A microlensing event has revealed an elusive brown dwarf. Discovery of the new brown dwarf star was made possible by a unique collaboration between NASA’s Spitzer and Swift space telescopes.
Microlensing is a phenomenon whereby an objects in space, often invisible to the eyes of astronomers, are revealed by the magnification caused by the gravitational field of one or more objects situated between the elusive object and the lens of a telescope.
The discovery of this brown dwarf, with the unwieldy name OGLE-2015-BLG-1319, marks the first time two space telescopes have collaborated to observe a microlensing event — when a distant star brightens due to the gravitational field of at least one foreground cosmic object.
Brown dwarfs
Brown dwarfs are substellar objects that occupy the mass range between the heaviest gas giants and the lightest stars, of approximately 13 to 75–80 Jupiter masses (MJ).
Below this range are the sub-brown dwarfs, sometimes referred to as rogue planets, and above it are the lightest red dwarfs (M9 V). Brown dwarfs may be fully convective, with no layers or chemical differentiation by depth.
Unlike the stars in the main-sequence, brown dwarfs are not massive enough to sustain nuclear fusion of ordinary hydrogen (1H) to helium in their cores. They are, however, thought to fuse deuterium (2H) and to burn lithium (7Li) if their mass is above a debated threshold of 13 MJ and 65 MJ, respectively.
Brown dwarf stars aren’t exactly stars. They’re somewhere between a star and a planet — roughly 80 times the size of Jupiter but not hot enough to generate energy through nuclear fusion.
Brown dwarfs typically orbit a larger star. Interestingly, scientists have found very few brown dwarfs orbiting within three astronomical units of sun-sized stars. An astronomical unit, or AU, is the distance between Earth and the sun.
Researchers were able to ascertain more accurate information about the newly discovered brown dwarf — its size and the distance from its host star — by viewing the microlensing event from more than one angle. The more angles, the better.
