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Our Sky Now And Then: Searches For Lost Stars And Impossible Effects As Probes Of Advanced Extraterrestrial Civilizations
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Theoretical Astrophysics.
2016 (English)In: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 152, no 3, 76Article in journal (Refereed) Published
Abstract [en]

Searches for extraterrestrial intelligence using large survey data often look for possible signatures of astroengineering. We propose searching for physically impossible effects caused by highly advanced technology by carrying out a search for disappearing galaxies and Milky Way stars. We select similar to 10 million objects from USNO-B1.0 with low proper motions (mu < 20 mas yr(-1)) imaged on the sky in two epochs. We search for objects not found at the expected positions in the Sloan Digital Sky Survey (SDSS) by visually examining images of similar to 290,000 USNO-B1.0 objects with no counterpart in the SDSS. We identify some spurious targets in the USNO-B1.0. We find one candidate of interest for follow-up photometry, although it is very uncertain. If the candidate eventually is found, it defines the probability of observing a disappearing-object event in the last decade to less than one in one million in the given samples. Nevertheless, because the complete USNO-B1.0 data. set is 100 times larger than any of our samples, we propose an easily accessible citizen science project in search of USNO-B1.0 objects that have disappeared from the SDSS.

Place, publisher, year, edition, pages
2016. Vol. 152, no 3, 76
Keyword [en]
astrobiology, extraterrestrial intelligence, surveys
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:uu:diva-305484DOI: 10.3847/0004-6256/152/3/76ISI: 000383804300024OAI: oai:DiVA.org:uu-305484DiVA: diva2:1038511
Available from: 2016-10-18 Created: 2016-10-18 Last updated: 2016-11-24Bibliographically approved
In thesis
1. Active Galactic Nuclei in galaxy surveys: Empirical paths to the fiery hearts of cosmic beasts
Open this publication in new window or tab >>Active Galactic Nuclei in galaxy surveys: Empirical paths to the fiery hearts of cosmic beasts
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Some galaxies emit excessive amounts of light from their centers, caused by accretion of gas onto super-massive black holes (SMBH). These galactic cores are often referred to as Active Galactic Nuclei (AGN) and they come in many different forms, distinguishable by their emission properties. The AGN classes fall into two major categories: those with narrow Balmer lines, and those with broad Balmer lines. The AGN Unification theory of radio-quiet AGN predicts the two classes to differ mainly in the viewing angle of the observer who may, or may not, see the central engine due to dust obscuration in the foreground.

In this PhD thesis, I explore the limits of the radio-quiet AGN Unification. In its most famous and simple form, the obscurer is a parsec-sized dust doughnut surrounding the accretion disk. I show that the galaxy neighbours to the two types of AGN are different, in disagreement with the simplest form of unification (Paper I). The two AGN classes differ in their [OIII]5007 luminosity, as well as in their star-formation history (Paper II), suggesting that we must incorporate galactic dust into the concept of AGN Unification, as well as differences in the luminosity of the central engine. I also present a novel, data-driven method to pinpoint the relative spatial origin of certain emission lines in AGN (Paper III). Finally, we conclude the thesis by discussing an anti-transient survey targeted at finding signatures of extra-terrestrial intelligence (Paper IV). This survey can, as a side effect, also be useful to find extreme, variable AGN that challenge both AGN Unification and evolutionary theories.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 47 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1458
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Astronomy
Identifiers
urn:nbn:se:uu:diva-308359 (URN)978-91-554-9765-1 (ISBN)
Public defence
2017-01-13, Polhemsalen, Ångströmslaboratoriet, Lägerhyddsv. 1, Uppsala, 13:30 (English)
Opponent
Supervisors
Available from: 2016-12-22 Created: 2016-11-24 Last updated: 2016-12-28Bibliographically approved

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