Brown dwarf

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The brown dwarf Gliese 229B next to the star Gliese 229 itself. The left image has been made by the ground based telescopes in the Palomar Observatory, the right one is from Hubble. This was the first confirmed brown dwarf discovered.[1]

Brown dwarfs are a class of "sub-stellar" objects that have mass that is above the range of mass of gas giant planets, but not enough for their cores to sustain nuclear fusion of hydrogen-1 and turn them into proper stars. That's why they are often described as "failed stars".

The upper limit of a brown dwarf mass is about 75 and 80 times the mass of Jupiter (for comparison, the Sun is considered to be a "yellow dwarf" and it's about 1000 times the mass of Jupiter). The lower limit that distinguishes them from gas giants is less clear, but it's considered to be around 13 times the mass of Jupiter. Anything above the lower limit fuses deuterium (hydrogen-2), and anything above about 65 times the mass of Jupiter fuses lithium.

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[edit] Woo

In various versions of the Planet X/Nibiru story, it is claimed to be either a brown dwarf or to orbit around one. In the somewhat bizarre post-Velikovsky Saturn scenario, Saturn was supposed to have been a brown dwarf, and Earth was in orbit around it within human memory, in a perpetual 'purple twilight'.

[edit] Visibility

Planet X/Nibiru proponents like to claim that brown dwarfs are "invisible" and can be detected only in infra-red light, and this is why no astronomers, amateur or professional, have been able to spot the "incoming" Planet X/Nibiru. The claim is partially true:

  • brown dwarfs fuse deuterium, which heats them up and everything heated emits infra-red light (and if it's hot enough, visible light too: think of red-hot iron, or see Planck's law[wp] at Wikipedia);
  • small brown dwarfs may be cold enough to emit mostly infra-red light;
  • thus, if we consider only light emission, a small, cool brown dwarf will be fainter in the visible spectrum and brighter in the infra-red spectrum.
  • light sources become fainter with distance, so if a brown dwarf is far away enough, its visible light may be too faint to be detected by the human eye or a telescope, while its infra-red light may be still above the threshold of detection.

That doesn't mean that brown dwarfs are "invisible", though. A brown dwarf is at least the size of Jupiter or larger and will reflect light in the same way. If one was close to our Solar System (or in it, as some claim), it would look like Jupiter at the same distance due to reflected sunlight. A brown dwarf inside the orbit of Jupiter would be as bright as or brighter than Jupiter in the night sky. (And Jupiter is one of the brightest objects in the night sky after the Moon, Venus and the International Space Station.)

More importantly, though, we've launched space telescopes (such as IRAS and WISE) designed explicitly to observe the sky in the infrared spectrum. An object that emitted only infrared radiation should still have been detected by one of these telescopes.

[edit] External links

  • Brown dwarf article at Wikipedia, if you are interested in more details

[edit] Footnotes

  1. http://hubblesite.org/newscenter/archive/releases/1995/48/text/
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