February 09, 2016

Physics PHD reader of Nextbigfuture proposes megamirror system to explain Star seen dimming for 100 years

Charles Engelke (physics PhD from MIT 1986) and a researcher in Boston College’s Institute for Scientific Research submitted a theory that the unusual dimming of the star KIC8462852 is a megamirror system.

Since he saw the Nextbigufuture posting on Bradley Schaefer’s reconstruction of the star’s 1890-1990 light curve, he has been mulling over an hypothesis on the potential nature ofc megastructures satisfying all the observations. (quick fact: at MIT Bradley’s favored expletive was “Dagnabit!” and he started the famous MIT mystery hunt tradition, a very memorable character). The hypothetical explanation I have in mind seems to hang together pretty well after several days of contemplation. It involves huge light weight mirrors and interstellar travel.


Nextbigfuture had the article - Star dimming for 100 years with irregular dips in brightness consistent with Dyson swarm construction and orbiting of partial Dyson Swarm

I [Charles] have always greatly enjoyed the imaginative ideas and future possibilities you collect on NextBigFuture and thought it might be an appropriate forum for consideration of the ideas I have been examining.

I wondered if you might want to post a piece about it on your website.**



Why Mega Mirrors?

All would agree that the absence of any infrared excess comparable to the visible flux intercepted by the occulting objects would be no mystery if the interceding objects were perfect mirrors and the stellar flux was merely being redirected out into space. But why would aliens go to such lengths just to do that? I suggest that it is the natural prerequisite for practicing large scale interstellar travel in the manner God and nature apparently intended.

Just imagine that, despite their size, these mirrors can be shaped to optical quality. What is the diffraction limit on what a telescope with a primary mirror more than half the diameter of our sun (I estimate D~ 8e8m to cause of 22% dip) can resolve in visible light (~5e-7m)? Somewhere on the order of 1e-16 radians. Since a parsec is 3e16 meters that means they could resolve objects on the order of 10’s of kilometers on Earth when viewed from 454 pc. So, great for astronomy.

Now assume that a similar size mirror is placed close to the star’s surface and shaped to redirect the spreading rays it intercepts into parallel rays bounced past the limb of the star. The beam would have an intensity comparable to the surface of a 6750 K blackbody, a diameter about equal to that of our Moon’s orbit, and would spread out due to diffraction by only 50 km more after traveling 1500 light years, so still a beam with the intensity of a star’s surface. Yes, that makes us pretty vulnerable if they should choose to aim the beam mirror rather than the telescope version at Earth, but that discussion is for another article (“How I Learned to Stop Worrying and Love the Mega Mirror” in which I describe my initial ‘discomfort’ before discovering that a form of deterrence should hold, given the 3000 year delay in their knowledge of technological state, and the reasonableness of any planet copying their technology to equip the guidance AI with instructions to fire back at the attacking system continually for the rest of of its’ functional life if an external beam should wipe out the home planet. I do not think mirrors responsible for the ‘Fermi paradox’).

How massive would a similar size ‘solar sail’ mirror be? Well, unlike Dyson spheres, mirrors, and especially sails can be quite thin, so figuring on some tens of grams per square meter one gets ~2e16 kg, something like the mass of an asteroid with diameter of order 20 km would suffice as building material.

The light pressure in the ‘beam’ from the initial mirror would supply twice that pressure to this lightsail upon being reflected, sufficient to provide the sail a constant acceleration of several times g=10m/s^2. By hanging a starship of similar mass on the sail, the acceleration can be made equal to that of the passenger’s home planet, and all the inhabitants of the planet could indeed probably be accommodated in a ship of such mass simultaneously. At 1 g constant acceleration they could journey ‘anywhere’ experiencing only a couple of decades of onboard time due to time dilation (or less than one decade at 2 g’s). However, unless the home star is about to go up in flames and an ark is needed for evacuation, this ‘beam-filling’ sail is overkill.

