The Earth’s “ear”

2015-07-29By Yang Chunxue,Yu Fei,Quan Xiaoshu

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A week after the Kepler space telescope eyed an “older, bigger cousin” of the Earth, scientists turned their focus on a super-sensitive “ear”, hoping to discover more, maybe “cousins” of human beings.

In a valley deep in southwest China’s mountainous Guizhou Province, thousands of white steel pillars and cables enclose a large natural hollow.

Formed 45 million years ago with collapse of a karst cave, the hollow is now home to the world's largest radio telescope, with a dish area as large as 30 football fields. It takes about half an hour to make one circuit of its 1600-meter-circumference.


The world's largest radio telescope

Scientists say that it will become a big sensitive “ear”, listening to subtle sounds from distant universes, decoding cosmic messages.

With an investment of 1.2 billion yuan, China’s largest ever astronautics project was begun in March 2011 and will be completed in September next year.


A bird view of the world's largest radio telescope

Technicians are assembling the telescope's reflector, which is 500 meters in diameter and made up of 4,450 panels. Each panel is an equilateral triangle with a side length of 11 meters. Cables are fixed to the back of each panel so that it can change positions with an accuracy of 1 mm, ensuring the telescope can receive from different angles.

Once completed, the Five-hundred-meter Aperture Spherical radio Telescope, or “FAST”, will overtake Puerto Rico's Arecibo Observatory, which is 305 meters in diameter. It will be 10 times more sensitive than the steerable 100-meter telescope near Bonn, Germany, says Zhang Haiyan, deputy director of the general office of the FAST Project.


The Arecibo Observatory in the municipality of Arecibo, Puerto Rico. “FAST” will overtake it to become the world's largest single-aperture telescope next year. Photo from the Internet 

For hundreds of years, human beings have been using optical telescopes to observe the universe by visible light, a type of electromagnetic radiation. The radio telescope operates in the radio frequency of the electromagnetic spectrum where it can detect and collect a wider range of data on radio sources.


FAST under the sky

The first radio antenna for astronomical use was built in 1932, by Karl Guthe Jansky, an engineer with Bell Telephone Laboratories. However, the radio signals from the cosmos were so weak that the total energy collected by all radio telescopes worldwide over the past 70 years is unable to turn a book page. Bigger radio telescopes are badly needed.

In 1993, a tentative project, the Large Telescope (LT), now known as the Square Kilometre Array (SKA), was proposed by astronomers from 10 countries, including China, at the General Assembly of the International Union of Radio Science. A year later, scientists proposed that FAST be built in Guizhou Province as China’s contribution to realizing the SKA units.

In 1994, site surveying started, including geo-morphological features and the distribution of the karst depressions, climate, engineering environment, social environment, and radio interference.

Engineer Zhu Boqin worked on the site selection more than 20 years ago. He recalls that after more than two hours trudging on the rugged mountain road about 150 kilometers south of provincial capital Guiyang, he was impressed by the sight of a large, round depression embraced by verdant hills.


FAST under construction

It was home to 65 people in 12 families in a closed world called “Green Water Village”. With no electricity, the inhabitants had a clear view of the starlit sky at night.

Zhu says that though the villagers didn’t understand the radio telescope, they were excited when scientists explained that they would use it to search for intelligent beings on other planets.


Green Water Village

Formed from the dissolution of soluble rocks, such as limestone, dolomite, and gypsum, the natural shape of a karst formation is close to a sphere. This saved much effort in digging hollows for the dish, says Li Di, a scientist of National Astronomical Observatories, Chinese Academy of Science.

The three hills around the depression make an equilateral triangle, forming a perfect holder for the dish.

The karst formation is also good for draining rainwater and protecting the reflector, Zhu says. Moreover, the surrounding area has "radio silence" as there are no towns and cities within a radius of 5 km and only one county center within 25 km.

The place was finally chosen as the site of the FAST Project.

Local residents were moved away to towns and enjoy better living standards. Villagers in other depression communities admired their luck, saying they should thank the aliens.


Scientists with local residents

In March 2006, an international review and advisory conference on the science and technology of FAST was held in Beijing. The review panel concluded that the FAST Project was feasible and recommended it advanced to the next phase of detailed design and construction.

Funding was approved by the National Development and Reform Commission of China in July 2007.

“Once completed, the radio telescope will maintain a lead position in the world for 20 to 30 years,” says Li Di. “We welcome scientists from around the world to come.”

Major astronomical discoveries, such as pulsars, quasars, cosmic microwave background (CMB) radiation, and interstellar organic molecules, have been made by radio telescopes Among the 10 Nobel Prizes related to cosmology and space, six were attributed to radio telescopes.


FAST under the sky

“Being the world’s largest filled-aperture telescope located at an extremely radio quiet site, its science impact on astronomy will be extraordinary, and it will certainly revolutionize other areas of the natural sciences,” says Nan Rendong, chief scientist of the FAST Project, and a researcher with the Chinese National Astronomical Observatory, Chinese Academy of Sciences.

FAST will enable astronomers to jumpstart many science goals, Nan adds. For example, they could survey natural hydrogen in distant galaxies, detect faint pulsars, look for the first star shining, or even hear possible signals from other civilizations.

The key science goals of FAST are based on observables between 70MHz and 3 GHz, including the 21 cm HI hyperfine structure line, pulsar emissions and radio continuum.


FAST under the sky

Chen Xuelei, a specialist in dark matter and dark energy research at the National Astronomical Observatories of China, says FAST could do large-scale surveys for HI emissions from galaxies, which would help understand the state of dark energy and the speed of cosmic expansion.

Scientists also expect breakthroughs on pulsars, the highly magnetized, rotating neutron stars that emit a beam of electromagnetic radiation.

So far more than 2,000 pulsars have been detected. “We expect FAST might detect 50 to 80 pulsars in M31, the nearest major galaxy to the Milky Way,” says Li.


The Milky Way above FAST

High sensitivity and larger sky coverage compared with Arecibo make FAST a powerful tool for detecting weak-emission pulsars at long distances, like millisecond pulsars, binary pulsars, double pulsars and extragalactic pulsars, says Nan.

It is estimated that FAST, equipped with multi-beam receivers, could detect some 7,000 pulsars in the Milky Way in less than a year, Nan adds.

There are many unsolved mysteries in pulsars, says Chen. For example, millisecond pulsars’ rotational period measures in the range of about 1 to 10 milliseconds. “Why do they rotate so fast? It deserves more research,” he says.

“Pulsars are like space labs, in which scientists can study gravitational waves, curved space-time around black holes, and the interstellar medium,” Chen adds. “Many scientists believe that pulsar positioning could create a spacecraft navigation system, or be an auxiliary device to GPS instruments.”


FAST under construction

Perhaps the most exciting goal of FAST is the search for other life. Instead of searching for life per se, scientists are looking for the molecules that constitute life.

Scientists have found about 180 kinds of molecules in space, including carbonic oxide, ammonia, and methanol.

Li estimates that in two or three years, scientists could find amino acid, the foundation block of life. Li is positive that one day people will find life on other planets or galaxies.

“Just like eating and sleeping, curiosity about space is a basic instinct of human beings,” says Li. “Chinese scientists have made numerous contributions in mathematics, computer sciences, and particle physics in the past years under impoverished conditions, and now with the most advanced facility supported by the government, we are duty-bound to make a giant step forward.”


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