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Comment by erdevs | Hacker News Reader

Good ol' PV on Kinja (from the linked gizmodo article: http://gizmodo.com/the-so-called-alien-megastructure-just-go...) has some interesting thoughts, as usual.

> The biggest axe against it being an alien megastructure project is the fact its an F-type star. F-types only live a couple billion years, depending on mass.

> But the drop in the radiant flux... a sustained drop. That could be something far more interesting. If you could do stellar engineering... you could draw the material off an F-type star while altering its core. You could reduce the mass to a G or K star, greatly increasing its lifespan... and gaining trillions upon trillions of tons of raw material with which to build an alien megastructure...

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I'm sorry, I must've missed something important because I've seen pointers to this post elsewhere. Who exactly is "PV on Kinja?"

I think it's a reference to the first comment on the article linked.

"PV" is a user's name on Kinja, which is the commenting system that gizmodo et al use.

Spectral type isn't 1-1 correlate with the star estimated life. Depends on the star mass. Our Sun was one time a F type star.

Question for you Timex Eclair, can I use a star as the engine for my megaship? Pointing all the photons in direction?

Like this?

Of course if this was happening we'd see some unusual proper motion from KIC 8462852. Which we're not. (Did someone check?)

They're coming right for us!!! O_O

You can you use a giant mirror, that directs light to your ship's sail.

I really wonder what would happen if you really had a giant mirror reflecting all the Sun's energy back to itself

Isn't that basically what happens inside the Sun's core anyways?

It would increase the sun's temperature causing it to expand. I guess eventually it would expand out to reach your dyson mirror.

Of course there would be all sorts of secondary effects, lowering the density in the core could slow down the rate of fusion, increased temp would increase it, but no garuntee that the effects would cancel. Also depending on how far out your mirror is the core might not ever notice the change. The outer layers could heat up and destroy your mirror before the increased temperature reaches the core.

You now have to move the whole sun, so I don't see how the problem got any easier by escalating it to huge proportions? Unless you want to leave the sun behind, but then you will lose your propulsion after getting going.

Do we have a "longevity" estimate for Tabby's star?

By estimating how much starlifting would explain the observed luminosity drop, and then backing out the expected increase in the star's life against its flux decrease one could estimate how efficient the "aliens'" energy-harvesting technology is (coupled to a financial discount rate).

Plug its estimated mass (1.43 solar masses [1]) into the expression for main sequence lifetime [2] and you get ~4.1 billion years. But we don't know how old it is (the prevailing assumption seems to be it's old enough to have settled into staid middle-age behavior, making its variability harder to explain [3]).

[1] https://en.wikipedia.org/wiki/KIC_8462852

[2] http://astronomy.swin.edu.au/cosmos/M/Main+Sequence+Lifetime

[3] http://www.americaspace.com/?p=87801

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