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Beyond Earthly Skies

Observations of a Low-Gravity Brown Dwarf

28 Jul 2014, 22:00 UTC
Observations of a Low-Gravity Brown Dwarf
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Brown dwarfs occupy the mass range between the most massive planets and the least massive stars. They are not massive enough to sustain hydrogen fusion in their cores and so they cool gradually with time. As a brown dwarf cools, it contracts, evolving from a low to a high “surface” gravity. The word “surface” is shown in quotation because a brown dwarf does not have a solid surface. Instead, a brown dwarf’s “surface” simply refers to its observable photosphere. Brown dwarfs are gaseous throughout. They are primarily composed of hydrogen and helium, with trace amounts of heavier elements.Figure 1: Artist impression of a brown dwarf that is still glowing red-hot from heat acquired during its formation.For a young brown dwarf that has yet to cool and contract to its final radius, it can display low-gravity features that can be identified from observations in the near-infrared waveband. This is because the low-gravity atmosphere of a young brown dwarf drives the formation of thicker than normal clouds in the brown dwarf’s photosphere. The thicker clouds give rise to a redder near-infrared spectrum because shorter wavelength light (i.e. bluer light) is attenuated and scattered by clouds more than longer wavelength light (i.e. redder ...

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