There is a cosmic limit to life on Earth, as our Sun steadily brightens throughout its life on the main sequence before bulging into a red giant.
Yes, that will happen to our solar system in the future, but this planet-destroying phase of the red giant will only begin in about 5 billion years
So a natural question might be what we might do in the distant future to try to keep our world habitable.
Various high-concept proposals have been put forward, including a carefully orchestrated program that would sling asteroids past Earth to launch the planet into a more distant orbit as the Sun brightens, using the same physics as the gravitational slingshot method of propelling space probes is used.
Matthew Scoggins and David Kipping, both at Columbia University’s Department of Astronomy in New York, have explored another high-tech, ultra-long-term possibility.
One way for an advanced civilization to counteract the brightening of their star as it ages is to gradually drain mass from it, thereby slowing the rate of fusion reactions at its core.
Scoggins and Kipping call such artificial suns “Lazarus Stars” after the biblical figure who rose from the dead.
Although they note that this “star-lift” method was proposed by David Criswell way back in 1985, the authors actually did the numerical calculations here to work out exactly what would be required.
How to remove earth from the sun
So could this be done? The astronomers considered two slightly different scenarios.
The first keeps the Sun at a constant brightness, or isoluminosity, by removing mass from it and then storing it in orbit between Earth and the Sun.
The second approach keeps the same amount of sunlight falling on Earth — isoradiation — by first removing less solar mass, but then ejecting it from the solar system, causing the planet’s orbit to also drift outward with the reduced gravitational pull.
Scoggins and Kipping calculate that changing the planet’s orbit using the isoirradiance approach can extend the Sun’s main-sequence lifetime – and thus the potential for life on Earth – by about 6 billion years.
To do this, a solar mass would have to be increased every year that corresponds to 2% of that of the largest asteroid, Ceres.
The isoluminosity approach, which stores the removed mass, would require more removal first, but could add 10 billion years to life on Earth.
Such a cosmic engineering project would require tremendous amounts of energy – the equivalent of 10 billion times the current annual energy consumption of our entire global civilization.
The isoirradiation method would take 100 times more to eject the material from the solar system.
But as the researchers point out, the sun itself is a tremendous source of energy, and an advanced civilization would only need to capture 0.03% of its annual production to power such an exercise.
While not attempting to speculate on what sort of advanced technology this sort of stellar engineering might enable, this study offers a fascinating glimpse into what the distant future of humanity might hold in store.
More like that
Lewis Dartnell read Lazarus Stars: Numerical studies of stellar evolution using star lifting by Matthew Scoggins and David Kipping. Read it online at: arxiv.org/abs/2210.02338.
This article originally appeared in the December 2022 issue of BBC Sky at Night Magazine.
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