The Universe Tonight

Aug 1, 2009 6:00pm
The Submillimeter Array, Anil Dosaj

The Submillimeter Array

 By Anil Dosaj

The Submillimeter Array

 The Submillimeter Array (SMA) explores the universe by detecting light of colors that are not visible to the human eye. It receives millimeter and submillimeter radiation, so named because it's wavelength ranges from 0.3 to 1.7 millimeter, or 0.01 to 0.07 inches.

The main source of millimeter and submillimeter radiation is cold interstellar material. It consists of gas, dust and small rock-like bodies. This material is also the substance out of which stars and planets are formed. Detecting submillimeter emission therefore plays a vital role for studying the birth and death of stars. When stars are born out of dense interstellar clouds, their first visible light is trapped within them. The SMA can see into those clouds and acquire detailed images of the submillimeter light and thereby witness the birth of a star where optical telescopes or human eyes can just see darkness.

The resolution of any telescope is determined by the diameter of its mirror divided by the wavelength (color) of the light being observed. As we move to longer and longer wavelengths this relationship causes a telescopes' resolution to worsen. To see the same resolution at longer wavelengths astronomers have to build larger telescopes. First used in radio frequencies, the SMA employs a technique called interferometry whereby light from a number of smaller telescopes is combined to "synthesize" one large telescope. The SMA is the world's first imaging interferometric telescope at the submillimeter wavelengths. It consists of 8 movable antennas that can be positioned along the sides of a Reuleaux triangle to provide optimal imaging quality. Each antenna is composed of a smooth parabolic reflector 6 meters (19 and 2/3 feet) in diameter. The signals from the antennas are amplified and combined electronically to give the resolution equivalent to an antenna of 0.5 km (0.3 miles) across.

The SMA is located at the foot of Pu'u Poli'ahu at 4080 m above sea level (13,386 feet) at the summit of Mauna Kea. The submillimeter emission from astronomical objects is partially absorbed by water 
vapor in the Earth's atmosphere. At sea level, little submillimeter radiation reaches the Earth's surface, and submillimeter astronomical observations are impossible. By building the SMA on a high and dry 
site, the radiation can be detected and measured through this atmosphere window. 

Speaker Biography

I received my BA in Astronomy at the the University of Texas at Austin (1993), my MS in Astronomy at San Diego State University (1997).  I went to work for the Chandra Xray Observatory from 1998-2002 and 2004-2007 as a mission planner (science scheduling of the telescope) and the Director's office (user support stuff).  I was briefly back in grad school from 2002-2004 at the University of Wisconsin, Madison, but did not complete a degree there.  I then Worked for Gemini Observatory from May 2007-October 2008 as a data analyst.  I have been a telescope operator for the SMA since October of 2008.


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