The Keck II laser guide star (LGS) system has proven particularly adept in locating and studying mysterious objects called brown dwarfs. Brown dwarfs never grew large enough or hot enough to sustain the hydrogen-helium fusion process that powers all stars, including our Sun. The brown dwarfs observed to date have been far more massive than even the largest planet in our solar system, Jupiter. However, these celestial bodies share many characteristics with large, gaseous planets like Jupiter. “They are basically intermediate steps between stars and giant planets. In some sense, Jupiter could be considered a very, very small brown dwarf,” explains Michael Liu, of the University of Hawaii’s Institute for Astronomy (IFA).

Using the LGS, Liu and his IFA colleagues have begun to make key brown dwarf discoveries that could help explain the physical properties of low-temperature atmospheres found in both brown dwarfs and large planets outside our solar system. “Before the laser guide star, in most cases, we couldn’t take images of them because brown dwarfs are too faint,” explains Liu. Brown dwarfs emit millions of times less light than the faintest star visible to the human eye. In the fall of 2005, Liu used the LGS to observe a unique pair of brown dwarfs orbiting each other. Also called binary brown dwarfs, this phenomenon is not unusual. However, in the brown dwarf pair that Liu identified, the infrared (heat) imagery from the Keck telescope depicted one dwarf with a bluish-purple atmosphere, and the other with a reddish atmosphere.

The reddish appearance, Liu believes, indicates that the brown dwarf has an atmosphere of metallic clouds, containing mostly iron. Explains Liu, “It’s known that these clouds go away, but it’s not known how. We have never seen anything like this before. Understanding what clouds might look like around other planets is difficult for theorists. By studying how clouds form on brown dwarfs, we might learn how clouds form on other extra-solar planets. Even though the compositions are different, some of the processes might be the same.”

Michael Liu, Ph.D., received his doctorate from the University of California-Berkeley. He was formerly a Beatrice Watson Parrent Fellow at IFA. He then served as a Hubble Fellow at IFA before joining the tenure-track faculty at UH. His research focuses on brown dwarfs and extra-solar planets, as well as astrobiology. His work is supported by NASA, the National Science Foundation, and the Alfred P. Sloan Foundation.

Photos: (all-sky) WM Keck Observatory; (binary star) Michael Liu, University of Hawai'i