[ExI] On vacation until July 2 Re: Tabby's star

[Stuart LaForge]

Quoting Keith Henson via extropy-chat <extropy-chat at lists.extropy.org>:

> It's been a very long time since the problems of computing out in
> space were discussed here.  We may be seeing a K2.  It looks like they
> are using a huge structure to hold the power and radiating equipment.
> This way you get a fixed speed of light delay on the computing
> elements.
>
>
> The diameter of Tabby's star is ~1099206 km
>
> Crossing time from center to center (the dip) is around a day.
>
> D/24*3600 about 12.7 km/s.  In the solar system, the orbital speed for
> Jupiter is 13 km.
>
> M is 6.6743 × 10+11 * 1,43
> G is 1.98847)×10-30  18.97845280903 10+19 v is 12700 m/s
>
> r = GM/v**2  0.11766664274927149854299708599417  10+13, ~7.8 Au

7.8 AU is too far as is 5.2 AU. According to this paper, the dimming  
has a period of 1574 days or 4.31 years so by Kepler's 3rd law, an  
orbital semimajor axis of 2.98 AU. The center of circumstellar  
habitable zone for a star 4.68 times the sun's luminosity is the  
square root of the the luminosity times the distance to the center of  
the suns habitable zone or sqrt(4.68) * 1.34 AU = 2.90 AU. So whatever  
is orbiting the star is pretty close to dead center of the life zone.

https://arxiv.org/abs/1710.01081

Abstract
Observations of the main sequence F3V star KIC 8462852 (also known as  
Boyajian's star) revealed extreme aperiodic dips in flux up to 20%  
during the four years of the Kepler mission. Smaller dips (< 3%) were  
also observed with ground-based telescopes between May 2017 and May  
2018. We investigated possible correlation between recent dips and the  
major dips in the last 100 days of the Kepler mission. We compared  
Kepler light curve data, 2017 data from two observatories (TFN, OGG)  
which are part of the Las Cumbres Observatory (LCO) network, as well  
as archival data from the Harvard College Observatory (HCO), Sonneberg  
Observatory, and Sternberg Observatory, and determined that  
observations appear consistent with a 1,574-day (4.31-year)  
periodicity of a transit (or group of transits) orbiting Boyajian's  
star within the habitable zone. Comparison with future observations is  
required to validate this hypothesis. Furthermore, it is unknown if  
transits that have produced other major dips as observed during the  
Kepler mission (e.g. D792) share the same orbital period.  
Nevertheless, the proposed periodicity is a step forward in guiding  
future observation efforts.

>
> Jupiter is 5.2 AU
>
> luminosity is 4.68, so at 1 au 6388 W/m^2, this power is divided by
> 7.8^2 tp get 105 W/m^2,  ~0.1 GW/square km.
>
> The area of Tabby's star is D/2 squared x pi .  22% blocked would be
> 208771274655 square km, 409 times the area of the earth.  As a square,
> 456914. km on one side..
>
> The input power is over 1220 times what the human race uses
>
> To radiate 105 W at 65K (measured), the radiator surface will need to
> be about 50 m^2 for every square meter of light input.  This looks
> like it is optimized for computation.
>
> Because the radiators can't view either other, the whole thing might
> be implemented as a deep V-shaped wedge with the sunlight going down
> the middle and the radiators on the outside
>
> Comments welcome.  If you want to check the math, please do.
>
> Keith

I think the reason we are not seeing a ton of IR is that they are  
radiating their waste heat axially instead of radially. In fact, you  
suggested that yourself on the list several years ago for a K2 trying  
to be stealthy.

Stuart LaForge