Could We Move The Sun?

An idea that really captures my imagination is what kinds of future civilizations there might be. And I’m not the only one. In 1964, the Soviet astronomer Nikolai Kardashev defined the future of civilizations based on the amount of energy they might consume.

A Type I civilization would use the power of their entire planet. Type II, a star system, and a Type III would harness the energy of an entire galaxy. It boggles the mind to think about the engineering required to rearrange the stars of an entire galaxy.

Is it possible to move a star? Could we move the Sun?

This idea was first proposed by physicist Dr. Leonid Shkadov in his 1987 paper, “Possibility of controlling solar system motion in the galaxy”.

Here’s how it works.

A future alien civilization would construct a gigantic reflective structure on one side of their star. Light from the star would strike this structure and bounce off, pushing it away.

If this reflective structure had enough mass, it would also attract the star with its gravity.
The star would be trying to push the structure away, but the structure would be pulling the star along with it.

If a future civilization could get this in perfect balance, it would be able to “pull” the star around in the galaxy, using its own starlight as thrust. At first, you wouldn’t get a lot of speed. But by directing half the energy of a star, you could get it moving through the galaxy.

Over the course of a million years, you would have changed its velocity by about 20 meters/second. The star would have traveled about 0.3 light years, less than 10% of the way to Alpha Centauri. Keep it up for a billion years and you would be moving a thousand times faster. Allowing you to travel 34,000 light years, a significant portion of the galaxy.

Imagine a future civilization using this technique to move their stars to better locations, or even rearranging huge portions of a galaxy for their own energy purposes.

This may sound theoretical, but Duncan Forgan, from the University of Edinburgh suggests a practical way to search for aliens moving their stars. According to him, you could use planet-hunting telescopes like Kepler to detect the bizarre light signatures we’d see from a Shkadov Thruster. There’s nothing in the laws of physics that says it can’t happen.

It’s fun to think about, and gives us another way that we could search for alien civilizations out there across the galaxy.

Related articles:
Detecting a Class A Shkadov Thruster
Shkadov Thrusters and Stellar Engines

20 Replies to “Could We Move The Sun?”

  1. While I appreciate the thought experiment, the thoughts behind the Russian’s thought experiment are more intriguing to me. Any civilization wanting so much energy is extremely inefficient in its use. As is moving a whole star to get somewhere else within the galaxy even were it economically possible to build such a structure. I postulate that the relative sparsity of our part of the galaxy is to our advantage. We gain perspectives we could not were we located in a higher density neighborhood filled with stellar light pollution.

    1. “Any civilization wanting so much energy is extremely inefficient in its use”
      Had to laugh, thinking about horse whips and buggies…! We just don’t know what could be done with these quantities of energy. Peter F. Hamilton has offered a few ideas, as have others; let’s keep an open mind?

  2. Ok, so why would you bother moving a star?!
    C’mon Universe Today, this is kinda of a pointless article.

      1. there’s many reasons to move the star. to save ourselves from an undesireable galactic collision is a real one. but any reason to move the earth — which would be pointless without the sun.

      2. Collisions between galaxies are unlikely to affect the solar system, as the distances between stars are so great. Any disaster that could happen to our solar system is probably going to be hard to predict millions of years ahead of time, which is the sort of timescale involved with this method. Any civilization able to build a giant mirror like this will also be able to build enormous mobile space habitats and evacuate their home planet, much easier than trying to move their star out of harm’s way.

        Then there’s the problem of what the mirror would do to the home planet anyway. Its gravitational influence would affect the planet’s orbit, probably not for the better. There will be periods when the mirror shines directly onto the planet, illuminating it with effectively a second sun, and if the planet orbits outside the orbit of the mirror there will be eclipses as well. This would give the planet periods of extreme heat and cold. It’s probably possible to engineer a workaround for this problem, but the idea has so many drawbacks already.

      3. We have survived many such collisions already. That they would make stars collide are unlikely, and what better proof than our continued existence?

      4. It might be helpful to use this technology to move the Earth, for example, when the sun swells up into a red giant, we would need to move the Earth to preserve its atmosphere (of course, we’ll all be long dead by then and evolved into some other creature long before that happens, although only if we don’t destroy the planet in the mean time).

  3. How big is gigantic? To build a gigantic structure that is massive enough to exert enough of a gravitational pull on the sun for moving it around in the galaxy would most likely require much more material than there is on all the terrestrial planets in the solar system combined (about two earth masses).

  4. A much, much smaller (less massive) version could be used to move the Earth. As the sun ages it gets hotter. Depending on whose model you believe within maybe 400 million years Earth will be too hot for land life. Move it. Just don’t aim the reflector at the Earth by mistake.

    1. The “Shkadov Thruster” can only be used to move a star. The Earth doesn’t radiate the necessary energy.

      1. Not so. The sun provides the radiant energy to the “smaller” less massive reflector located near the Earth. This structure need be massive enough to gravitationally attract the Earth gradually to move its orbit. This reflector could be many orders of magnitude less massive than one needed to move a star. Further out from the sun near Earth orbit there is far less radiant energy which works against this scheme.

  5. so instead of aliens arriving here in spaceship, they could bring their entire solar system.

  6. A structure like that would require massive amounts of unobtanium.

    I thought this was a science site.

  7. “and a Type III would harness the energy of an entire galaxy.”

    I don’t know what Kardashev was thinking. The universal speed limit prohibits all economies between stars (except possibly information barter) up to and including energy transfer.

    A loose knit “civilization” of individual colonies that are just slowly diverging would rather constitute type II Dyson swarms at beast. (I.e. using Oort cloud material to englobe the local star for capturing its energy.)

  8. Moving the sun would cause havoc with all of the planets’/asteroids’ orbits and it is unlikely to ever be practical, possible or desirable.

  9. I really doubt these hyper-energy civilizations exist. With ETI I prefer to use the term collective, because they may organize themselves in means totally different from what we call civilization. However, things like ring worlds, Dyson spheres and other extreme ideas I doubt exist anywhere, ever did exist or ever will.

    Any intergalactic system of self-replicating IGUS that might come about are from von Neumann probes that have the ability to utilize interplanetary resources and which over time begin to migrate to other stars and throughout the galaxy. These might evolve and become more intelligent in some cases over time.

    That aside, I agree that it seems futile and pointless to move a star. I would say what might make a bit of sense is generating stars. A colossal Bussard ramjet could be used as a sort of hydrogen snow plough to accumulate enough material that it gravitationally implodes into a star. I doubt that any ETI are actually doing this, or ever will, but at least I can see some purpose for it.


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