Hello Space Fans and welcome to another edition
of Space Fan News.
In this episode, on this day of the momentous
second data release of the Gaia spacecraft,
astronomers from the University of Uppsala
in Sweden have been working on a way to find
Dyson Spheres and other megastructures that
may be around other stars in our galaxy that
would provide our first confirmation of other
civilizations in the Milky Way Galaxy.
In a paper published on the preprint site
Astro-ph this week, a group of SETI astronomers
from the University of Uppsala in Sweden describe
a technique for locating the signatures of
star-covering artificial structures known
as Dyson Spheres and any other suitably large
megastructures that may be in orbit around
a star.
This comes in advance of the second data release
of the Gaia mission which today released the
most accurate positions ever made of 1.7 billion
stars in our galaxy.
For those who don’t know, a Dyson Sphere
is a hypothetical sphere that covers all or
part of a star.
By constructing a Dyson sphere out of material
from dismantled planets, extremely advanced
civilizations could in principle tap into
a significant fraction of the radiation power
of their host star.
Dyson spheres are typically not imagined as
a solid shell, but rather as a dense, spherical
swarm or shroud of absorbing satellites, with
each satellite absorbing a small fraction
of the stellar radiation.
Other, less ambitious astro-engineering designs,
where sparse swarms, rings or single large
shades are built around both stars and stellar
remnants have also been considered in the
paper, and the time to build a small scale
megastructure of this type has been estimated
at as little as a hundred years.
Who knows how long it would take to build
a full-on Dyson Sphere.
The paper outlines what a Dyson Sphere might
look like in Gaia data.
I’ve told you about Gaia a couple of times
before on SFN but it is an ESA mission designed
to accurately measure the positions of about
a billion stars in our galaxy out to 30,000
light years with an accuracy never before
achieved.
Launched in December 2013, Gaia's mission
is scheduled to last for five years.
During that time, it will log the position,
brightness and color of every visible celestial
object that falls within its field of view.
By repeating these observations throughout
its mission, astronomers will be able to calculate
the distance, speed and direction of motion
of each of these objects, chart variations
in their brightness, and determine whether
they have nearby companions.
From Gaia data, astronomers are able to get
distances by measuring parallax, where you
measure the shift in position of a star relative
to the background stars, a standard trigonometric
technique that astronomers have been using
for hundreds of years but is only accurate
for close stars between 500-1000 parsecs from
Earth and Gaia is doing better than it’s
ever been done.
But there is another parallax method, called
spectrophotometric parallax, which is a technique
that works for stars much further out, out
to about 10,000 parsecs from Earth, but it
really only works with stars on the Main Sequence
(which is fine, because we’re looking for
civilizations here and Main Sequence stars
are a good place to look).
Spectrophotometric parallax measurements are
done from ground-based observatories and there
are many projects which compare the two methods
as a sort of check on each other.
OK so back to Dyson Spheres.
Since a star surrounded by a partial Dyson
sphere with a large fraction of the star being
covered will appear unusually faint for its
spectral type at optical and near infrared
wavelengths, its spectrophotometric distance
will be overestimated.
Why?
Because its faintness gives a false reading
for it’s distance since it’s artificially
covered.
Spectra rely on flux or light output.
A trigonometric parallax measurement, as provided
by Gaia would, on the other hand, still be
able to provide an accurate distance estimate
- it is dependent only on its position relative
to background stars.
So, it should be possible single out tentative
Dyson-sphere candidates by comparing parallax
distances to their spectrophotometric counterparts.
According to the paper, a large Dyson Sphere
covering a large percentage of a star’s
radiation power will appear to be closer to
Earth in the Gaia data when computing the
distance using the regular parallax method.
However, because a star of a given spectral
type would be much dimmer than expected (since
it’s covered by a bunch of advanced civilization)
the spectrophotometric parallax would be off,
it would appear further away.
So that means the trigonometric parallax provided
by Gaia would reveal the true distance of
the Dyson Sphere and comparing the two results
computed from the Gaia dataset, any discrepancy
should be a candidate star for more study.
A shorter parallax distance of a star as compared
to its spectroscopic parallax might indicate
a Dyson Sphere or other megastructure in orbit
around that star, and would definitely warrant
a closer look.
The authors of the paper also say that this
technique will only work if the fraction of
the star covered by the Dyson Sphere is significant,
like more than 75% of the star’s radiation
is blocked from us.
Well that is it for this episode Space Fans,
thanks to all of our Deep Astronomy Patreon
Patrons who keep these episodes coming.
Thanks to all of you for watching and as always,
Keep Looking up!
