The researchers used astrometry which, like every method in cosmology, has a checkered past (and present - see Gliese 581g) regarding bold discoveries of previously unknown planets. In 1963, Peter van de Kamp of Swarthmore College's Sproul Observatory, announced that, based on his astrometry analysis, the faint, red star called Barnard's Star, six light years away and 20% of the mass of our Sun (and the largest angular motion across the sky) of any known star, had a planetary companion - and then two.
Other astronomers couldn't see any such changes in the motion of Barnard's Star, though, and his results were dismissed. The new work may rehabilitate astrometry a bit, though not van de Kamp's discovery(1) (for other methods of planet hunting, see Planet Hunters - How They Do It).
It is thus with some trepidation that we announce the candidate substellar companions orbiting either the primary or secondary stars in several binaries studied using dierential astrometry by PHASES - the Palomar High-precision Astrometric Search for Exoplanet Systems. Given that other astrometrically "discovered" sub-stellar objects have not withstood the test of continued observations,these may represent either the first such companions detected, or the latest in the tragic history of this challenging approach.
Compare that to headlines proclaiming that we have may found a "Star Wars" planet like Tatooine in the popular press - 1,960 of them!
Why did that catch on? To sell newspapers, I suppose. Planets that exist among two stars, like Tatooine in "Star Wars"(2), are not uncommon - a 2007 report said 40% of detected binary systems in one study had evidence of planets. What makes the difference is distance and size. Too far apart and the stuff that might make a planet just gets lost in space and if too close gas giants wouldn't be formed at all due to the gravity from competing stars.
The researchers say they may have hit on something interesting, though. They examined 51 binary systems, 33 with enough success to be valid, and they narrowed those to 15 after excluding systems with more than two stars, or ones that were to far apart, etc. It was HR 7162 that caught their attention, and the results mean, as they say in their paper, they were either very lucky or giant planets are more common than believed in binary systems.
To the researchers, it means gas giants may be formed by 'disk instability' rather than the more common 'core accretion' model cosmologists use, where clouds of debris and dust are shaped by the star's gravity. Instead, the gas giant that may exist at HR 7162 could have been formed due to its own gravity.
Given the disclaimer in the beginning about tiny errors in tiny signal, why did the researchers use astrometry in this instance? Like radial velocity (Doppler shift), astrometry can tell researchers mass but they say astrometry was able to let them analyze a wider range of stellar masses and rotational velocities and they believe it is just plain better than RV for binary stars.
So let's think about rethinking gas giant planet formation but keep your hype filter squarely in place as you read about this in the popular media - or just stick to reading Science 2.0
Citation: Matthew W. Muterspaugh, Benjamin F. Lane, S. R. Kulkarni, Maciej Konacki, Bernard F. Burke, M. M. Colavita, M. Shao, William I. Hartkopf, Alan P. Boss, M. Williamson, 'The PHASES Differential Astrometry Data Archive. V. Candidate Substellar Companions to Binary Systems', arXiv:1010.4048
NOTES:
(1) Though it likely inspired a resurgence in popular though about the "counter-Earth" hypothesis of Philolaus, that another Earth might be exactly opposite us on the other side of the Sun, as books like John Norman's "Gor" series set on Counter-Earth would appear a few years later. While the idea incorporated cosmological data at the time, its extrapolation that it must be true 'or nothing makes sense' is sophistry rather than science, so Dark Matter proponents should remain cautious.
(2) Yes, I said "Star Wars" and not "A New Hope" - I was there when it came out and there was no "episode" anything or "A New Hope" foolishness and, as you saw with later installments, he had no clue what he was doing outside one movie. Lucas also intended to kill off Darth Vader but the studio insisted they had him spin off into space in case it was successful and they wanted a sequel. So if you believe it was always called "A New Hope" you also believe, like Lucas, that a parsec is a unit of time, so go make the Kessel Run.
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