Asri-unix.888
net.space
utcsrgv!utzoo!decvax!ucbvax!sri-unix!HPM@CMU-20C@Berkeley@CCA-UNIX
Wed Mar 3 18:30:54 1982
Quasar starships
Re:
1) Short term brightness changes in quasars
Paragraph from "The Evolution of Quasars" by Maarten Schmidt
and Francis Bello May 1971
"Unlike the light output of normal galaxies, the light output
of some quasars has been observed to change significantly
in a matter of days. The only explanation is that some variable
component, if not the entire quasar, may be much larger than
the solar system." - One point for the starship hypothesis.
2) Long term brightness changes
Since short term changes are irregular, there must be some. In
any case, the 20 years since the first quasar discovery is a short
interval in a 1000 year trip. Anybody have data on this?
3) Increases in red shift with time
I chose .001 g as a plausible acceleration because it allows a
continuously accelerated 1000 light year trip in a total conversion
photon rocket with a mass ratio under 10. By comparison, at .01 g
the mass ratio is nearly 200. Over a 10 year period .001 g gives
a velocity change of .01 c, from .82c to .83c at typical quasar
velocity, a change in redshift from 2.18 to 2.28. The quasar
articles I've seen give redshifts to two decimal places, so a
change of this magnitude should be detectable. Any lower bounds
on redshift change known? A less than .01 change in ten years
would imply an acceleration of less than 10e-5 g.
Low values could be explained as being reasonable for something
less than total conversion. (The spectral lines (H, C, Mg) of
quasars show that there is a mix of stuff there). A detected
increase in redshift would be very strong evidence for a rocket,
but lack of such would be a strong negative indication. Any data?
4) Density correlation with the galactic disk
The stellar neighborhood is pretty isotropic in a thousand lightyear
sphere, and farther away they would be harder to see. Also, most quasar
searches have been made out of the galactic plane, because the
in-plane sky is so cluttered. A quasar set against a background
of a galactic dust cloud would, of course, be wonderful evidence
of them being nearby. But only 200 have been found so far, so the
evidence is not yet in. The Feb 82 Osmer Sci. Am. article statement
that there seems to be no correlation between redshift and brightness
is positive evidence.
Perhaps related, from the same article: "The spectra of quasars are
quite unlike the spectra of all other astronomical objects ...
The strongest feature is the Lyman-alpha line of atomic hydrogen ...
... in many instances the lines are wide, an indication that
some of the gas surrounding the quasar is moving at velocities as
high as [ 0.1 c ]. The physical conditions deduced from the various
lines show that the gas is hotter than the gas in normal nebulas ..."
5) Power output of a quasar-bright starship (other message)
Yes, the huge energy output is entirely predicated on them
being at the edge of the visible universe. Their power output
drops by inverse square law. If they are at 10e10 light years,
their output (if isotropic) is that of 10e13 stars.
If they are only 1000 lightyears distant and isotropic the
output is one tenth that of a star.
If the power output is concentrated into a one degree of
divergence beam, one millionth of a stellar output suffices.
This is 10e27 ergs per second.
If the power for this last case is provided by total
conversion, it means conversion of 1000 kg, or 1 tonne, of
fuel per second - Certainly awesome by our standards, but
much smaller than astronomical in scale, and probably not
absurd for a mature starship technology.
Assuming, as before, a 1000 light year trip and 10 mass ratio,
thus .001 g acceleration we can calculate that the mass of a
typical quasarship to be 10^11 tonnes, 100 billion tonnes.
(By comparison, the earth masses 10^22 tonnes.) If the ship
has the density of water, it might be contained in a sphere
10 kilometers in diameter. (Sounds just right to me!)
Because of the small fraction of such ships which would
have their narrow beams aimed at us, the density of visible
quasars would imply that there are maybe 100 billion of these
cuties within a few thousand light years. Could be big
trouble later if they're not very friendly.
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