dietz@SLB-DOLL.CSNET (Paul Dietz) (12/04/85)
Recently, astronomers have discovered bizarre large scale structure
in radio emissions around the galactic nucleus. Using the Very Large
Array (VLA) in New Mexico, astronomers have found large arcs of radio
emission, apparently indicating interstellar magnetic fields of
around 1E-4 gauss. They guess these fields are generated by
dynamo-action in hot gas near the galactic center, perhaps around
a black hole.
Most unexpected, however, was the discovery of dim, smooth, gently
curved lines of emission called "threads". These threads extend
from the galactic nucleus about 30 parsecs and are less than 0.5 parsecs
wide. Astronomers have apparently not yet explained their existence.
They appear to be too regular to be shock fronts, there is no evidence
for a source if they are jets of matter, and, because they curve
away from the core, they are probably not the tracks of natural objects
(stars thrown out of a tight cluster, for example). (See Science, Vol.
230, pages 652-653, Nov. 8, 1985).
Freeman Dyson ("Interstellar Propulsion Systems", in "Extraterrestrials:
Where Are They?", M. Hart and B. Zuckerman, Eds., Pergamon Press, 1982)
has suggested that interstellar spacecraft might slow down by
transferring energy to the interstellar plasma by Alfven drag. As Dyson
says:
"If it turns out that interstellar braking systems are feasible,
then we have a new way to look for evidence of extraterrestrial
intelligence. Look for skid marks on the road! A vehicle braking
from high velocity will leave behind it a long straight tail
of hot plasma which should be a source of persistent broad-band
radio emission. Radio astronomers interested in CETI should be on the
look-out for straight tracks of glowing plasma in the sky."
Engaging in unbridled speculation, I'll hypothesize the threads are
skid marks of ET spacecraft. The galactic core is a good place to brake
because the gas is dense and because the interstellar magnetic
field is strong (Alfven drag being proportional to the square
of the local magnetic field). The vehicles may be intergalactic
spacecraft, slowing down after entering this galaxy at near light speed
(after having been accelerated using a laser-propelled light sail,
say). Alternately, perhaps the galactic core has a lot of interstellar
traffic and we're seeing some of it (maybe Bussard ramjets or
ram-augmented interstellar rockets are more feasible in the core,
and we're seeing their wakes.)