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Thread: Astrobiological papers from Arvix and everywhere

  1. #61
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    Living near the galactic core is very very VERY bad for you. It is a reasonable assumption, based on this paper, that no one lives there anymore, if anyone ever did.


    https://arxiv.org/abs/1902.07950

    Comparative analysis of the influence of Sgr A* and nearby active galactic nuclei on the mass loss of known exoplanets

    Agata M. Wisłocka, Andjelka B. Kovačević, Amedeo Balbi (Submitted on 21 Feb 2019)

    The detailed evolution of exoplanetary atmospheres has been the subject of decade-long studies. Only recently, investigations began on the possible atmospheric mass loss caused by the activity of galactic central engines. This question has so far been explored without using available exoplanet data. The goal of this paper is to improve our knowledge of the erosion of exoplanetary atmospheres through radiation from supermassive black holes (SMBHs) undergoing an active galactic nucleus (AGN) phase. To this end, we extended the well-known energy-limited mass-loss model to include the case of radiation from AGNs. We set the fraction of incident power ϵ available to heat the atmosphere as either constant (ϵ=0.1 ) or flux dependent (ϵ=ϵ(F XUV ) ). We calculated the possible atmospheric mass loss for 54 known exoplanets (of which 16 are hot Jupiters residing in the Galactic bulge and 38 are Earth-like planets (EPs)) due to radiation from the Milky Way's (MW) central SMBH, Sagittarius A* (Sgr A*), and from a set of 107,220 AGNs generated using the 33,350 AGNs at z<0.5 of the Sloan Digital Sky Survey database. We found that planets in the Galactic bulge might have lost up to several Earth atmospheres in mass during the AGN phase of Sgr A*, while the EPs are at a safe distance from Sgr A* (>7 kpc) and have not undergone any atmospheric erosion in their lifetimes. We also found that the MW EPs might experience a mass loss up to ∼15 times the Mars atmosphere over a period of 50 Myr as the result of exposure to the cumulative extreme-UV flux F XUV from the AGNs up to z=0.5 . In both cases we found that an incorrect choice of ϵ can lead to significant mass loss overestimates.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

  2. #62
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    Binary stars might not be such bad places for habitable planets after all. Well, 1-2 times in 352, that is.

    https://arxiv.org/abs/1903.01995

    Enlarging habitable zones around binary stars in hostile environments

    Bethany A. Wootton, Richard J. Parker (Submitted on 5 Mar 2019)

    Habitable zones are regions around stars where large bodies of liquid water can be sustained on a planet or satellite. As many stars form in binary systems with non-zero eccentricity, the habitable zones around the component stars of the binary can overlap and be enlarged when the two stars are at periastron (and less often when the stars are at apastron). We perform N-body simulations of the evolution of dense star-forming regions and show that binary systems where the component stars originally have distinct habitable zones can undergo interactions that push the stars closer together, causing the habitable zones to merge and become enlarged. Occasionally, overlapping habitable zones can occur if the component stars move further apart, but the binary becomes more eccentric. Enlargement of habitable zones happens to 1-2 binaries from an average initial total of 352 in each simulated star-forming region, and demonstrates that dense star-forming regions are not always hostile environments for planet formation and evolution.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

  3. #63
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    Maybe aliens use black holes to power their starships. Seriously.

    https://phys.org/news/2019-03-gamma-...s-powered.html

    Gamma ray telescopes could detect starships powered by black hole
    March 7, 2019, Universe Today

    In the course of looking for possible signs of extra-terrestrial intelligence (ETI), scientists have had to do some really outside-of-the-box thinking. Since it is a foregone conclusion that many ETIs would be older and more technologically advanced than humanity, those engaged in the Search for Extra-Terrestrial Intelligence (SETI) have to consider what a more advanced species would be doing. A particularly radical idea is that spacefaring civilizations could harness radiation emitted from black holes (Hawking radiation) to generate power. Building on this, Louis Crane, a mathematician from Kansas State University (KSU), recently authored a study that suggests how surveys using gamma telescopes could find evidence of spacecraft powered by tiny artificial black holes. The study, "Searching for Extraterrestrial Civilizations Using gamma Ray Telescopes," recently appeared online. This is the second paper published by Dr. Crane on the subject, the first of which was co-authored by Shawn Moreland (a physics grad student with KSU) and published in 2009 – titled "Are Black Hole Spacecraft Possible?"
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

  4. #64
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    Are A-stars good prospects for habitable planets? This papers suggests they might be.

    https://arxiv.org/abs/1903.03706

    Habitable zone predictions and how to test them

    Dorian S. Abbot, et al. (Submitted on 9 Mar 2019)

    The habitable zone (HZ) is the region around a star(s) where standing bodies of water could exist on the surface of a rocky planet. The classical HZ definition makes a number of assumptions common to the Earth, including assuming that the most important greenhouse gases for habitable planets are CO2 and H2O, habitable planets orbit main-sequence stars, and that the carbonate-silicate cycle is a universal process on potentially habitable planets. Here, we discuss these and other predictions for the habitable zone and the observations that are needed to test them. We also, for the first time, argue why A-stars may be interesting HZ prospects. Instead of relying on unverified extrapolations from our Earth, we argue that future habitability studies require first principles approaches where temporal, spatial, physical, chemical, and biological systems are dynamically coupled. We also suggest that next-generation missions are only the beginning of a much more data-filled era in the not-too-distant future, when possibly hundreds to thousands of HZ planets will yield the statistical data we need to go beyond just finding habitable zone planets to actually determining which ones are most likely to exhibit life.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

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