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.