Search

The discovery of ubiquitous habitable extrasolar planets, combined with revolutionary advances in instrumentation and observational capabilities, has ushered in a renaissance in the search for extra-terrestrial intelligence (SETI). Large scale SETI activities are now underway at numerous international facilities. The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the largest single-aperture radio telescope in the world, well positioned to conduct sensitive searches for radio emission indicative of exo-intelligence. SETI is one of the five key science goals specified in the original FAST project plan. A collaboration with the Breakthrough Listen Initiative has been initiated in 2016 with a joint statement signed both by Dr. Jun Yan, the then director of the National Astronomical Observatories, Chinese Academy of Sciences (NAOC), and Dr. Peter Worden, the Chairman of the Breakthrough Prize Foundation. In this paper, we highlight some of the unique features of FAST that will allow for novel SETI observations. We identify and describe three different signal types indicative of a technological source, namely, narrow-band, wide-band artificially dispersed, and modulated signals. We here propose observations with FAST to achieve sensitivities never before explored., Comment: 14 pages, 8 figures, Accepted by Research in Astron. Astrophys. (FAST special issue)

We analyze the potential transit light curve effects due to a Clarke belt of satellites around an exoplanet. Building on code and analysis from Korpela, Sallmen, & Leystra Greene (2015), we refine the transit analysis of Socas-Navarro (2018) by incorporating limb-darkening and taking an observer-centered approach to examining residuals. These considerations make Clarke exobelt detectability more difficult than previous estimates. We also consider practical dynamical issues for exobelts, confirming that synchronously orbiting belts are dynamically unstable around planets in the habitable zones of M stars, and determining the maximum quasi-stable belt size in these situations. Using simulations for both G and M stars, we conclude that to have an even marginally detectable impact on transit light curves, exobelts must be substantially denser than previous estimates. We also estimate collision rates for the required satellite densities assuming random orbits, and find they would present significant monitoring and guidance challenges. If detectable belts exist, they would require some (possibly high) degree of ordering to avoid collisions, and must be actively maintained or they will dissipate on relatively short astronomical timescales. We conclude that detectable exobelts are likely to be rare, and have extremely low prospects for detection by transit monitoring from both current and upcoming missions., Comment: Accepted by The Astronomical Journal. Incorporates feedback from referee. 17 pages including 5 figures

Breakthrough Listen is the most comprehensive and sensitive search for extraterrestrial intelligence (SETI) to date, employing a collection of international observational facilities including both radio and optical telescopes. During the first three years of the Listen program, thousands of targets have been observed with the Green Bank Telescope (GBT), Parkes Telescope and Automated Planet Finder. At GBT and Parkes, observations have been performed ranging from 700 MHz to 26 GHz, with raw data volumes averaging over 1PB / day. A pseudo-real time software spectroscopy suite is used to produce multi-resolution spectrograms amounting to approximately 400 GB hr^-1 GHz^-1 beam^-1. For certain targets, raw baseband voltage data is also preserved. Observations with the Automated Planet Finder produce both 2-dimensional and 1-dimensional high resolution (R~10^5) echelle spectral data. Although the primary purpose of Listen data acquisition is for SETI, a range of secondary science has also been performed with these data, including studies of fast radio bursts. Other current and potential research topics include spectral line studies, searches for certain kinds of dark matter, probes of interstellar scattering, pulsar searches, radio transient searches and investigations of stellar activity. Listen data are also being used in the development of algorithms, including machine learning approaches to modulation scheme classification and outlier detection, that have wide applicability not just for astronomical research but for a broad range of science and engineering. In this paper, we describe the hardware and software pipeline used for collection, reduction, archival, and public dissemination of Listen data. We describe the data formats and tools, and present Breakthrough Listen Data Release 1.0 (BLDR 1.0), a defined set of publicly-available raw and reduced data totalling 1 PB., Comment: 28 pages, 15 figures, PASP accepted

