Seminar and Journal Club

Matias Suazo
February 17, 2022
Zoom recording

Dyson spheres are hypothetical megastructures built by advanced extraterrestrial civilizations to harvest radiation energy from stars. Here, we combine optical data from Gaia DR2 with mid-infrared data from AllWISE to set the strongest upper limits on the prevalence of partial Dyson spheres within the Milky Way. Conservative upper limits are presented on the fraction of stars that may potentially host non-reflective Dyson spheres that absorb up to 90% of the bolometric luminosity of their host stars and emit thermal waste-heat in the 100–1000 K range. In our sample of stars within 100 pc, we find that one over 100000 stars could potentially host ∼ 300 K Dyson spheres at 90% completion. These limits become progressively weaker for less complete Dyson spheres due to increased confusion with naturally occurring sources of strong mid-infrared radiation, and also at larger distances, due to the detection limits of WISE.

Jason Wright
February 10, 2022
Zoom recording

Abstract:
I’ll give an informal overview of a recent paper nearly accepted for publication written with the CATS (Characterizing Atmospheric TechnoSignatures) group, in which we compile and update arguments about the abundance of technological vs. non-technological life in the Galaxy. Despite the intuition propagated by the Drake Equation, there are many plausible reasons that technological life could be more abundant, more detectable, longer lived, and unambiguous than biological life. The implication is that SETI should sit alongside searches for biosignatures as part of an optimum mixed strategy for the detection of life. I’ll also note how both endeavors have explored avenues of the problem the other can benefit from.

Sofia Sheikh
February 3, 2022
Zoom recording

Abstract:
The aim of the search for extraterrestrial intelligence (SETI) is to find technologically-capable life beyond Earth through their technosignatures. On 2019-April-29, the Breakthrough Listen SETI project observed Proxima Centauri with the Parkes “Murriyang” radio telescope. These data contained a narrowband signal with characteristics broadly consistent with a technosignature near 982 MHz (colloquially named ‘blc1’). In this talk, I will present the discovery and characterization of blc1 in the context of the ubiquity of human-generated radio interference. Briefly: we find that blc1 is not an extraterrestrial technosignature, but rather an electronically-drifting intermodulation product of local, time-varying interferers aligned with the observing cadence. We find dozens of instances of radio interference with similar morphologies to blc1 at harmonically-related frequencies to common clock oscillators. These complex intermodulation products highlight the necessity for detailed follow-up of any signal-of-interest. I will end the talk with a discussion of the necessity of signal verification procedures, and lessons learned from this intriguing case study.

Chris House
January 27, 2022

Michael Gillon
January 20, 2022
Zoom recording

Abstract:
Under the hypothesis that self-reproducing probes have formed a galactic-scale communication network by direct Gravitationally-Lensed (GL) links between neighboring systems, we identify Wolf 359, the third nearest stellar system, as an excellent target for a search for alien interstellar communication emitted from our Solar System. Indeed, the Earth is a transiting planet as seen from Wolf 359, meaning that our planet could pass in an alien communication beam once per orbit. We present a first attempt to detect optical messages emitted from the Solar System to this star. While sensitive enough to detect constant emission with emitting power as small as 1W, this search led to a null result. We note that the GL-based interstellar communication method does not necessarily require to emit from the so-called “Solar Gravitational Line” (SGL), starting at ~550 au from the Sun, and that the alien transmitter(s) could be located closer to the Sun and off-center relative to the SGL, at the cost of a smaller but still significant gain compared to a non-GL communication strategy. Basing on this consideration and focusing on the 20 nearest stars, we initiated a search for moving objects whose motion would be consistent with the one of the hypothesized alien transmitters, assuming them to use a solar sail to maintain their radial distance to the Sun. For Wolf 359, we could not reliably identify any such object up to magnitude ~23.5, which corresponds to an explored zone extending as far as Uranus’ orbit (20 au).

Rebecca Charbonneau
December 9, 2021
Zoom Recording

Abstract:
In 1989, the SETI Committee of the International Academy of Astronautics established its first post-detection protocol, the “Declaration of Principles Concerning Activities Following the Detection of Extraterrestrial Intelligence”. The protocol was designed to serve as a guideline for the international scientific community on steps to take after the successful detection of extraterrestrial intelligence.
This talk will examine the protocol as a product of international relations and draw from the early history of SETI to show how Cold War tensions and the first “false alarm” detection in the Soviet Union influenced the development of the protocol.

