UPDATE u2024 April 2018According to recent references*, our galaxy is surrounded on almost all sides by a u201cmoatu201d of Voids. Our Local Group is physically & gravitationally connected to the Virgo Cluster via a Filament some 65 Mlyr long. In turn, Virgo is a u201cnodeu201d in another Filament, perpendicular to ours, which passes from the Ursa Major Cluster, through Virgo, and on to the u201cGreat Attractoru201d of the Centaurus Cluster. Otherwise, however, Voids surround our Filament on almost every flank. Perhaps this u201cmoatu201d of Voids has helped isolate our galaxy from Alien contact?The following figure is a complex composite of others from the recent references*. It shows that the Grus Chain is a Filament which is separated from our Local Group by a Void around 70 Mlyr wide. And judging by its velocity, the Grus Chain is not associated with our own Filament. One end of the Grus Chain (the u201chigh endu201d) is seemingly flowing towards the Great Attractor through one of the Southern Super-Cluster (SSC) u201ctridentu201d of Filaments (SSC-c). The other end of the Grus Chain (the u201clow endu201d) is flowing towards the Great Attractor through the outskirts of the Fornax Cluster and on in through the Antlia-Hydra Filament.* Gerbal & Mazure, Clustering in the Universe (1983); Courtois et al, Cosmography of the Local Universe (2024)Likewise, the Fornax Cluster is split, with the u201chighu201d half (Fornax) flowing into the SSC-b Filament, and the u201clowu201d half (Eridanus) moving along the Antlia-Hydra Filament. Yet, none of these major structures shows any u201cgravitational velocity awarenessu201d or physical connection to our own Filament*. I inexpertly conclude, that the apparent Void between here and Grus is an actual feature of the local Cosmic Web**.* Fornax connects u201cupu201d to Dorado, which connects further u201cupu201d to NGC 1023 and the Local Spur residing u201cunderu201d our own Filament, and which parallels the same u201cupu201d towards Virgo, as shown here.** The 3D data is difficult to comprehend.Super-Galactic X-Y [SGX-SGY] projection u2024 Numbers show u201cverticalu201d (Super-Galactic Z [SGZ]) redshift positions, in thousands of km/s (almost 15 Mpc = 50 Mlyr). SSC Filaments in blue. Antlia-Hydra Filament in purple. The former generally go u201cup & over & downu201d into the Centaurus Great Attractor, whereas the latter goes u201cway down under everything & slightly back upu201d towards the same. None show any obvious influences from our Filament (Local Group to Virgo Cluster). Virgo appears to be a local density maximum, of which weu2019re a peripheral part, with a u201cmoatu201d of Voids almost entirely surrounding & gravitationally isolating us. This u201cmoatu201d of Voids may have u201cprotectedu201d our galaxy from Alien contact to date (???).Advanced Aliens would be ultra energy efficient. They would have ultra advanced means of capturing star light. They would not u201clet photons slip through Their fingersu201d to escape across the Cosmos and betray Their location in space. Plausibly, Their region of space would be dark.I offer that the actual factual presence of an advanced Alien civilization, millions to billions of years old, would be a large u201cdark anomalyu201d in the otherwise visually bright Cosmic Galactic Web of Filaments intersecting at Clusters. I.e. a u201cdark gapu201d within the Large Scale Structure of the Cosmic Web where one would have otherwise expected to observe numerous natural bright galaxies.Inexpertly, there appears to be precisely such a u201cdark gapu201d in our own Local Filament, which leads from our Local Group towards the Virgo Cluster (in one direction) and towards NGC 7582 (in the opposite direction). From publicly available galaxy maps, there seems to be a lack of bright galaxies all the way from here to NGC 7582, some 70 Mly away.Perhaps not impossibly, an advanced Alien civilization actually arose long long ago, around 35 Mly away (u201chalf the distanceu201d)? For ages, They have been exploring & inhabiting the Local Filament, having colonized hundreds of galaxies therein, as far as the NGC 7582 group (in the constellation Grus, on the far side) and NGC 6744 