We can assume the big beam is big just so it won’t spread and thinout due to diffraction. Smaller starships and with sails proportioned in scale with their small mass can travel within the bigger beam with the same level of acceleration. Energy not hitting the sail is not ‘wasted’ since stars always pour out energy, the megastructure aliens have just redirected it, their only expense is in building the original structures and maintaining focus and aim. The ships themselves are simple affairs. No need for huge stores of fuel, for Bussard ramjet complications, for antimatter, for generation ships. You just jump in a beam and the rest is free. (But you must trust the operators to remember you if you go off on a 1000 lyr expedition or something). It would have been the obvious way to go from the first, at least in principle, if we could just think ‘big enough’.

Stopping at the destination can be done using a smaller ‘drouge shoot’ mirror-sail deployed out the back of the starship. Meanwhile, he original sail in front would be released, but the reflected annular beam from it would strike the deceleration sail and the starship slows. This would require an optically controlled original sail.

The primary ‘deflect and direct’ mirrors need to be positioned‘near’ the star’s surface and kept stationary relative to the sky (except those scanning it for astronomical purposes). Therefore they must be ‘floated’ on the star’s own light pressure in order to counter the star’s gravity without orbital motion. At a distance of 3 to 4 stellar radii (I am assuming the star is 1.25* solar radius and 1.5* solar mass) the gravitational acceleration would be in the range of a few g’s and they could be ballasted to float with structural forces similar to those involved in the active starship and sail situation.

The mirrors are probably stabilized on an open work spherical network of rings around the star, having enough mirrors to support and expand the whole structure equally under some degree of tension. Schaefer may have been documenting the addition of more mirrors to support and balance the whole as it was initially built up, or the accumulation of mirrors on the side of the star near us as commerce was increasing with other star systems in that general direction (or perhaps the addition of inactive mirrors just to combat global warming as their star ages).

The neighboring star systems being served would presumably be colonies and perhaps we should look for evidence of more eclipsing stars nearby (but if these colonies are sending beams back toward the home star their mirrors may be facing away from us).

The light curves portraying the dips(reported by Boyajian et al Oct 2015) look more complicated than simple disk shaped mirrors, but the disk model is just for proof of principle and convenience. However, continuing to use the simple disk dimension calculated above, the several day length (maybe 2 or 3?) of the total eclipse down to 15% in Fig 1c and down 22% in Fig 1e indicates a low speed that is either non orbital (or further out than what corresponds to Pluto). The triple dip structure in Fig1e looks roughly periodic with ~25 day recurrence. It could conceivably be the same assemblage of structures coming around three times at slightly differing latitudes (maybe for astronomical scanning purposes, or as a counter rotator to a more massive sphere. That is of course the wildest of guessing, but inspired from the fact that using the assumption the speed deduced from the duration of totality corresponds pretty well to one and a half rotations at 3 or so stellar radii.

A friend of Charles thinks that something like this outer exoplanet giant ring system can explain the data Arxiv - Modeling giant extrasolar ring systems in eclipse and the case of J1407B: Sculpting by exomoons ? M.A. Kenworthy, Leiden Observatory, Leiden University, and E.E. Mamajek

ABSTRACT on Extrasolar ring system
The light curve of 1SWASP J140747.93-394542.6, a 16 Myr old star in the Sco-Cen OB association, underwent a complex series of deep eclipses that lasted 56 days, centered on April 2007. This light curve is interpreted as the transit of a giant ring system that is filling up a fraction of the Hill sphere of an unseen secondary companion, J1407b. We fit the light curve with a model of an azimuthally symmetric ring system, including spatial scales down to the temporal limit set by the star's diameter and relative velocity. The best ring model has 37 rings and extends out to a radius of 0.6 AU (90
million km), and the rings have an estimated total mass on the order of 100 M Moon. The ring system has one clearly defined gap at 0.4 AU (61 million km), which we hypothesize is being cleared out by a exosatellite orbiting around J1407b. This eclipse and model implies that we are seeing a circumplanetary disk undergoing a dynamic transition to an exosatellite-sculpted ring structure and is one of the first seen outside our Solar system.

