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Closest new stars found for a century

Paul Sutherland, News Editor
31 March 2013, 0:00 UTC

Sen— Using powerful telescopes, astronomers can today see so far that galaxies have been observed as they were just a few million years after the Big Bang. But there are still big surprises to be found right on our cosmic doorstep.

Amazing as it seems, a space telescope has recently discovered a pair of stars that are the third closest stellar system to us in the Universe at a distance of only 6.5 light-years.

They are the first nearby stars found for nearly 100 years because the last such find was made in 1916.

The stars were previously missed because they are of a very dim type called brown dwarfs - stars with too little mass ever to become hot enough to ignite. They are therefore cool and more like Jupiter, and were spotted thanks to a heat-seeking NASA space telescope called the Wide-field Infrared Survey Explorer (WISE) which launched in 2009.

This telescope was sensitive to pick up the faint glow of the stars which have now been given the telephone-number label of WISE J104915.57-531906. Kevin Luhman, associate professor of astronomy and astrophysics at Penn State University in the USA and a researcher in Penn State’s Center for Exoplanets and Habitable Worlds, made the discovery.

At first they appeared to be one single object but ground observations from the Gemini South telescope in Chile showed them in sharper detail, revealing that this was a binary star system.

Images of brown dwarf system

A WISE image of the newly found stellar system with Gemini's photo inset to reveal that it is a pair of stars. Credit: NASA/JPL/Gemini Observatory/AURA/NSF

The closest stars to the Earth are the Alpha Centauri family of three stars which lies a little over 4 light-years away. Its brightest star, Alpha itself, was found to be our neighbour in 1839 and lies 4.4 light-years. But its fainter companion Proxima Centauri, seen to be a neighbour in 1912, is even closer at 4.2 light-years.

Slightly further away is Barnard’s star which was found 6.0 light-years away in 1916. That revealed itself because of its rapid motion across the sky. Most stars appear relatively fixed in the heavens but its movement is obvious in photos taken just a few months or years apart.

It was its rapid motion that also gave away the new find, WISE J104915.57-531906. Luhman found it by studying images taken by WISE over a 13-month period ending in 2011. Shots of the same area of sky revealed the runaway pair.

Luhman said: “In these time-lapse images, I was able to tell that this system was moving very quickly across the sky - which was a big clue that it was probably very close to our Solar System.”

The discovery prompted Luhman to look for earlier images showing the stars. He found that it had been recorded in pictures taken between 1978 and 1999 in the Digitized Sky Survey, the Two Micron All-Sky Survey, and the Deep Near Infrared Survey of the Southern Sky.

WISE satellite

An artist's concept of the WISE space telescope operating in Earth orbit. Credit: NASA/JPL-Caltech

He said: “Based on how this star system was moving in the images from the WISE survey, I was able to extrapolate back in time to predict where it should have been located in the older surveys and, sure enough, it was there.”

By comparing images taken in different surveys, Luhman was also able to calculate the star system’s distance. He then obtained a spectrum using the Gemini South telescope which confirmed them to be cool brown dwarfs.

Luhman added: “The distance to this brown dwarf pair is 6.5 light years - so close that Earth’s television transmissions from 2006 are now arriving there. It will be an excellent hunting ground for planets because it is very close to Earth, which makes it a lot easier to see any planets orbiting either of the brown dwarfs.”

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