Aliens may be piloting their stars through the galaxy - and we might be able to find them.
The idea of a solar engine itself dates back to 1948, when the astronomer Fred Zwicky - who co-discovered dark matter - suggested that advanced civilisations might be able to navigate the path of the entire solar system through the galaxy.
He proposed that by using massive 'bullets' made of nuclear fuel fired at the sun, it might be possible to create explosions able to propel stars through space - taking us and the other planets with it.
Discovery.com adds that in the late 1990s the idea was taken up by the physicist Leonid Shkadov, who said that using a massive spherical mirror radiation from the Sun could be reflected back onto its surface - causing a force that would push it through space.
Such devices might be necessary if a civilisation wanted to avoid the sun passing through a cold cloud of molecular hydrogen - which can cause serious climate change - or passage close to another star.
Needless to say, building such a device is far beyond any technology we can imagine.
But that's not to say that in the enormous variety of the galaxy, or beyond, someone hasn't managed it. And if they have, they might be leaving tell-tale signs behind that mean we might be able to find them.
NASA's Kepler Mission Discovers Planet
In this handout illustration made available on December 5, 2011 by NASA, the Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star is digitally illustrated. For the first time NASA's Kepler mission has confirmed a planet to orbit in a star's habitable zone; the region around a star, where liquid water, a requirement for life on Earth, could persist. The planet is 2.4 times the size of Earth, making it the smallest yet found to orbit in the middle of the habit. Clouds could exist in this earth's atmosphere, as the artist's interpretive illustration depicts. (Photo Illustration by Ames/JPL-Caltech/NASA via Getty Images)
NASA's Kepler Mission Discovers Planet
In this handout illustration made available on December 5, 2011 by NASA, a diagram compares our own solar system to Kepler-22, a star system containing the first 'habitable zone' planet discovered by NASA's Kepler mission. The habitable zone is the sweet spot around a star where temperatures are right for water to exist in its liquid form. Liquid water is essential for life on Earth. The diagram displays an artist's rendering of the planet comfortably orbiting within the habitable zone, similar to where Earth circles the sun. Kepler-22b has a yearly orbit of 289 days. The planet is the smallest known to orbit in the middle of the habitable zone of a sun-like star and is about 2.4 times the size of Earth. (Photo Illustration by Ames/JPL-Caltech/NASA via Getty Images)
Extrasolar Planet HD 209458 b, Osiris
Artist's conception released by NASA of extrasolar planet HD 209458 b, also known as Osiris, orbiting its star in the constellation Pegasus, some 150 light years from Earth's solar system. Scientists have used an infrared spectrum -- the first ever obtained for an extrasolar planet -- to analyze Osiris' atmosphere, which is said to contain dust but no water. The planet's surface temperature is more than 700 Celsius (1330 Fahrenheit).'
Planet & Its Parent Star
Picture released 04 October 2006 by the European Space Agency shows an artist's impression of a Jupiter-sized planet passing in front of its parent star. Such events are called transits. When the planet transits the star, the star's apparent brightness drops by a few percent for a short period. Through this technique, astronomers can use the Hubble Space Telescope to search for planets across the galaxy by measuring periodic changes in a star's luminosity. The first class of exoplanets found by this technique are the so-called 'hot Jupiters,' which are so close to their stars they complete an orbit within days, or even hours. A seam of stars at the centre of the Milky Way has shown astronomers that an entirely new class of planets closely orbiting distant suns is waiting to be explored, according to a paper published 04 October 2006. An international team of astronomers, using a camera aboard NASA's Hubble telescope, delved into a zone of the Milky Way known as the 'galactic bulge', thus called because it is rich in stars and in the gas and dust which go to make up stars and planets. The finding opens up a new area of investigation for space scientists probing extrasolar planets - planets that orbit stars other than our own. AFP PHOTO NASA/ESA/K. SAHU (STScI) AND THE SWEEPS SCIENCE TEAM
Picture released 04 October 2006 by the European Space Agency shows an artist's impression of a unique type of exoplanet discovered with the Hubble Space Telescope. This image presents a purely speculative view of what such a 'hot Jupiter' (word dedicated to planets so close to their stars with such short orbital periods) might look like. A seam of stars at the centre of the Milky Way has shown astronomers that an entirely new class of planets closely orbiting distant suns is waiting to be explored, according to a paper published 04 October 2006. An international team of astronomers, using a camera aboard NASA's Hubble telescope, delved into a zone of the Milky Way known as the 'galactic bulge', thus called because it is rich in stars and in the gas and dust which go to make up stars and planets. The finding opens up a new area of investigation for space scientists probing extrasolar planets - planets that orbit stars other than our own. AFP PHOTO NASA/ESA/K. SAHU (STScI) AND THE SWEEPS SCIENCE TEAM
The Goldilocks Planet: Glises 581 G
Scientist have found a new potentially habitable planet.
Imagining Extrasolar Planets
From the Spitzer Science Center. While astronomers have identified over 500 planets around other stars, they're all too small and distant to fill even a single pixel in our most powerful telescopes. That's why science must rely on art to help us imagine these strange new worlds. From Spitzer Space Telescope. Even without pictures of these exoplanets, astronomers have learned many things that can be illustrated in artwork. For instance, measurements of the temperatures of many "Hot Jupiters," massive worlds orbiting very close to their stars, hint that their atmospheres may be as dark as soot, glowing only from their own heat. While "Hot Jupiters" would be relatively dark in visible light, compared to their stars, their brightness is proportionally much greater in the infrared. Illustrating this dramatic contrast change helps explain why the infrared eye of NASA's Spitzer Space Telescope plays a key role in studying exoplanets. As our understanding evolves, so must the artwork. Astronomers found a blazing hot spot on the exoplanet Upsilon Andromedae b that at first, appeared to face towards its star. More data has revealed that the hottest area is actually strangely rotated almost 90 degrees away, near the day/night terminator. WASP 12b is as hot as the filament in a light bulb, and would be blazing bright to our eyes. Most interestingly, if it proves to have a strongly elliptical orbit, as first thought, calculations show it would be shedding some of its outer atmosphere <b>...</b>
Now in a paper by Duncan H. Forgan at the University of Edinburgh, published in the Journal of the British Interplanetary Society, we have an idea of how to do exactly that.
Forgan proposes that a 'mega mirror' of the scale required to pilot a star would partially obscure the disk of a distant sun. And when scientists look for the transit of planets across those stars - as they do when looking for exoplanets with the Kepler space telescope - the resultant light curve would be distinctive. By looking for the right kind of light curve, it might be possible to find evidence of these megastructures - and thus aliens powering themselves across space.
In the paper Forgan goes on to model how those light curves look, and how the properties of the thruster can be identified in the data.
Alas, Forgan does admit that "even given optimistic assumptions" the chance of finding such a mirror "remains stubbornly low".
"Despite this, many exoplanet transit surveys designed for radial velocity follow-up are on the horizon, so we argue that this remains a useful serendipitous SETI technique. At worst, this technique will place an upper limit on the number of Class A stellar engines in the Solar neighbourhood; at best, this could help identify unusual transiting exoplanet systems as candidates for further investigation with other SETI methods."
However, thanks to the data of 150,000 stars in the constellation Cygnus gathered by Kepler so far, this theory is at least testable. So there is a chance - albeit a very, very small one - that we might just be able to find something extraordinary in the darkness.