medium (ISM). Past works have detailed how interstellar scattering can both enhance and diminish the detectability of narrowband radio signals. We use the NE2001 Galactic free electron density model to estimate scintillation timescales to which narrowband signal searches would be sensitive, and discuss ways in which we might practically detect strong intensity scintillations in detected signals. We further analyze the RFI environment of the Robert C. Byrd Green Bank Telescope (GBT) with the proposed methodology and comment on the feasibility of using scintillation as a filter for technosignature candidates.

Darryl Seligman
September 14, 2023
Zoom recording

Abstract:
1I/‘Oumuamua was the first macroscopic interstellar object discovered traversing the inner Solar System. In this talk, I will review the mysterious properties that 1I/‘Oumuamua exhibited, including an elongated shape and a surprisingly low velocity with respect to the local standard of rest. Most intriguing, 1I/‘Oumuamua appeared unresolved and asteroid-like, yet moved under the action of nongravitational acceleration. I will discuss existing theories regarding the physical nature of the object that have invoked both artificial and natural provenances. This context helps to delineate the criteria for identifying natural behavior as opposed to technosignatures. The interstellar interlopers and their divergent properties provide our only window so far onto an enormous and previously unknown galactic population. The forthcoming Rubin Observatory Legacy Survey of Space and Time (LSST) is poised to further transform our understanding of interstellar interlopers, and I will discuss the feasibility of future discoveries via ground-based observations as well as possible intercept missions.

Bárbara Cabrales
September 7, 2023
Zoom recording

Abstract:
The SETI Ellipsoid is a strategy for technosignature candidate selection which assumes that extraterrestrial civilizations have observed a common, galactic-scale event and may use it as a Schelling point to broadcast synchronized signals indicating their presence. The idea of synchronizing technosignature searches with astronomical events has been present in the literature since the 70s, but our distance estimates to stars have historically been too imprecise for this technique. New distances from Gaia make finding targets on a SETI Ellipsoid possible and have allowed for the method to be used on different astronomical events, collaboratively with other surveys, in real-time and archivally, all in the past couple of years. We present an overview of recent developments within the SETI field related to the Ellipsoid method.