Advancing the scientific frontier in the search for life in the universe requires support of searches for both biosignatures and technosignatures. A modest budgetary increment can expand the search for life in the universe from primitive to complex life and from the solar neighborhood to the entire Galaxy., Comment: 8 pages, 2 figures, science white paper submitted to the Astro2020 decadal survey on Astronomy and Astrophysics

Neutral atomic hydrogen (HI) gas in interstellar space is largely organized into filaments, loops, and shells, the most prominent of which are "supershells". These gigantic structures requiring $\gtrsim 3 \times 10^{52}$ erg to form are generally thought to be produced by either the explosion of multiple supernovae (SNe) in OB associations or alternatively by the impact of high-velocity clouds (HVCs) falling to the Galactic disk. Here we report the detection of a kiloparsec (kpc)-size supershell in the outskirts of the Milky Way with the compact HVC 040+01$-$282 (hereafter CHVC040) at its geometrical center using the "Inner-Galaxy Arecibo L-band Feed Array" HI 21-cm survey data. The morphological and physical properties of both objects suggest that CHVC040, which is either a fragment of a nearby disrupted galaxy or a cloud originated from an intergalactic accreting flow, collided with the disk $\sim 5$ Myrs ago to form the supershell. Our result shows that some compact HVCs can survive their trip through the Galactic halo and inject energy and momentum into the Milky Way disk., Comment: 10 pages, 5 figures, Accepted for publication in the Astrophysical Journal Letters on July 26, 2016

Galactic HI (neutral hydrogen) shells are central to our understanding of the interstellar medium (ISM), which plays a key role in the development and evolution of galaxies, including our own. Several models involving supernovae and stellar winds have contributed to our broad understanding, but a complete, detailed picture remains elusive. To extend existing Galactic shell catalogs, we visually examined the SETHI (Search for Extraterrestrial HI) database to identify shell-like structures. This high-sensitivity 21-cm radio survey covering the Arecibo sky uniquely provides high-resolution data on shells at a wide range of Galactic latitudes. We present basic information (location, radial velocity, angular size, shape) for 74 previously unidentified HI shells. Due to limitations of coverage and data quality, and the biases inherent in search techniques, our catalog is not a complete sample of Galactic shells. We discuss the catalog completeness, and comment on the new shells' relationship with known interstellar structure as warranted. Unlike many previous catalogs, this sample is not biased towards expanding shells. Where possible we also estimate the kinematic distances, physical sizes, expansion velocities, and energies of these shells. Overall, they are relatively large and old, each the result of multiple supernovae. Unlike previous surveys, we do not find that the shells in our sample are preferentially aligned relative to the Galactic plane., Comment: 17 pages, 7 figures, 6 tables, Published in The Astronomical Journal. This revised version fixes typographical error in equation in third paragraph of Section 6.2

We analyze potential effects of an extraterrestrial civilization's use of orbiting mirrors to illuminate the dark side of a synchronously rotating planet on planetary transit light curves. Previous efforts to detect civilizations based on side effects of planetary-scale engineering have focused on structures affecting the host star output (e.g. Dyson spheres). However, younger civilizations are likely to be less advanced in their engineering efforts, yet still capable of sending small spacecraft into orbit. Since M dwarfs are the most common type of star in the solar neighborhood, it seems plausible that many of the nearest habitable planets orbit dim, low-mass M stars, and will be in synchronous rotation. Logically, a civilization evolving on such a planet may be inspired to illuminate their planet's dark side by placing a single large mirror at the L2 Lagrangian point, or launching a fleet of small thin mirrors into planetary orbit. We briefly examine the requirements and engineering challenges of such a collection of orbiting mirrors, then explore their impact on transit light curves. We incorporate stellar limb darkening and model a simplistic mirror fleet's effects for transits of Earth-like (R = 0.5 to 2 R_Earth) planets which would be synchronously rotating for orbits within the habitable zone of their host star. Although such an installation is undetectable in Kepler data, JWST will provide the sensitivity necessary to detect a fleet of mirrors orbiting Earth-like habitable planets around nearby stars., Comment: 14 pages, 12 figures, some color, rev 3 corrects arithmetic error in cost of launching a mirror fleet