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from the still-leaves-a-lot-of-exoplanets dept.
Over half of the gas giant "exoplanets" spotted by the Kepler telescope may actually be explained by other astrophysical phenomena, such as binary stars and brown dwarf stars:
It's always exciting when Kepler discovers a new exoplanet, and it's generally assumed that there is a relatively low chance of a false positive. But according to a new study, there may be a much higher rate of false positives than we thought with regard to gas giants, possibly up to 55%.
In the study, astronomers from Instituto de Astrofísica e Ciências do Espaço examined a sample of 129 gas planets detected by Kepler through the transit method. The transit method involves extrapolating the existence of a planet from the periodic dimming of a star's light emission that is presumably caused by an exoplanet's orbit. They found that approximately half of them weren't planets at all; rather, the light's dimming was caused by some other astrophysical phenomenon.
Gas giants are particularly vulnerable to false positives, as they can easily be imitated by eclipsing binaries. Eclipsing binaries are binary star systems aligned with the observer's (in this case, Kepler's) line of sight, which causes the larger star to block the light from the smaller. The researchers found that 52.3% of the gas giants were actually eclipsing binaries, while 2.3% were brown dwarfs, or a "failed star" between gas giants that doesn't have enough mass to fuse hydrogen to its core.
Also at the Institute of Astrophysics and Space Sciences.
(Score: 0) by Anonymous Coward on Friday December 04 2015, @09:07AM
What's the difference between a gas giant and a "failed star"?
(Score: 2) by sudo rm -rf on Friday December 04 2015, @01:06PM
Depends on who you ask. Some say a "failed star" or brown dwarf has experienced fusion in its core at one time in its past, while a gas giant has not. What kind of fusion depends on the mass, but that's only relevant for sub-classification of the body (spectral sequence).
In this [berkeley.edu] [pdf] paper from 2008, the author Adam J. Burgasser (assistant professor of physics at the Massachusetts Institute of Technology in Cambridge) tells us:
a) Brown dwarf vs. star
For objects with mass less than about 0.072 M� [that is solar masses, I don't know if the glyph is posted correctly], degeneracy pressure halts contraction before the critical H fusion temperature is reached. Hydrostatic equilibrium, but not thermal equilibrium, is achieved. Such “failed stars” are brown dwarfs.
and b) Brown dwarf vs gas giant (planet)
The distinction between hydrogen-fusing stars and brown dwarfs is well defined. But what distinguishes brown dwarfs from planets, given their similar sizes and atmospheric properties? Astronomers vigorously debating that semantic question fall mainly in two camps. One advocates a definition based on formation—a brown dwarf condenses out of giant molecular clouds, whereas a planet forms via core accretion in a circumstellar debris disk. The other focuses on interior physics: A brown dwarf must be heavier than the mass threshold for core fusion of any element, roughly 13 Jupiter masses, or 0.012 M�. Pluto’s recent demotion has focused attention on the ambiguity of the term “planet” in the solar system. Brown dwarfs are forcing us to reexamine a related ambiguity in a galactic context.
(Score: 0) by Anonymous Coward on Friday December 04 2015, @02:16PM
Alright, so
0.003 Jupiter = rocky planet
0.05 Jupiter = ice giant planet
?? < 1 Jupiter -- 13 Jupiter = gas giant planet
13 Jupiter -- 78 Jupiter = brown dwarf (failed star)
78 Jupiter -- ?? = succesful star
1000 Jupiter = the Sun
20000 Jupiter = Deneb
(Score: 2) by takyon on Friday December 04 2015, @05:13PM
That looks right. Apparently there is a little more going on [wikipedia.org] above 60-65 Jupiter masses.
They can fuse lithium above 65 Jupiter masses:
The presence of lithium is a good test for whether a heavier object is a brown dwarf and not a low-mass star:
But they could be too cool to fuse lithium:
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]
(Score: 0) by Anonymous Coward on Friday December 04 2015, @09:13PM
Goatse and Paris Hilton?
Or is one of those a dwarf planet? hmm. Well at least Paris's stardom is gone.