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Stars

Brown Dwarfs

Brown dwarfs are objects so low in mass that their central temperatures never became high enough to ignite nuclear fusion reactions. Objects smaller than 0.05 MSun, and these include giant planets, generate no nuclear energy, and so are not luminous. However, they produce a small amount of gravitational energy since they are very slowly contracting. The core of Jupiter, for example, contracts a few millimeters per year. This giant planet, with a mass of about one thousandth that of the Sun, actually radiates in the infrared about 50% more energy than it receives from the Sun. After decades of searching,
Brown Dwarf astronomers discovered the first definite brown dwarf in 1995. Now, a new analysis of Hubble Space Telescope data implies our galaxy has almost as many of these failed stars as it does normal stars like the Sun. Several brown dwarfs probably lurk unseen within just 12 light-years of the Sun. This volume of space contains more than two dozen main sequence stars like the Sun — but only two known brown dwarfs. Both these brown dwarfs orbit the orange dwarf star Epsilon Indi, which is 11.8 light-years from Earth. They are the closest known brown dwarfs to the Sun. Figure 08-06 shows an artist's conception on the relative size of a hypothetical brown dwarf-planetary system and the solar system.

Figure 08-06 Brown Dwarf [view large image]

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