and our Local Group (on the near side)??If this speculation were true, then u201cTheyu201d would presumably be currently en route to the NGC 7582 group (on the far side) and the NGC 6744 group & our own Local Group (on this near side). u201cTheiru201d space-trekking craft would be difficult to detect decelerating (u201cthrusters facing away from usu201d) into the NGC 7582 galaxies at 70 Mly distance. But determined surveys of NGC 6744 and the general direction of here towards the constellation Grus might eventually detect u201cspace contrailsu201d or u201cthruster glareu201d or the like.EDIT: Our u201cLocal Filamentu201d is actually a two-dimensional, vaguely rectangular, u201cLocal Wallu201d or u201cLocal Sheetu201d. The central portion of the u201cGrus Chain (GC)u201d of galaxies, including NGC 7582 in the u201cGrus Quartet (GQ)u201d at 70 Mly distance, conspicuously lies precisely in the plane of our u201cpancakedu201d, flattish u201cLocal Super-Cluster (LSC)u201d aka u201cLocal Sheet (LS)u201d stretching from our galaxy and Local Group out to the Virgo (V) galaxy cluster. Prima facie, the only reason why the GC would align with our LS is if the two are merely the opposite ends of single structure. This is apparent in a plot of Cosmically local structure in u201cSuper-Galactic X vs. Zu201d projected along u201cSG Yu201d:Close inspection of the above shows that Grus Chain (GC) u201ccloudsu201d N2, N4 & H3 align precisely with the wall-like Local Super Cluster (LSC) u201cpancakedu201d in the SG X vs. Y plane (u201cthinu201d in the SG Z direction) . To wit, the middle of the GC appears to be the u201cfar endu201d of our sheet-like Local Wall, separated from our half of the same (our sheet-like LSC) by an anomalous dark gap devoid of the expected dense distribution of bright galaxies.The following figure depicts a view from the u201ctopu201d (Super-Galactic X vs. Y), from above our galactic plane (galactic north pole) which is essentially the same as the plane of our sheet-like LSC u2024 looking u201cdownu201d from a position with high positive Super-Galactic Z (SGZ) coordinate (looking down from the top of the first figure above). Note too that the Eridanus / Fornax / Dorado u201cFornax Super Cluster (FSC)u201d is far below the plane of our sheet-like Local Wall (dashed gray line):Clearly, the dearth of bright galaxies is so extreme that astronomers identify the u201cmissingu201d span (darkly shaded region between the GC & MWG in the above) of our sheet-like Local Wall to be (part of) a Local Void. The anomalous dark gap is also visible u201cfrom the sideu201d (Super-Galactic Y vs. Z viewed from a position far to the positive SG X direction):The Large Scale Structure of the Cosmic Web is basically massive gravitating centers (galaxy clusters) which mutually draw all matter around them into linear structures (filaments) bridging between them. Indeed, the nearest cluster u201cnodesu201d u2024 Virgo (V), Fornax (F), Grus Quartet (GQ) u2024 all are connected by bridging filamentous structures u2024 Leo Spur (LS), cloud N4, Local Wallu2024 except that the latter is u201cmissingu201d a ~15Mpc span in the middle, what may be an anomalous dark gap from here to the u201cremainingu201d Grus Quarter & Grus Chain galaxies u201cat the far endu201d.If the ~50Mly wide dark gap really actually is an advanced Alien civilization, then it is plausibly of order 100u2013200Myr old (if travelling inter-galactically at ~30% of the speed-of-light) or more (if travelling slower).EDIT: If you draw the space-time diagram for u201cThemu201d, you find that u201cTheiru201d location of origin depends upon your assumed choice for u201cTheiru201d expansion speed v1 (geometric units). If u201cTheyu201d are expanding quickly, at near the speed of light, v~1, then you find that u201cTheyu201d originated very near to the NGC 7582 group, which u201cTheyu201d actually overran long long ago, but which we have yet to observe from here & now. It would also mean that u201cTheyu201d have not long occupied the galaxies between there & here, perhaps explaining why there appear to be a few such galaxies still visible in the otherwise u201canomalously darku201d stretch of our Local Filament:
