Chuck Bednar for redOrbit.com – @BednarChuck
Not much escapes the sight of the European Southern Observatory’s Very Large Telescope in Chile, but astronomers using the powerful four-telescope array have been unable to pinpoint the location of a brown dwarf star believed to be orbiting a nearby binary star system.
According to CNET, ESO officials revealed on Wednesday that they have been unable to find the brown dwarf suspected to be in orbit around V471 Tauri, located about 163 light-years from Earth. It is a member of the Hyades star cluster in the constellation Taurus, is an estimated 600 million years old, and contains two very close stars that orbit each other every 12 hours.
[Related story: What are brown dwarf stars?]
Rotating orbits
Twice per orbit, one star passes in front of the other, which causes regular changes in how bright the pair of stars are when they are observed from Earth. One of the stars is a white dwarf and the other is a normal star similar to our sun, and as they eclipse one another, astronomers are able to monitor the changing light signals from the binary system, the website added.
Using the Ultracam system on ESO’s New Technology Telescope, a camera capable of taking up to 500 pictures per second and in three different colors at the same time, Adam Hardy of Chile’s Universidad Valparaíso and his colleagues precisely measured these changes.
[Related story: Asteroid anatomy studied with New Technology Telescope]
They found that the timings of the eclipses were not regular, but this phenomenon could be explained by the presence of a brown dwarf orbiting both stars that disrupted their orbits with its gravitational pull. Until recently, however, it was impossible to actually capture an image of a faint brown dwarf located so close to much brighter stars, the ESO explained in a statement.
Sphere changed the game
The recently-installed Sphere instrument on the VLT gave the astronomers the ability to look for the brown dwarf for the first time. Sphere, a “powerful planet finder” that the ESO explained was designed “to detect and study new giant exoplanets orbiting nearby stars” by essentially trying to “capture images of the exoplanets directly, as though it were taking their photograph.”
The instrument was powerful enough to give Hardy’s team their first look at the brown dwarf, but there was one problem – it wasn’t there. They pointed Sphere at the binary system expecting to find the companion, but the brown dwarf they expected to see was nowhere to be found.
[Related story: First light for Sphere exoplanet hunter]
“The Sphere images are so accurate that they would have been able to reveal a companion such as a brown dwarf that is 70,000 times fainter than the central star, and only 0.26 arcseconds away from it. The expected brown dwarf companion in this case was predicted to be much brighter,” the ESO said.
Other theories
So if the object influencing the obit of those stars isn’t a brown dwarf, what is it? One possible theory is that the effects are being caused by magnetic field variations in the larger of the binary stars, similar to smaller changes that have been observed in the Sun. CNET explains that this is known as the Applegate mechanism, and it causes the actual shape of the star to change.
The astronomers have published their findings in the Astrophysical Journal Letters, and along with Hardy and colleagues from Universidad Valparaíso and the ESO, researchers from the University of Warwick, the University of Sheffield and Universidad Diego Portales were listed as co-authors on the paper.
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