KIC 8462852 Why Mega Mirrors? Constant acceleration of ‘g’ or greater for relativistic Interstellar travel.

Certainly the absence of any infrared excess comparable to the visible flux intercepted would be no mystery if the interceding objects were perfect mirrors and the stellar flux was merely being redirected out into space. But why go to such lengths just to do that? I suggest that it is the natural prerequisite for practicing large scale interstellar travel in the manner God and nature apparently intended.

Just imagine that, despite their size, these mirrors can be shaped to optical quality. What is the diffraction limit on what a telescope with a primary mirror more than half the diameter of our sun can resolve in visible light? Somewhere on the order of 1e-16 radians (I estimate D~ 8e8m to cause the 22% dip and use 5e-7m for wavelength of light ).





Since a parsec is 3e16 meters that means they could resolve objects on the order of 10’s of kilometers on Earth when viewed from 454 pc (pc=parsec=3.26 lightyears). So, mega mirrors would be great for astronomy.

Now assume that a similar size mirror is placed close to the star’s surface and shaped to redirect the spreading rays it intercepts into parallel rays bounced past the limb of the star. The beam would have an intensity comparable to the surface of a 6750 K blackbody, a diameter about equal to that of our Moon’s orbit, and would spread out due to diffraction by only and additional 50 km after traveling 1500 light years, so still a beam with the intensity of a star’s surface.

How massive would a similar size ‘solar sail’ mirror be? Well, unlike Dyson spheres, mirrors, and especially sails can be quite thin, so figuring on some tens of grams per square meter one gets ~2e16 kg, something like the mass of an asteroid with diameter of order 20 km would suffice as building material.

The light pressure in the ‘beam’ from the initial mirror would supply twice that pressure to this lightsail upon being reflected, sufficient to provide the sail a constant acceleration of several times g=10m/s^2. By hanging a starship of similar mass on the sail, the acceleration can be made equal to that of the passengers home planet, and all the inhabitants of the planet could indeed probably be accommodated in a ship of such mass simultaneously. At 1 g constant acceleration they could journey ‘anywhere’ experiencing only a couple of decades of onboard time due to time dilation (or less than one decade at 2 g’s). However, unless the home star is about to go up in flames and an ark is needed for evacuation, this ‘beam-filling’ sail is overkill.

We can assume the big beam is big just so it won’t spread out and weaken due to diffraction (even for intergalactic distances). Much smaller starships with sails proportioned in scale with their small mass can travel within the bigger beam with the same level of acceleration. Energy not intercepted by the sail is not ‘wasted’ since stars always pour out energy, the megastructure aliens have just redirected it, their only expense is in building the original structures and maintaining focus and aim. The ships themselves are simple affairs. No need for huge stores of fuel, for Bussard ramjet complications, for antimatter, for generation ships. You just jump in a beam and the rest is free. (But you must trust the operators to remember you if you go off on a 1000 lyr expedition or something). It would have been the obvious way to go from the first, at least in principle, if we could just think ‘big enough’.

Stopping at the destination can be done using a smaller ‘drouge shoot’ mirror-sail deployed out the back of the starship. Meanwhile, he original sail in front would be released, but the reflected annular beam from it would strike the deceleration sail and the starship slows. This would require an optically controlled original sail.

The primary ‘deflect and direct’ mirrors need to be positioned‘near’ the star’s surface and kept stationary relative to the sky (except those scanning it for astronomical purposes). Therefore they must be ‘floated’ on the star’s own light pressure in order to counter the star’s gravity without orbital motion. At a distance of 3 to 4 stellar radii (I am assuming the star is 1.25* solar radius and 1.5* solar mass) the gravitational acceleration would be in the range of a few g’s and they could be ballasted to float with structural forces similar to those involved in the active starship and sail situation


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