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Tag Archives: brown dwarf

From an article on the Sky and Telescope website by Monica Young, originally posted on December 10, 2015.

More than half of the potential giant planets detected by NASA’s Kepler satellite might not be planets after all according to a study by Alexandre Santerne (University of Porto, Portugal, and Aix Marseille University, France). A press release following the Extreme Solar Systems III conference in Hawaii summarized the study with the headline: “Half of Kepler’s Giant Exoplanet Candidates are False Positives.”

Common-False-Positives-480

Credit: NASA/Ames Research Center

Santerne and colleagues followed up on Kepler’s long list of planet candidates during a five-year observing campaign. Between July 2010 and July 2015, the team spent 370 nights observing 129 planet candidates out of more than 4,000 that were identified by Kepler, and only 45 of these turned out to be bona fide planets. The rest fell into 3 different categories: 3 were brown dwarfs, 63 were multiple-star systems, and 18 were neither of these, but could not be confirmed as planets. Even if all of those 18 cases turned out to be planets, 51% of Kepler’s giant potential planets would still turn out not to be real.

Previous studies found a much lower ‘false-positive’ rate for Kepler’s planet candidates. However, according to experts on Kepler data, this seemingly surprising high false-positive rate is not surprising at all.

For more information on our Solar System, and others, see Chapter 9 of The Cosmos. Link to the original article here.

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Astronomers have used data from the Spitzer Space Telescope to measure the distances, and hence temperatures, of so-called “brown dwarfs” (see Section 9.5).

These brown dwarfs, the coldest known free-floating celestial bodies, were found to be warmer than previously thought, with surface temperatures ranging from about 250 to 350 degrees Fahrenheit (125 to 175 degrees Celsius). By comparison, the Sun has a surface temperature of about 10,000 degrees Fahrenheit (around 6000 degrees Celsius).

To reach these surface temperatures after cooling for billions of years, these objects would have to have masses of only 5 to 20 times that of Jupiter. Unlike the Sun, the only source of energy for these coldest of brown dwarfs is from their gravitational contraction, which depends directly on their mass. The Sun is powered by the conversion of hydrogen to helium; these brown dwarfs are not hot enough for this type of “nuclear burning” to occur.

PIA17258_ip

Credit: NASA/JPL-Caltech

The findings help researchers understand how planets and stars form, but also present new puzzles to astronomers who study cool, planet-like atmospheres, as the observable properties don’t correlate with temperature in a straight-forward way. Ongoing studies of newly discovered brown dwarfs may shed some light (and heat) on these outstanding issues.

Read the JPL press release for more detail and additional images.