A Clearer Cosmic Picture
A new peak is rising from this snow-capped volcano--an immense, fabricated cone of reinforced concrete that soon will support the world’s largest radio telescope, able to see back nearly to the beginning of time.
It has taken 14 years to conceive, design and build so far, and it will be at least two more years before a 160-foot-diameter antenna dish is installed. Then, not far from where Mexico’s pre-Columbian cultures emerged as leading astronomers, the telescope will start collecting and analyzing radio waves from the most distant galaxies.
The $88-million telescope, located 15,000 feet up on the summit of the extinct Cerro La Negra volcano in Puebla state, is a joint effort of Mexico and the United States.
Both countries stand to benefit from this cross-border cooperation: Mexico will gain critical scientific and technological knowledge; the U.S. team will get bargain-priced, top-notch construc- tion skills as well as one of the most pristine atmospheric settings in the world, free of vapor and dust and ideal for capturing the most distant electromagnetic waves.
The participants include Mexico’s National Institute of Astronomy, Optics and Electronics, the University of Massachusetts and government agencies such as the U.S. Defense Advanced Research Projects Agency.
After six years of planning, construction started in 2000. The original target date for completion was 2002, but several obstacles have pushed back the date by two years.
“The reason for our delay is mainly the enormous engineering challenges that we have faced, which were startling and encouraging at the same time,” said Emmanuel Mendez, director of the project. For one, he noted, the uneven soil forced scientists to drive special pillars 60 feet down into the earth to create a sufficiently strong foundation for the huge superstructure.
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Analyzing Aspects of Early Galaxies
The 46-foot-high concrete cone now visible on the mountain peak is the “basement” that will support a 2,000-ton steel structure on which the antenna dish will be assembled. The antenna will be able to move on two axes, one parallel and one perpendicular to the ground.
The telescope will help scientists analyze three main aspects of early galaxies and solar systems: the molecular composition of dust and gas clouds out of which galaxies are born; the dynamics in which dust and clouds build stars, solar systems and galaxies; and how galaxies evolve.
The instrument will collect electromagnetic emissions with wavelengths between 1 and 4 millimeters.
Those wavelengths are important because they, in effect, pass through the clouds of dust and gases that block radiation in the visible part of the spectrum.
In very distant and early galaxies, “a high amount of star formation is obscured because of dust,” said David Hughes, a cosmologist at the National Institute of Astrophysics and Optics in Puebla, Mexico.
“Optical observation can only suggest it, because you do not see the optical light coming out from young hot stars,” he added. “In the millimeter telescopes, what you see is optical radiation absorbed by dust and re-emitted at millimeter wavelengths.”
No other millimeter telescope in the world will enable observers to reach such distant sites with such resolution. There are two other major millimeter telescopes: the James Clerk Maxwell Submillimeter Telescope in Hawaii, which has a 33-foot dish, and the 100-foot IRAM in Spain’s Sierra Nevada region. With its 160-foot dish, the Puebla telescope should out-see both of them.
The existing millimeter arrays “are sensitive enough to detect” very distant galaxies, “but their resolution is not good enough to actually pick up individual ones,” said Richard Hughes, astronomer at the University of Manchester in Britain. “To distinguish any more, you have to have a bigger telescope that has more resolution so you can actually see the individual objects.”
The galaxies the new telescope is designed to see are so far away that the electromagnetic radiation reaching us has been traveling almost from the beginning of the universe.
“We will be looking at the universe at the earliest stage that it is possible to observe, seeing it as if it were a baby,” said Judy Young, an astronomer at the University of Massachusetts.
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Learning More About Our Solar System
With its ability to observe distant processes of star formation, the giant radio telescope will also be useful for studying the history of our galaxy and solar system.
“To understand how many stars with planets there are, and the chance of finding other solar systems, we have to follow the whole picture from gas and dust into planets,” said Paul Goldsmith, an astronomer at Cornell University who has been part of the project since 1988.
Achieving the extra resolution that will make such observations possible is not just a matter of the Puebla telescope’s greater size, but also its advanced technology. For example, each of the 180 carbon-fiber reflecting panels that will form the telescope’s dish will be electronically operated to form a perfect parabolic shape.
“Even with its nearly 2,000-square-meter area, the deviation caused by wind will never be more than two-tenths of a millimeter,” or the thickness of a piece of paper, said Alfonso Serrano, a Mexican astronomer and chief scientist for the project. “This is an amazing achievement, even given the low winds atop the hill.”
The machinery and instruments have been built on both sides of the border, injecting new expertise into Mexico’s technological arsenal while allowing U.S. scientists to stretch their budgets.
“Mexican low wages and excellent labor skills have made this project possible. Building this telescope in Europe or the U.S. would have been unaffordable,” said Roberto Tepichi, chief engineer in charge of the carbon-fiber panels.
