The chances that we might pick up a transit showing clear signs of extraterrestrial engineering seem

Although I didn't write about the so-called 'Shkadov thruster' yesterday, it has been on my mind as one mega-engineering project that an advanced civilization might attempt. The most recent post was all about moving entire stars to travel the galaxy, with reference to Gregory Benford and Larry Niven's Bowl of Heaven (Tor, 2012), where humans encounter an object that extends and modifies Shkadov's ideas in mind-boggling ways. I also turned to a recent Keith Cooper article on Fritz Zwicky, who speculated on how inducing asymmetrical flares on the Sun could put the whole Solar System into new motion, putting our star under our directional control.
find the cheapest airline tickets The physicist Leonid Shkadov described a Shkadov thruster in a 1987 paper called "Possibility of Controlling Solar System Motion in the Galaxy" (reference at the end). Imagine an enormous mirror constructed in space so as to reflect a fraction of the star's radiation pressure. You wind up with an asymmetrical force that exerts a thrust upon the star, one that Shkadov believed could move the star (with accompanying planets) in the event of a dangerous event, like a close approach from another star. Shkadov thrusters fall into the category of 'stellar engines,' devices that extract significant resources from the star in order to generate their effect.
There are various forms of stellar engines that I'll be writing about in future posts. But to learn more about the ideas of Leonid Shkadov, I turned to a recent paper by the always interesting Duncan Forgan (University of Edinburgh). Forgan points out that Shkadov thrusters are not in the same class as Dyson spheres, for the latter are spherical shells built so that radiation pressure from the star and the gravitational force on the sphere remain balanced, the purpose being to collect solar energy, with the additional benefit of providing vast amounts of living space.
Where Shkadov thrusters find the cheapest airline tickets do remind us of Dyson spheres, find the cheapest airline tickets as Forgan notes, is in their need for huge amounts of construction material. The scale becomes apparent in his description, which is clarified in the diagram below:
A spherical arc mirror (of semi-angle ψ) is placed such that the radiation pressure force generated by the stellar radiation field on its surface is matched by the gravitational force of the star on the mirror. Radiation impinging on the mirror is reflected back towards the star, preventing it from escaping. This force imbalance produces a thrust…
find the cheapest airline tickets Figure 1 : Diagram of a Class A Stellar Engine, or Shkadov thruster. The star is viewed from the pole the thruster is a spherical arc mirror (solid line), spanning a sector of total angular extent 2ψ. This produces an imbalance in the radiation pressure force produced by the star, resulting in a net thrust in the direction of the arrow.
In reality, the reflected radiation will alter the thermal equilibrium of the star, raising its temperature and producing the above dependence on semi-angle. Increasing ψ increases the thrust, as expected, with the maximum thrust being generated at ψ = π radians. find the cheapest airline tickets However, if the thruster is part of a multi-component megastructure that includes concentric Dyson spheres forming a thermal engine, having a large ψ can result in the concentric spheres possessing poorer thermal efficiency.
The sheer size of Dyson spheres, Shkadov thrusters and other stellar engines inevitably makes us think about such constructions in the context of SETI, and whether we might be able to pick up the signature of such an object by looking at exoplanet transits. Richard Carrigan is among those who have conducted searches for Dyson spheres (see Archaeology on an Interstellar Scale ), but Forgan thinks a Shkadov thruster should also be detectable. For the light curve produced by an exoplanet during transit would show particular characteristics if a Shkadov thruster were near the star, a signature that could be untangled by follow-up radial velocity measurements.
The chances that we might pick up a transit showing clear signs of extraterrestrial engineering find the cheapest airline tickets seem remote, but Forgan's point is that we have numerous exoplanet surveys in progress, ranging from analysis of the Kepler data (with a recent SETI component factored in) to future surveys using the TESS and PLATO instruments, each intended to undergo radial velocity scrutiny as a follow-up to any detections. The GAIA satellite will also provide useful data for possible follow-ups of transit candidates. find the cheapest airline tickets With all this in the mix, Forgan wants to clarify what a Shkadov thruster would look like if by whatever chance we do find one in our data.
The presence of a Shkadov thruster, he demonstrates, can be flagged by study of the lightcurve of both transiting planet and thruster, with the possibility that both the primary and secondary eclipses can be affected. It would be a tricky catch even so, for transient phenomena like starspots can mask features in the lightcurve, and Forgan thinks that further radial velocity studies, find the cheapest airline tickets along with interferometric imaging and asteroseismology would have to come into play to tease out the features of such a thruster. Missions designed to study exoplanet atmospheres he mentions CHEOPS or EChO could be used to confirm the thruster's presence.
