Читать книгу Planet Formation and Panspermia - Группа авторов - Страница 34

As an extension of galactic habitability, the supergalactic habitable zone was described in [4.25]. They argued that near the center of large clusters and superclusters of galaxies, the intensive interactions of galaxies create inhospitable conditions for life and that life should rather thrive at the outskirts of these structures. Large massive galaxies are often found near the centers of galactic clusters and can have many minor mergers with smaller galaxies during their lifetime. The authors also argue that small galaxies might offer the best habitable conditions. Other papers have argued that dwarf galaxies and satellites of large galaxies might offer the best conditions for life [4.13, 4.28]. Massive clusters of galaxies are also likely to contain galaxies with an extremely active galactic nuclei, notably quasars, that could have a significant habitability impact. A consideration of habitability near the supermassive black holes is considered in [4.32], while habitability near the centers of spiral galaxies is considered in [4.7].

The plethora of galactic interactions within superclusters of galaxies, that account for the visible part of the fabric of our universe, including most obvious ones such as mergers and flybys, can significantly influence the habitability conditions in individual galaxies. In example, the energetic explosions of dying stars or mergers of stellar remnants could eject gas and dust well outside the plane of the galactic disk where it can get picked-up by a satellite galaxy such as the one of the Magellanic Clouds. Apart from incorporating and exchanging gaseous and stellar components of one another, interacting galaxies can also mix their populations of interstellar small bodies and rogue planets. In addition, the galactic mergers are usually not catastrophic events as far as stellar systems are concerned, but rather the individual stars can find themselves orbiting within new galactic hosts without significantly disturbing their planetary systems. If humanity survives long enough, then a likely scenario is that we will find ourselves inside the Andromeda Galaxy in the distant future. Unlike star orbiting planets, the stars can readily change their galactic host after completing only a handful of galactic orbits that last ~108 yr. Given the ~1010 yr age of the universe, the galaxies appear as a relatively more dynamical environment in this respect than individual stars, with far more pronounced matter exchange.

A first discovery in this respect is a meteor, with velocity parameters consistent with an extragalactic origin [4.3]. In addition, more voluminous prospects should stem from the Milky Way and its rich history of interactions with other galaxies. Perhaps, even our Sun originated in other galaxies interacting with ours during the last 10 Gyr. Future habitability studies that will integrate Milky Way stellar orbits using data from GAIA space mission are likely to offer a probability for such a radical conjecture.