A brown dwarf was predicted to be within a stellar system, but even the Very Large Telescope (VLT) in Chile cannot spot the missing body.
The Spectro-Polarimetric High-contrast Exoplanet Research (Sphere) instrument at the observatory was used to examine a binary star system, known as V471 Tauri, located roughly 163 light years from our local star. They make up a common-envelope binary, in which an aging red giant star loses gas to its white dwarf companion, surrounding both stars in gaseous material. Over time, the gas escapes to space. During this process, the pair of stars draws closer to one another, through the force of gravity.
As the two stars orbit around their common center of mass, one of the bodies passes along the line of sight seen by astronomers on Earth. When this happens, light from the other body is reduced, allowing astronomers to calculate the orbital period of the pair. The V471 Tauri system exhibits two of these passes each 12 hours. However, examination of data from the Ultracam system on the New Technology Telescope revealed this period is irregular, suggesting the presence of a cool, dark, unseen companion.
The binary pair is seen in the Hyades star cluster, within the constellation of Taurus. The system is believed to be around 600 million years old, much younger than our own solar system.
Brown dwarfs are larger than planets, but smaller than stars. They do not possess enough matter, and gravity, to sustain nuclear fusion in their cores, and ignite as stars. These bodies are exceptionally dim, and difficult to image. The Sphere instrument is designed to record the presence of dim astronomical bodies 70,000 times dimmer than their stellar companions, and should have been able to record a brown dwarf with the predicted qualities. However, images taken of the spot where the brown dwarf should have been revealed no evidence of a body in that position.
As the predicted brown dwarf did not appear in images, researchers on the project believe theories on the orbital patterns of these stars could be wrong. Astronomers are uncertain what could be responsible for the irregular orbit of V471 Tauri, although it is possible the magnetic field of the larger companion could cause the effect.
"A study such as this has been necessary for many years, but has only become possible with the advent of powerful new instruments such as SPHERE. This is how science works: observations with new technology can either confirm, or as in this case disprove, earlier ideas," Adam Hardy of the Universidad Valparaíso said.
Examination of the results of the study of V471 Tau was detailed in the Astrophysical Journal Letters.
