Astronomical Feature of the Month
Optically Imaged Star

    Astronomers have taken optical images of a brown dwarf orbiting near a Sun-like star, making it the closest object ever observed around a star through direct imaging. The distance between the brown dwarf and its parent star is less than that between the planet Uranus and the Sun. The observation is the latest in a flurry of star system discoveries made using new ground-based technology that in some cases generate sharper pictures than space telescopes. Brown dwarfs, middling objects between planets and stars, are considerably more massive than the largest planets but do not have enough mass to ignite the thermonuclear reactions necessary to become stars. This one, located 58 light-years away in the constellation Sagitta, contains more than 12 times the mass of all the planets in our solar system. Its parent star is roughly 2 billion years old, about half the age of our Sun. In recent years, dozens of distant planets have been found, but only through indirect means, such as observing the gravitational tug on their parent stars which only work within the first 4 astronomical units (AU) of a star system. The newly discovered brown dwarf is 14 AUs from its parent star, also known as 15Sge. Astronomers made the discovery using the Gemini North and twin Keck telescopes, which stand atop Hawaii's Mauna Kea. These observatories take advantage of the volcanic mountain's thin, clean and dry air by using adaptive optics to produce images with higher resolution than even the Hubble Space Telescope. Without the adaptive optics the brown dwarf would be too faint and too close to its parent star to be seen.

Image on left was taken in visible light with the light from Sacitta masked where the brown dwarf is. Image on right is a higher wavelength photo.