Researchers have discovered a new object that is now cool as a planet but the evidence revealed that in its diverse history it might have been a hot fiery star.
Entitled ‘WISE J0304-2705’, the object was a member of the recently established ‘Y dwarf’ class, the coolest stellar temperature class yet defined, added to the end of the sequence OBAFGKMLT. Although its temperature was not far off that of our own world, the object was not like the rocky Earth-like planets and instead was a giant ball of gas like Jupiter.
The current temperature of the object was 100-150 degrees Celsius, intermediate between that of the Earth and Venus. But the object showed evidence of a possible ancient origin, implying that a large change in temperature has taken place. In the past this object would have been as hot as a star for many millions of years.
The international discovery team, led by Prof. David Pinfield at the University of Hertfordshire, identified the Y dwarf using the Wide-field Infrared Survey Explorer (WISE) observatory, a NASA space telescope that since its launch in 2009 has imaged the entire sky in mid-infrared. The team also dispersed the light emitted by the Y dwarf into a spectrum, which allowed them to determine its current temperature and better understand its history.
If WISE J0304-2705 was an ancient object then its temperature evolution would have followed the stages shown in the illustration. During the first 20 million years or so of its life it would have had a temperature of at least 2800 degrees C. At a billion years of age it would have cooled to about 1000 degrees C, cool enough for methane gas and water vapour to dominate its appearance. And since then it has continued to cool to its current temperature of 100 to 150 degrees C.
The study is published in the journal the Royal Astronomical Society.