New version of old Fermi Paradox solution: extraterrestrial intelligence can exist in internal sectors of the Galactic disk and think that the Solar neighborhood is empty
Аннотация: Thoughts came to me after reading of the first paper in October 2020. Decision to write them down was made just in July 2021.
NEW VERSION OF OLD FERMI PARADOX SOLUTION: EXTRATERRESTRIAL INTELLIGENCE CAN EXIST IN INTERNAL SECTORS OF THE GALACTIC DISK AND THINK THAT THE SOLAR NEIGHBORHOOD IS EMPTY
Sozdatelev A. S.,
master in IT (and amateur astronomer)
The significant part of people has ever heard about Fermi Paradox, so we don't concentrate attention at this topic. For ignorant ones there is the short explanation that its approximate formulation - if extraterrestrial civilizations exist, why we don't observe them?
In September, 2020, the article [1] was published that contains diagrams of supernova and gamma-ray events' occurrence distributions within our Galaxy. These astronomical catastrophes can make large harm to biosphere even at enough long distance. Additionally, at graphs lines of terrestrial planet density based on current dataset analysis was plotted.
Due their constructions, about 10 billion (1010) years ago the most safe areas were the outer edge of disk and the galo at the distances of more 15 kiloparsecs from the Galactic center. Then, count of flares began to rise at peripheries and decrease in inner and middle parts of disk.
At outskirts of the Galaxy the rate had the peak in 6-8 events between 5 and 1 billion years ago (4-6 now). The probability of complex live forms' existence was primarily very low in this area, because of low density of stellar population and low metallicity concentration of terrestrial planets also was low (below 10-2 for red dwarfs и 10-3 for solar-type stars (FGK)), water can prevail in their composition as in the composition of initial protoplanetary disks [2, 3]. Civilizations, if they appeared in early period, must adapt or migrate from becoming unsafe region. In first case, they must create special technologies which we can imagine, but not realize. Feasibility of the second variant was very difficult because of large distances to the nearest suitable system; such long travel is more probable for civilization of non-biological creatures.
In internal areas of the Galactic disk, at the distances of 2,5-3 kps quantity slowed down to enough low incidence in 6-8 flares 6-7 billion years ago [1, 2, 3]; even 4 billion years, in the beginning of life at the Earth, there were 2-3 events per 500 million years. But 1 billion years ago, in accordance with figure 6, frequency for distances between 3 and 6 kps (by fig. 5 - 2,5-7,5 kps), decrease below one, became the probability that one of them may happen nearly. So it means, that life at some of numerous planets (density of 10 and more per square parsec for FGK, 100 and more for M-stars) of these areas had hundreds million (even till 1.5 billion) years for evolution and, of course, appearance of intelligent species. Less at 1-2 orders distances between systems (several light days and weeks in contrast with several light years) than in the solar neighborhood has simplified studying of nearby systems by optical systems and space probes. According to mathematical modeling [4] and current observations [5], gas giants at wide orbits (as in our system) occurred around binary stars with separation of 1000 (nearly 1/63 l.y.) and more astronomical units, and there are two expressed peaks at 40-50 and 100 astronomical units in exoplanet-hosting binary star systems' separation distribution [6]. Therefore, more stellar density mustn't seriously affect the planet formation processes. There is no need in acceleration to the large relativistic speeds for fast trip to the nearest systems in internal regions of the disk; there is enough ~0.1 or even 0.01 с, that made the Bussard ramjet quite suitable transport. However, distances and travel times remain quite long, that could make these creatures first or later muse about possibility to get over light speed limitation (even though by Alcubierre drive).
I often face the statement that the Solar system lies at the Galactic edge or the edge of the Galactic disk, but it's wrong. In fact, it's situated close to middle plane at a distance of nearly 8 kiloparsecs or 26 000 light years from the Galactic centre, and the disk's radius equals 50 000 light years (about 16 kiloparsecs), i.e. we reside in the middle part of the disk.