A long shot indeed, but it's good to have this study of those features that would flag a lightcurve as anomalous and indicative of advanced engineering. For while the probabilities of finding a Shkadov thruster are remote, we'll have a growing find the cheapest airline tickets number of datasets from various exoplanet missions find the cheapest airline tickets to draw on. Interstellar find the cheapest airline tickets archaeology find the cheapest airline tickets is all about digging into this rich stratum to see whether any observed events find the cheapest airline tickets fit models that suggest the presence of artificial objects. And today's exoplanet catalogue only hints at the volumes of information still to come.
The paper is Forgan, "On the Possibility of Detecting Class A Stellar Engines Using Exoplanet Transit Curves," accepted for publication in the Journal of the British Interplanetary Society ( preprint ). Leonid Shkadov's paper on Shkadov thrusters find the cheapest airline tickets is "Possibility of controlling find the cheapest airline tickets solar system motion in the galaxy, 38th Congress of IAF, October 10-17, 1987, Brighton, UK, paper IAA-87-613. More on stellar engines in coming find the cheapest airline tickets weeks.
Why not construct the mirror so that the reflected light is not reflected back onto the star, but past it? This would mitigate the effects of the reflected energy on the star, and increase thrust, nearly doubling it.
In the basic Shkadov thruster, asymmetric net light emission from the star exerts a direct thrust on it. But there must also be a net force as the star is attracted towards the mirror. find the cheapest airline tickets In my variant, it seems that only the gravitational attraction towards the mirror is in effect. What am I misunderstanding here?
I had known about the Shakodov find the cheapest airline tickets paper since 1990, and had a copy of the paper stashed find the cheapest airline tickets away, but had forgotten about it! It was your article, Paul, yesterday find the cheapest airline tickets that had me go dig it out. I might be misremembering by I think I called Greg Benford s attention to it in the 1990 s , but then again he may have known about it anyway.
The Zwicky stuff was new to me too, but I am not surprised , ol Fred was an out of box thinker, way out of the box! Predicting neutron stars in 1934 (tho I has to wonder if he knew of Chandrasekhar s calculation in 1930?)
The idea being , that when the Sun moves off the main sequence, or actually before it really reaches red giant , the Sun will be too hot for Earth habitation (less than a billion years) move the earth by using gravitational slingshots , trading momentum and energy with Jupiter. One has to use an almost 1000 km asteroid or Kuiper Belt object to move the Earth at a rate that keeps it in the habitable zone.
Would the thrust produced by such an arrangement be comparable to that of a more conventional solar sail? I often see a figure of 9 N per square kilometer in that regard, at 1 AU distance. Or, is the thrust not produced find the cheapest airline tickets directly by light-pressure, but through some other means related to reflecting the energy back onto the star s surface?
How close to the star s surface would the Shkadov thruster-mirror need to be positioned to work properly? I suppose the farther away it was, the wider the mirror would have to be to deflect the same amount of energy, and maintain gravitational equilibrium, but there would be a minimum distance at which the mirror could survive without melting.
One other thing just occured to me: Perhaps a system such as this could be adapted find the cheapest airline tickets for use with a black-hole Hawking Radiation thruster. The radiation involved would be more intense, but the physical dimensions of the system could be much smaller, too. And I imagine that a civilization capable of building a Shkadov thruster might be equally capable of securing or manufacturing a suitable black hole of relatively modest mass.
I m enjoying this series of posts, Paul advanced Type-II civilizations powerful enough and patient enough to move entire stars, it really captures the imagination. One can imagine steering our solar system to avoid dangerous close-encounters with other stars, or even transforming our entire planetary system into a giant generation ship on a slow trajectory to other parts of the galaxy.
Of course, the scale of engineering really boggles the mind. Inducing hot spots on a star with particle beams, building an enormous mirrored bowl over one half of the star to transform it into a photon thruster either of these schemes requires a civilization to learn to the energy and material resources of stars rather than mere planets.
I would like to ask, though, does anyone know the estimates of how long it would take to accelerate our sun by these methods, and what the travel time to various destinations would be? How long would it take to approach the Alpha C system by these means, for example? I imagine it would be slow, but with such a ship star your entire planet and civilization come with you for the ultimate generation ship!!
There seems to be an assumption that if yo