Two of the oldest brown dwarfs in the Galaxy have been discovered by researchers from the University of Hertfordshire.
According to a press statement, researchers from the University revealed that the two ancient objects were moving at a speed of approximately 200 kilometers per second, which is much faster than the speed of other normal stars and brown dwarfs. Researchers believe that both these stars may have formed more than 10 billion years ago, when the galaxy was still very young. They also speculate that these brown dwarfs may have been part of a vast and previously unseen population of cosmic objects.
Brown dwarfs are space objects that have much less mass than normal stars. Generally they have a mass less than 7percent that of the Sun. They also don't generate internal heat through nuclear fusion like stars. Owing to this, brown dwarfs are very cold and slowly fade away with time. The newly discovered dwarfs have temperatures of 250-600 degrees Celsius, much cooler than stars.
Dr David Pinfield who led the discovery, first identified the two objects with the help of a NASA observatory that scanned the mid-infrared sky from orbit in 2010 and 2011 named Wide-field Infrared Survey Explorer (WISE). Accordingly, both the newly discovered cosmic objects have been named WISE 0013+0634 and WISE 0833+0052. They were found in the Pisces and Hydra constellations, respectively. It is not easy to identify a brown dwarf in the infrared sky, which is filled with faint red sources like reddened stars, nebulous gas and dust. Therefore, Pinfield and his team were forced to develop a new method by which WISE scanned the skies, making it possible to detect brown dwarfs that were fainter than what previous searchers had revealed.
After studying the light emitted by these objects, researchers found that their light was different compared to typical slower moving brown stars. The spectral of their light also provided insight into their ancient atmospheres. Researchers noted that their atmosphere comprised mostly of hydrogen rather than other heavier elements commonly found in abundance in normal stars.
Stars closer to the Sun generally have three overlapping populations - the thin disk, the thick disk and the halo. The thin disk is younger than the thick disk and stars in the latter population move at a higher velocity.
90 percent of stars fall into the thin disk population with stars of the thick disk or halo populations being very rare. This is one explanation why stars belonging to these two populations are only just being discovered.
"These two brown dwarfs may be the tip of an iceberg and are an intriguing piece of astronomical archaeology", said Pinfield. "We have only been able to find these objects by searching for the faintest and coolest things possible with WISE. And by finding more of them we will gain insight into the earliest epoch of the history of the Galaxy."
