Weekly Science Update

Wednesday, July 11, 2007
Cosmic Discoveries Near and Far
Astronomy, unlike many other scientific disciplines, has no laboratories where its experiments can unravel the secrets of nature. Instead, it relies on meticulous and clever observations of remote phenomena. Knowing what to look for in the wide heavens has, therefore, always been a valuable skill. "Sky surveys" are systematic studies, undertaken at specific wavelengths, of everything detectable in a particular part of the sky. Their inclusive nature means that unexpected objects, or even previously unknown kinds of phenomena, will be observed, and -- if they are spotted as being unusual -- can subsequently be studied.

The Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope is the most sensitive infrared system of its type now existing; it was built by a team led by SAO astronomers. As part of its research programs, IRAC undertook a sky survey in a region of sky about twenty times bigger than the full moon in angular diameter, in the direction of the constellation of Bootes. A paper in the July 1 issue of the Astrophysical Journal announces two of its most dramatic results -- the simultaneous discoveries of a quasar at the farthest reaches of the universe and a very small star only fifteen times bigger than Jupiter and a mere 100 light-years away.

SAO astronomers Lori Allen and Howard Smith, together with a team of seventeen other scientists, combined the IRAC survey results with data from the Chandra X-ray observatory and five other surveys to spot (among nearly 300,000 objects!) two that were distinguished by their very red colors. Follow-up studies from ground-based telescopes determined that one of them was a quasar -- a luminous galaxy powered, astronomers think, by a central, supermassive black hole -- and so far away that the universe was only about 890 million years old when it was bright, or about 7% of its current age. This object is one of the ten most distant quasars known, the only one that is also a bright source at radio wavelengths, and that is most likely the result of two or more colliding galaxies. It is red because of a combination of cosmic motions and intergalactic dust.

The other object turns out to be a relatively close neighbor of the Earth's, only about 100 light-years away. It is a small star -- a "brown dwarf" -- whose mass is about the same as fifteen Jupiters, barely enough to sustain nuclear reactions and tantalizingly close to making the body a planet instead of a star. It is red because it is so cool, and because molecules like methane and/or water in its photosphere preferentially absorb the bluer light. This is the first known example of such a cool brown dwarf that is not orbiting around another star (the usual method of discovering these objects). These two dramatic results highlight the value of unbiased searches of the skies.

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