Planets with two suns are more likely to thrive than planets with only one sun, according to a new study.
As revealed exclusively to BBC Sky at Night Magazine, the research suggests planets form more easily around double stars than single stars.
The study also shows that double stars have the conditions for enormous gas giant planets larger than Jupiter to form around them, but also that some planets may be gravitationally booted out of the system into deep space.
Double stars and planet formation
When stars form, they're left with a swirling disc of cosmic debris rotating around them.
These protoplanetary discs – or accretion discs – are made out of the leftover ingredients out of which the star itself formed.
Over time, chunks of the cosmic debris cling together via gravity, forming small pebbles that accrete more material over time, growing and growing to eventually become fully-formed planets in orbit around the star.
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The same process is thought to have occurred in our own Solar System, the planets, moons and asteroids that orbit the Sun forming from the dusty disc that surrounded our host star when it was still a stellar infant.
But what if, rather than one star, this planet-forming scenario occurred around a pair of stars orbiting each other?
Such systems – known as binary stars – are common throughout the Galaxy and, given the gravitational tug-of-war that occurs between the stars as they orbit one another, astronomers had previously considered them too chaotic to make planet formation occur easily.
Two suns better than one?
Astrophysicists from the University of Lancashire in the UK say planets may actually form more easily around double stars, rather than single stars
That could mean that a fictional world like Tatooine, Luke Skywalker's home planet in the Star Wars franchise, which features double sunsets, are more common in the Galaxy than once thought.
The research is published in the journal Monthly Notices of the Royal Astronomical Society (MNRAS).
The team behind the study used computer simulations to model the evolution of gas discs surrounding young binary stars.
They found that the inner regions discs around binary stars act as a sort of 'forbidden zone', where the chaotic effects of the gravitational to-and-fro make it unlikely that planet formation could occur.
But further out from the stars, the team say, the disc becomes a breeding ground for the formation of giant planets, fragmenting under its own gravity to produce multiple worlds.
"Close to a binary star it’s simply too violent for planets to form," says Dr Matthew Teasdale, who led the research as part of his PhD project.
"But move farther out and the disc becomes an ideal environment for planet formation."
"Binary stars were once seen as hostile environments for planet formation," says Dr Dimitris Stamatellos, who supervised the project.
"What we’re finding is that they can actually be extremely productive. Once you get past the danger zone, planets can form quickly and in large numbers."
Gas giants and rogue worlds
The team's simulations also reveal that discs around binaries may produce more planets through fragmentation than discs around single stars.
They found that a larger proportion of planets become gas giants, bigger even than Jupiter in our own Solar System.
And, the team say, some planets around binary stars can become victims of the strong gravitational forces at play, and may be ejected from the systems, flung outwards to become free-floating rogue planets drifting through space.
Key to the study is the finding that planets orbiting more than one star may be more common than previously thought.
The gravitational instability, where the dusty discs around the stars break apart under their gravity, could actually be important for planet formation.
The team say their results open up possibilities for future studies with powerful telescopes like the Atacama Large Millimeter/submillimeter Array in Chile, the James Webb Space Telescope and the upcoming Extremely Large Telescope.
"While planets may struggle to survive near their twin Suns, farther out these systems transform into dynamic planet-forming environments," Dr Stamatellos says, "suggesting that real-life Tatooines may be far less rare than we once imagined."
Read the full paper via the Monthly Notices of the Royal Astronomical Society
