SDSS: An Oasis in the Brown Dwarf Desert

[bystander]

An Oasis in the Brown Dwarf Desert
Sloan Digital Sky Survey | 2016 Mar 31

[img3="The “before” and “after” comparison of the number of known brown dwarfs orbiting other stars. For each of the 41 close-in brown dwarf companions detected previously, the left panel shows the distance to its host star. The right panel shows the 112 brown dwarfs discovered in the new study. In both panels, the sizes of the brown dwarfs indicate their masses, and the circle shows the distance to Earth’s orbit. The larger dot (yellow or red) in the center of each panel represents the host star (not to scale). All the companions were discovered in different systems; they are shown together for comparison only. (Credit: N. Troup (UVirginia), SDSS)"]https://dl.dropboxusercontent.com/u/234 ... dwarfs.png[/img3][hr][/hr]

A new paper published this month in The Astronomical Journal by astronomers from the Sloan Digital Sky Survey (SDSS) reports a wellspring of new brown dwarf stellar companions, throwing cold water on the entire idea of the “brown dwarf desert,” the previously mystifying lack of these sub-stellar objects around stars.

Most stars in our Galaxy have a traveling companion. Often, these companions are stars of similar mass, as is the case for our nearest stellar neighbors, the triple star system Alpha Centauri.

Our Sun, of course, has companions of its own -- the planets of our solar system. Planetary companions are vastly different from stellar companions: they are much smaller, and they do not shine with their own light created through nuclear fusion. Even the largest planet in our solar system, Jupiter, would need to be 80 times more massive to even begin to shine this way.

Stuck in the middle are “brown dwarfs,” much bigger than Jupiter but still too small to be shining stars. These brown dwarfs give off merely a dim glow as they slowly cool. The universe is full of stars, and now we know that it is full of planets too. Astronomers expected that the universe would also be teeming with brown dwarfs.

But strangely, that’s not what they had been finding. Although astronomers have found plenty of brown dwarfs floating through space on their own, they found very few as stellar companions. Even in recent years, as new and sensitive detection techniques have allowed them to discover thousands of extrasolar planets, brown dwarfs have remained elusive -- in spite of the fact that they should be easier to find than planets.

In fact, until recently, so few brown dwarfs have been found orbiting close to other stars that astronomers refer to the phenomenon as the “brown dwarf desert.” This in turn created a problem for theorists, who have been scrambling to explain why astronomers have found so few. Therefore when SDSS astronomers started sifting through their data looking for brown dwarf companions to stars, they were hoping not to come up completely dry. ...

Companions to APOGEE Stars I: A Milky Way-Spanning Catalog of Stellar
and Substellar Companion Candidates and their Diverse Hosts - Nicholas W. Troup et al

• Astronomical Journal 151(3):85 (2016 March) DOI: 10.3847/0004-6256/151/3/85
  arXiv.org > astro-ph > arXiv:1601.00688 > 04 Jan 2016 (v1), 27 Feb 2016 (v2)

[bystander]

The Missing Brown Dwarfs
Leibniz Institute for Astrophysics, Potsdam | 2016 Apr 08

[c][attachment=0]nearest_26_BDs_2mass_sky_w3.jpg[/attachment][/c][hr][/hr]

When re-analysing catalogued and updated observational data of brown dwarfs in the solar neighbourhood, astronomers from Potsdam have found that a significant number of nearby brown dwarfs should still be out there, awaiting their discovery. The corresponding study by Gabriel Bihain and Ralf-Dieter Scholz from the Leibniz Institute for Astrophysics Potsdam (AIP) challenges the previously established picture of brown dwarfs in the solar neighbourhood.

Brown dwarfs are objects that are too large to be called planets, yet too small to be stars. Having a mass of only less than seven per cent of the mass of the Sun, they are unable to create sufficient pressure and heat in their interiors to ignite hydrogen-to-helium fusion, a fundamental physical mechanism by which stars generate radiation. In this sense brown dwarf are “failed stars”. It is therefore important to know how many brown dwarfs really exist in different regions of the sky in order to achieve a better understanding of star formation and of the motion of stars in the Milky Way.

Gabriel Bihain and Ralf-Dieter Scholz have taken a careful look at the distribution of nearby known brown dwarfs from a point of view that was not looked at before. To their surprise they discovered a significant asymmetry in the spatial configuration, strongly deviating from the known distribution of stars. ...

The scientists concluded that there should be many more brown dwarfs in the solar neighbourhood that are yet to be discovered and that will fill the observed gap. If they are right, this would mean that star formation fails significantly more often than previously thought, producing one brown dwarf for every four stars. In any case, it appears, the established picture of the solar neighbourhood and of its brown dwarf population will have to be rethought. ...

A non-uniform distribution of the nearest brown dwarfs - G. Bihain, R.-D. Scholz

• Astronomy & Astrophysics 589:A26 (May 2016) DOI: 10.1051/0004-6361/201528007
  arXiv.org > astro-ph > arXiv:1603.00714 > 02 Mar 2016

[neufer]

The Missing Brown Dwarfs
Leibniz Institute for Astrophysics, Potsdam | 2016 Apr 08

Brown dwarfs are objects that are too large to be called planets, yet too small to be stars. Having a mass of only less than seven per cent of the mass of the Sun, they are unable to create sufficient pressure and heat in their interiors to ignite hydrogen-to-helium fusion. In this sense brown dwarf are “failed stars”. The scientists concluded that there should be many more brown dwarfs in the solar neighbourhood that are yet to be discovered and that will fill the observed gap. If they are right, this would mean that star formation fails significantly more often than previously thought, producing one brown dwarf for every four stars.

[b][color=#0000FF]Emblem of the Galactic Republic[/color][/b]

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The _No Star Left Behind_ law requires all star clusters receiving Galactic Republic funding to administer a galactic arm wide standardized hydrogen-to-helium fusion test. Star clusters that receive Title I funding must make Adequate Millennial Progress (AMP) in their star formation test scores. If a star cluster's results are repeatedly poor, then steps are taken to improve the cluster.