NEWS ARCHIVEPlanet-like object may have spent its youth as hot as a star
Astronomers have discovered an extremely cool object that could have a particularly diverse history - although it is now as cool as a planet, it may have spent much of its youth as hot as a star. The team publish their results in the journal Monthly Notices of the Royal Astronomical Society. The current temperature of the object is 100-150 degrees Celsius, intermediate between that of the Earth and Venus. But the object shows 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 light (rather redder than the reddest light we can see with our eyes). 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. Only 20 other Y dwarfs have been discovered to date, and amongst these WISE J0304-2705 is defined as 'peculiar' due to unusual features in its emitted light spectrum. "Our measurements suggest that this Y dwarf may have a composition and/or age characteristic of one of the Galaxy's older members" explains Prof Pinfield. "This would mean its temperature evolution could have been rather extreme – despite starting out at thousands of degrees this exotic object is now barely hot enough to boil a cup of tea." The reason that WISE J0304-2705 underwent such extensive evolutionary cooling is because it is "sub-stellar" - its interior never became hot enough for hydrogen fusion, the process that has kept the Sun hot for billions of years. And without an energy source maintaining a stable temperature, cooling and fading was inevitable. If WISE J0304-2705 is 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 °C, the same as red dwarf stars like Proxima Centauri (the nearest star to the Sun). After 100 million years it would have cooled to about 1500 °C, with silicate clouds condensing out in its atmosphere. At a billion years of age it would have cooled to about 1000 °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 °C. WISE J0304-2705 is as massive as 20 to 30 Jupiters combined, so somewhere between the least massive stars and typical planets. But in terms of temperature it may have actually "taken the journey" from star-like to planet-like conditions. Having identified WISE 0304-2705, Prof Pinfield's team made crucial ground-based observations with some of the world's largest telescopes - the 8m Gemini South Telescope, the 6.5m Magellan Telescope and the European Southern Observatory's 3.6m New Technology Telescope, all located in the Chilean Andes. Team member Dr Mariusz Gromadzki said "The ground based measurements were very challenging, even with the largest telescopes. It was exciting when the results showed just how cool this object was, and that it was unusual." "The discovery of WISE J0304-2705, with its peculiar light spectrum, poses ongoing challenges for the most powerful modern telescopes that are being used for its detailed study" remarked Prof. Maria Teresa Ruiz, team member from the Universidad de Chile. WISE J0304-2705 is located in the constellation of Fornax (The Furnace) in the southern hemisphere of the sky, belying its cool temperature, and is between 33 and 55 light years away. There is currently no lower limit for Y dwarf temperatures, and there could be many even cooler and more diverse objects un-detected in the solar neighbourhood. WISE went into hibernation in February 2011 after carrying out its main survey mission. However, by popular demand it was revived in December 2013, and is continuing to observe as part of a 3 year mission extension. "WISE gives us wonderful sensitivity to the coolest objects" said Prof. Pinfield, "and with 3 more years of observations we will be able to search the sky for more Y dwarfs, and more diverse Y dwarfs."
Science contacts Prof David Pinfield Dr Mariusz Gromadzki Dr Sandy Leggett Prof Maria Teresa Ruiz Dr Radostin Kurtev
Media contacts Robert Massey Natasha Metzler Peter Michaud
Image and caption Download an image to illustrate this work Caption: A four-stage sequence (left to right) showing the possible extreme temperature evolution for WISE J0304-2705. When young the object was as hot as a star, shining with a temperature of at least 2800 degrees C for about 20 million years. After 100 million years or so it had cooled to 1500 degrees C, and by a billion years its temperature was around 1000 degrees C. The final stage is billions of years later, when WISE J0304-2705 had cooled to its current planetary temperature of 100-150 degrees C. Credit: John Pinfield, 2014
Further information The results are published in the paper D. J. Pinfield, M. Gromadzki, S. K. Leggett, J. Gomes, N. Lodieu, R. Kurtev, A. C. Day-Jones, M. T. Ruiz, N. J. Cook, C. V. Morley, M. S. Marley, F. Marocco, R. L. Smart, H. R. A. Jones, P. W. Lucas, Y. Beletsky, V. D. Ivanov, B. Burningham, J. S. Jenkins, C.Cardoso, J. Frith, J. R. A. Clarke, M. C. Gálvez-Ortiz and Z. Zhang, "Discovery of a new Y dwarf: WISE J030449.03-270508.3", Monthly Notices of the Royal Astronomical Society, in press, published by Oxford University Press. A pre-publication version of the paper is available on the arXiv. Useful links: University of Hertfordshire Centre for Astrophysics Research The Magellan Telescope
Notes for editors The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organises scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. Follow the RAS on Twitter via @royalastrosoc The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai'i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space. The Gemini Observatory provides the astronomical communities in six partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the U.S. National Science Foundation (NSF); the Canadian National Research Council (NRC); the Brazilian Ministério da Ciência, Tecnologia e Inovação (MCTI); the Australian Research Council (ARC); the Argentinean Ministerio de Ciencia, Tecnología e Innovación Productiva; and the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT). Gemini is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership. |
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