In the Solar neighborhood for last 500 million years count of events equals ~1.3; factually, it means that Sun and its neighbors were too close to one or two flashes. In this work [1] authors represent arguments that Ordovic mass extinction, happened about 445 million years ago, was caused by long gamma-ray burst. Two with half months before, July 17, the article of geologists was published [7], they found in deep ocean ferromanganese crusts dated between 1.5 and 4 million years high amounts of 53Mn and 60Fe, that fact indicates relatively close supernova that probably happened about 2.5 million years ago; this event is supposed to increase cloud formation that became the reason of several glaciations of the Pleistocene [8]. On August, 18, 2020 another article was published [9]; it contains results of the analysis of the end-Devonian fossils dated 359 million years ago. The authors report the discovery of spores with distinct morphologies including malformed spines and dark pigmented walls, features consistent with severely deteriorating environmental conditions, and UV-B damage following destruction of the ozone layer. With detecting either of the long-lived radioisotopes 146Sm or 244Pu in end-Devonian extinction strata it would confirm hypothesis of a supernova origin, point to the one or several core-collapse explosions of a massive star, at a distance of ~20 parsecs, just in two radiuses of "kill distance" that would have precipitated a full mass extinction.
Noteworthy, the same diagram shows that during period of the Solar System's formation there were 15-20 flares per 500 million years in the neighborhood. So primitive life forms survive though cosmic circumstances severity; Ordovic mass extinction is the earliest one, by that time multicellular forms had already existed, but not yet appeared at the land.
Half of nearby stars is older than the Sun (for example, the age of the Alpha Centauri is at least 4,85 billion years, tau Ceti - about 5,6 billion), others are much younger (less 3 billion years). If theoretical constructions are right, there is a high probability that no other civilizations are located within 500 or even 1500 parsecs (nearly 1 630 and 4 900 light years respectively) from us. They must reside in the internal regions of the disk and make about our area corresponding conclusions: apart from frequent radiation cataclysms, terrestrial planets' density at 1-2 orders and solar-type stars' rate in our region below than in secure and populous internal sectors. Therefore, we live in "backwoods", underpopulated district of the Galaxy. Those creatures can consider our sector to be far desert (even with faster-than-light transport means) territory, where nobody or a few ones live and nothing interesting for visit.
Many variants - positive and negative - of the Contact were invented in science fiction, but there are few stories, in which human race was ignored by them; I primarily remembered Strugatsky brothers' novel "Roadside Picnic". At some point, I have imagined the following situation: we will find other civilizations by constructions or functioning trace of their technospheres in thousands light years from us, they could have already discovered our planet and life at it, but haven't done anything about these facts. And no actions have been made to each other. Total indifference to other living and intelligent forms' existence.
Thus, the Earth is an oasis, miraculously remained among scorched by radiation space desert. We really reside at the Galactic edge, but not in direct, just in a figurative sense, far from the main clusters of habitable worlds. But stars in the Solar neighborhood may host not only destroyed or burnt by flares planets, but also lifeless and with appropriate for life conditions ones or planets where only primitive forms of life survived. Two last named categories are appropriate for colonization by humans and all earth life.
References
1. R. Spinelli, G. Ghirlanda, F. Haardt, G. Ghisellini, G. Scuderi "The best place and time to live in the Milky Way" (https://arxiv.org/pdf/2009.13539.pdf)
3. Cabral Nahuel, Nadège Lagarde, Céline Reylé, Aurélie Guilbert-Lepoutre and Annie C. Robin "Chemical connections between low-mass stars and planet buildingblocks investigated by stellar population synthesis" (https://arxiv.org/pdf/1902.07484.pdf)
4. Daohai Li, Alexander J. Mustill, and Melvyn B. Davies "Encounters involving planetary systems in birth environments: the significant role of binaries" (https://arxiv.org/pdf/2008.08842.pdf)
5. Clémence Fontanive and Daniella Bardalez Gagliuffi "The Census of Exoplanets in Visual Binaries: population trends from a volume-limited Gaia DR2 and literature search" (https://arxiv.org/pdf/2101.12667.pdf)
6. Steve B. Howell, Rachel A. Matson, David R. Ciardi, Mark E. Everett, John H. Livingston, Nicholas J. Scott, Elliott P. Horch, and Joshua N. Winn "Speckle Observations of TESS Exoplanet Host Stars: Understanding the Binary Exoplanet Host Star Orbital Period Distribution" (https://arxiv.org/pdf/2101.08671.pdf)
8. Stellar explosion in Earth's proximity - Discovery of iron-60 and manganese-53 substantiates supernova 2.5 million years ago (https://www.tum.de/nc/en/about-tum/news/press-releases/details/36198/)
9. Brian D. Fields, Adrian L. Melott, John Ellis, Adrienne F. Ertel, Brian J. Fry, Bruce S. Lieberman, Zhenghai Liu, Jesse A. Miller, and Brian C. Thomas "Supernova triggers for end-Devonian extinctions" (https://www.pnas.org/content/117/35/21008)