Macy Huston
December 2, 2021
Zoom Recording

Abstract:
The search for signs of extraterrestrial technology, or technosignatures, includes the search for objects which collect starlight for some technological use, such as those composing a Dyson sphere. These searches typically account for a star’s light and some blackbody temperature for the surrounding structure. However, such a structure inevitably returns some light back to the surface of its star, either from direct reflection or thermal re-emission. Due to their negative gravitothermal heat capacity, irradiated stars expand and cool, particularly in convective regions. In this talk, I will present MESA simulations used to quantify this effect in main sequence stars for a variety of Dyson sphere configurations. I will conclude with a description of when this effect matters observationally and our color-magnitude diagrams generated for a broad range of possible Dyson sphere-star systems.

David Kipping
November 4, 2021
Zoom recording

Abstract
It’s often said that one data point teaches you nothing. In fact, zero data points teaches you nothing, and no magical transition happens from one to two data points. Yet clearly, one data point is the opposite regime to the data-driven enterprise typical of large surveys, where the data is so overwhelming it guides us quite clearly. In this talk, I’ll start by discussing how the Copernican/Mediocrity Principle attempts to exploit one data point with the example concerning the plurality of life, where it flatly fails due to selection bias (and the weak anthropic principle). However, this problem can be recast in terms of timings to make statistical progress, although naturally with a result featuring considerable uncertainty. I will then show how this approach can be extended to the longevity of civilisations. The statistics of one is particularly pertinent for “black swan” events in astronomy, one-offs that often inspire considerable theoretical/observational follow-up – such as Boyajian’s Star or Oumuamua. I’ll present a general Bayesian framework for interpreting such events and demonstrate why black swans require considerable patience to resolve their nature.

James Howell
October 29, 2021
Zoom recording

Abstract:
In the past twenty years, the number of confirmed exoplanets has jumped 150 fold (< 40 before 2000, > 4,800 in 2021) and that total is likely to continue to grow rapidly. Informed efforts to narrow the search for biosignatures and technosignatures to most-likely “habitable zones” are thus increasingly required. Relevant to this goal, there is a long tradition of efforts to build parametric frameworks describing likely scenarios for the necessary sequence of (1) emergence of life, (2) emergence of complex life, and (3) emergence of intelligence leading to technological civilization. These attempts have been guided by biology (e.g. “evolutionary transitions”) or physical and statistical first principles (“hard steps”). Both categories of concepts provide preliminary analytical tools, but both suffer from fundamental conceptual and practical flaws. We will discuss a framework for analysis that proceeds from the contemporary biological consensus on the natural history of this biosphere, and attempts to generalize to (very) different planetary conditions.

Jean-luc Margot
October 21, 2021
Zoom recording

Abstract:
Searches for biosignatures and technosignatures are designed to find evidence of life elsewhere, and it is not clear which strategy will provide unambiguous evidence first. What is clear is that the volume of the Galaxy that can be sampled with a search for radio technosignatures is millions of times larger than the relatively small, local bubble conducive to the search for biosignatures. Since 2016, the UCLA SETI Group has been conducting a search for narrowband radio technosignatures with the largest fully steerable telescope on Earth. We have sampled over 36,000 stars with known parallaxes and detected over 56 million candidate signals. In terms of the number of SNR>10-detections per unit bandwidth per unit integration time, our search is 150-200 times more efficient than some of the recent searches conducted by the Breakthrough Listen team. In 2020, our group was awarded a grant from the NASA Exoplanet Research Program to expand our search and develop a signal injection and recovery analysis tool, which is required to place meaningful upper limits on the prevalence of certain extraterrestrial transmitters. I will describe our algorithms and results to date, including a machine learning application that reduces the number of candidate signals that require human evaluation by a factor of ~16. Our search has been tightly coupled to the annual UCLA SETI course, which is perhaps the first full-length SETI course in a university setting, and which has exposed 100+ undergraduate students and 10+ graduate students to SETI science in six offerings since 2016.