A new study has found that giant planets can form more easily around two young stars than around one.
Beyond the violent inner region, paired stars help fresh gas collapse into more giant-planet seeds in areas where slower planet formation would normally struggle.
Evidence beyond turbulence
Inside computer-made gas disks, outer regions around paired stars produced clusters of young planet-sized bodies.
At the University of Lancashire, astrophysicist Dr. Matthew Teasdale traced those bodies to disk fragments collapsing under gravity.
In the single-star and paired-star tests, wider stellar pairs stirred their disks sooner, and cooler realistic disks produced more young planet-forming bodies.
That pattern turns an old worry on its head for planet hunters, but only beyond the region where two stars pull too hard.
Why paired stars matter
About half of sun-like stars live with stellar partners, a long-running survey of nearby systems found.
Astronomers call these systems binary stars, meaning two stars locked in orbit around a shared center.
Their gravity does not simply stir the gas; it can also help dense patches collapse faster.
For planet formation, the same tug that destroys order near the middle can organize material farther out in the disk.
Planets with two suns
Worlds that circle both stars are circumbinary planets, a term for planets orbiting a stellar pair.
When astronomers confirmed Kepler-16b in 2011, a Saturn-sized world orbiting two stars, the idea became real.
The NASA Exoplanet Archive, which gathers confirmed worlds from NASA missions and research teams, now tracks thousands of planets around other stars.
Against that backdrop, finding more than 50 two-star planets no longer looks like a cosmic fluke, especially on wide orbits.
The forbidden center
Close-in orbits around a binary system have a well-known stability limit.
Gravity from two stars changes direction as they orbit, pulling nearby dust and gas into crossings that stop steady growth.
“Close to a binary star it’s simply too violent for planets to form,” said Teasdale.
Beyond roughly 50 astronomical units – about 4.6 billion miles from the stars – the modeled disks calmed enough for gravity to split them.
How giant planets grow
Farther from the paired stars, gravitational instability – gas becoming heavy enough to collapse under its own pull – took over.
Dense patches broke away from the disk, forming protoplanets – young bodies still feeding on nearby gas.
Because the outer disk stayed cooler, many starting masses fell near one to four times Jupiter’s mass.
Continued feeding can still push some bodies toward brown dwarfs, failed-star objects too heavy for planets but too small for star-like fusion.
The numbers tell a story
Across all simulations, the team produced 341 protoplanets in disks around single stars and stellar pairs.
Realistic paired-star disks made about nine protoplanets per disk, compared with 7.5 in single-star disks.
By final mass, about 71% of the realistic paired-star objects stayed in the planetary range.
Those figures matter because more starting bodies leave less gas for each one, making planet-sized endings more likely before they grow too massive.
Some worlds escape
Crowded young systems also threw some bodies away, creating free-floating planets – worlds that are no longer orbiting stars.
Out of 341 protoplanets, 13 escaped the modeled systems, an overall ejection rate near 4%.
Tighter and more stretched-out stellar pairs caused more close encounters, which gave small bodies escape speed.
Those castoffs left at roughly 1 to 4 miles per second, fast enough to drift between stars for millions of years.
Limits of the planet simulations
Most simulated survivors ended up near 100 astronomical units, or about 9.3 billion miles from their stars.
Observed two-star planets cluster both close to their stars and far away, partly because planet-hunting methods are better at spotting certain orbits.
The model did not produce close-in planets because it tested stellar pairs separated by 465 million to 930 million miles.
That boundary keeps the result useful, but it shows close-in circumbinary planets likely need tighter stellar pairs or later migration.
Future research directions
Computer models simplify real systems, even when they track gas, gravity, heating, and repeated close encounters.
The simulations ended after 70% of each disk’s material fell onto stars or young bodies.
Later movement after formation through gas or gravity could move planets inward, outward, or out of the system after the model stopped.
Future observations of young paired-star disks can test whether the brief bright phase appears where the simulations predict during observing campaigns.
Instead of blocking planet birth, paired stars can carve a violent center while helping outer gas make giant worlds.
Future searches will test how often that pathway works, especially for planets that orbit far from both stars.
The study is published in the journal Monthly Notices of the Royal Astronomical Society.
Image Credit: Center for Astrophysics | Harvard & Smithsonian
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