An international team of astronomers using the worlds biggest telescopes have directly measured the mass of an ultra-cool brown dwarf star and its companion dwarf star for the first time. Barely the size of the planet Jupiter, the dwarf star weighs in at just 8.5 percent of the mass of our Sun. This is the first ever mass measurement of a dwarf star belonging to a new stellar class of very low mass ultra-cool dwarf stars. The observation is a major step towards our understanding of the types of objects that occupy the gap between the lightest stars and the heaviest planets.
This image shows the orbit of the brown dwarf around the ultra-cool L-dwarf. Each red dot on the orbit (in blue) corresponds to one observation made with a ground- or space-based telescope. The observations cover 60% of the whole orbit. Credit: ESA/NASA and Herve Bouy (Max-Planck-Institut für Extraterrestrische Physik/ESO, Germany)
Image credit: ESA/NASA and Herve Bouy (Max-Planck-Institut für Extraterrestrische Physik/ESO, Germany)
In 2000 the NASA/ESA Hubble Space Telescope detected a brown dwarf companion around the star named 2MASSW J0746425+2000321. In the subsequent four years the system was tracked by the NASA/ESA Hubble Space Telescope, the European Southern Observatory’s Very Large Telescope (Chile), the Gemini North (Hawaii) and the Keck Telescopes (Hawaii). The masses of the stars could be measured from the orbital motions of the two objects. With a mass of 8.5% of our Suns mass, the primary star is precariously close to the theoretical minimal fusion limit, which is 7.5 percent of our Suns mass. Objects below this limit are called brown dwarfs, failed stars or even super-planets, as their properties are more similar to those of large Jupiter-type planets than stars. The brown dwarf is measured to be 6.6 percent of the Suns mass, and thereby too puny to shine by nuclear fusion.
The mass measurements were made by an international team of astronomers led by Hervé Bouy from the Max-Planck-Institut für Extraterrestrische Physik/ESO, Germany and the Observatoire de Grenoble, France; Eduardo Martin (Instituto de Astrofisica de Canarias, Spain); and Wolfgang Brandner (Max Planck Institut für Astronomie, Germany).
Lars Christensen | ESA
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