The two oldest brown dwarfs of the Universe

Two brown dwarfs discovered so far have an unknown origin and they are estimated to have more than ten billion years. They could be part of a vast and as yet unknown, stellar population. A researcher of INAF Astronomical Observatory of Turin had participated among the authors of the study.



They are small, fast and very, very old. The two stars just identified by the team of astronomers led by David Pinfield of the University of Hertfordshire could be two of the oldest brown dwarfs in our galaxy. Visible in the constellations of Pisces and Hydra, new discoveries are moving at about 100-200 kilometers per second, much faster than normal stars or other known brown dwarfs. And probably they were formed more than ten billion years ago, when the galaxy was still very young.

But the most fascinating thing is that the two dwarf stars could be part of a large population of celestial objects never seen before: in this case it would be only the “tip of the iceberg”, in the words of David Pinfield. The scientist added: “The two brown dwarfs are an intriguing piece of archeology astronomy. We were able to find only the coolest looking and soft possible objects detected by WISE. ”

WISE stands for Wide-field Infrared Survey Explorer, a NASA observatory that has been in orbit from 2010 to 2011, giving astronomers a valuable mine of information. For this reason, the two new discoveries have taken its name respectively WISE 0013 +0634 and WISE 0833 +0052, and their presence has been confirmed by several ground-based telescopes ( Magellan, Gemini , UKIRT and VISTA ).

The research was published in the Monthly Notices of the Royal Astronomical Society and involved astronomers in various parts of the world. Among the signatures also appears Catia Cardoso, a researcher at INAF Turin Astronomical Observatory. “We used some of the data coming from the Italian TNG telescope which served for the initial classification of the two stars,” said Cardoso. “The stars were moving very quickly across the sky, and so we knew they belong to different populations from those that we normally watch.”



Locating the two brown dwarfs firm was in fact far from obvious: the infrared sky, in which WISE moved, is full of nebulous gas, dust and other very distant galaxies of the Milky Way. For this reason, Pinfield team has developed a new method, which takes advantage of the way in which WISE scans several times the same portion of the sky. This has allowed astronomers to detect dwarf stars, cooler and brighter than the light of the other celestial objects detected. By analyzing the infrared spectra emitted from brown dwarfs it was possible to determine the age of their atmosphere, composed almost entirely of hydrogen and other heavier elements, present in younger stars.

The great age of the two brown dwarfs confirmed once more that the weather does not have a unique value in the Universe: “Apparently, the oldest inhabitants of the galaxy move faster than younger ones,” says Pinfield .

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