ESO VLT
ESO's Very Large Telescope used to look for non-existent brown dwarfESO

A brown dwarf that is supposed to be orbiting a pair of stars 163 light years from Earth is not there, scientists have said, throwing up an interstellar mystery for astronomers.

The stellar pair, called V471 Tauri, is a member of the Hyades star cluster in the constellation of Taurus.

The pair are extremely close to one another, orbiting each other once every 12 hours. Twice every hour, one passes in front of the other, leading to changes in the brightness of the pair observed from Earth.

Using ESO's New Technology Telescope, astronomers from the Universidad Valparaiso in Chile measured the brightness changes extremely precisely and discovered the eclipse timings were not regular.

These irregularities could, however, be explained by assuming there was a brown dwarf orbiting the two stars, the gravitational pull from which was disturbing their orbits. They also said another smaller object could be present nearby.

But when they came to locate the brown dwarf with the Very Large Telescope's Sphere instrument, the astronomers saw nothing, raising the question that if there is no orbiting object, what is causing the irregular eclipse timings?

Researchers say that while there are number of possibilities, it could be the result of magnetic field variations in the larger of the two stars.

Lead astronomer Adam Hardy said: "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.

"This is an excellent way to start the observational life of this amazing instrument."