The leading planetary formation theory posits that planets grow from the agglomeration of smaller bodies, such as asteroids. Over millions of years, the planet gains mass as its gravitational field starts to pull in more and more dust, asteroids and other junk. However, this mechanism cannot be applied to HD 106906b -- at that orbital distance, this process acts slowly, making a planet of 11 Jupiter masses an impossibility.
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A second theory could be invoked: Did HD 106906b rapidly form from the rapid gravitational collapse of a knot of material in the star's protoplanetary disk? Again, this mechanism is more likely to occur very close to the host star where plentiful material can be found; at 650 AU there would be little material to trigger the collapse.
So, according to Bailey, that leaves only one explanation. But there's a problem with that one, too.
"A binary star system can be formed when two adjacent clumps of gas collapse more or less independently to form stars, and these stars are close enough to each other to exert a mutual gravitation attraction and bind them together in an orbit," said Bailey in a UA news release. "It is possible that in the case of the HD 106906 system the star and planet collapsed independently from clumps of gas, but for some reason the planet's progenitor clump was starved for material and never grew large enough to ignite and become a star."